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{
"id": 5772874,
"topic": "gcn.circulars",
"uuid": "845f2899-64d9-4da6-9460-e8f0dfc1981b",
"title": "EP250821a: Gemini GMOS Redshift Confirmation",
"submitter": "Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"authors": "Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41549"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250821a",
"subject": "EP250821a: Gemini GMOS Redshift Confirmation",
"createdOn": 1756223383103,
"submitter": "Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"circularId": 41549,
"submittedHow": "web"
},
"message_text": "\nBrendan O'Connor (CMU), Xander Hall (CMU), Antonella Palmese (CMU) report on behalf of a larger collaboration:\n\nWe observed the location of EP250821a (Hu et al. GCN 41459; Liang et al., GCN 41467) with the Gemini GMOS-S spectrograph starting on 2025-08-26 at 01:53:43 UT. Our spectra cover wavelengths 575 to 1060 nm and consist of 4x1200 s exposures using the R400 grating. In a preliminary reduction, at the location of the optical counterpart (Dichiara et al., GCN 41469; Li et al. GCN 41470; Yao et al. GCN 41485), we clearly detect a bright trace. We detect multiple emission lines from the underlying host galaxy, including [OII], [OIII], Hbeta, [NII], and Halpha, at a consistent redshift of z=0.577. This confirms the previous spectroscopic redshift obtained by the VLT (An et al., GCN 41490).\n\nWe thank the staff of the Gemini Observatory, in particular Karleyne Silva, Cinthya Rodriguez, Aleksandar Cikota, Emanuele Farina, for assistance with scheduling and obtaining these observations. ",
"published": "2025-08-26T15:49:52.297421Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-26T15:49:52.297438Z",
"modified": "2025-08-26T15:49:52.314643Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5787694,
"topic": "gcn.circulars",
"uuid": "72915ca3-8fc9-4367-ab98-1d4cac21ea87",
"title": "EP250821a: iTelescope T-59 possible detection of the optical counterpart",
"submitter": "Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>",
"authors": "Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42089"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42089....1B",
"eventId": "EP250821a",
"subject": "EP250821a: iTelescope T-59 possible detection of the optical counterpart",
"createdOn": 1759496377589,
"submitter": "Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>",
"circularId": 42089,
"submittedHow": "web"
},
"message_text": "H. Ban, T. Katou, Y. Nagata, K. Hotta, Y. Kawakubo, M. Serino, T. Sakamoto (AGU)\n\nWe observed the field of EP250821a detected by the Einstein Probe (EP) \n(Hu et al., GCN Circ. 41459) with the iTelescope.Net\n(http://www.itelescope.net) T59 (Planewave 20\" CDK) telescope located at \nthe Siding Spring Observatory, Australia. We took nine images of 120-second \nexposures in the Red filter starting from August 21 at 10:25:34 (UT), \nabout 3 hours after the trigger, and stopped at 12:48:14 (UT). Please note \nthat there were no observations between 10:33 and 11:30, and \nbetween 11:39 and 12:41 due to our scheduling error.\n\nWe have a weak detection of the optical counterpart \n(Dichiara et al., GCN Circ. 41469; Li et al., GCN Circ. 41470; \nYao et al., GCN Circ. 41485) in the stacked image of the first \nthree exposures from 10:25:34 to 10:32:47 UT. The estimated magnitude \nis ~18.5. No optical counterpart was detected in the following six images \ncollected between 11:30:00 and 12:48:14 (UT). The 5-sigma upper limit \nof the stacked image of the last six images is 17.5 mag.",
"published": "2025-10-13T08:09:07.875316Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-10-13T08:09:07.875321Z",
"modified": "2025-10-13T08:09:07.879392Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5784368,
"topic": "gcn.circulars",
"uuid": "6ce36a25-3985-42ab-be7c-992d5e71ecce",
"title": "EP250821a: iTelescope T-59 possible detection of the optical counterpart",
"submitter": "Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>",
"authors": "Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42089"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250821a",
"subject": "EP250821a: iTelescope T-59 possible detection of the optical counterpart",
"createdOn": 1759496377589,
"submitter": "Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>",
"circularId": 42089,
"submittedHow": "web"
},
"message_text": "H. Ban, T. Katou, Y. Nagata, K. Hotta, Y. Kawakubo, M. Serino, T. Sakamoto (AGU)\n\nWe observed the field of EP250821a detected by the Einstein Probe (EP) \n(Hu et al., GCN Circ. 41459) with the iTelescope.Net\n(http://www.itelescope.net) T59 (Planewave 20\" CDK) telescope located at \nthe Siding Spring Observatory, Australia. We took nine images of 120-second \nexposures in the Red filter starting from August 21 at 10:25:34 (UT), \nabout 3 hours after the trigger, and stopped at 12:48:14 (UT). Please note \nthat there were no observations between 10:33 and 11:30, and \nbetween 11:39 and 12:41 due to our scheduling error.\n\nWe have a weak detection of the optical counterpart \n(Dichiara et al., GCN Circ. 41469; Li et al., GCN Circ. 41470; \nYao et al., GCN Circ. 41485) in the stacked image of the first \nthree exposures from 10:25:34 to 10:32:47 UT. The estimated magnitude \nis ~18.5. No optical counterpart was detected in the following six images \ncollected between 11:30:00 and 12:48:14 (UT). The 5-sigma upper limit \nof the stacked image of the last six images is 17.5 mag.",
"published": "2025-10-03T12:59:45.915196Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-10-03T12:59:45.915217Z",
"modified": "2025-10-03T12:59:45.939467Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776756,
"topic": "gcn.circulars",
"uuid": "ac710f38-f0cc-475b-889a-778e91f1b6db",
"title": "EP250821a: MeerKAT radio counterpart",
"submitter": "Francesco Carotenuto at INAF/OAR <francesco.carotenuto@inaf.it>",
"authors": "Francesco Carotenuto at INAF/OAR <francesco.carotenuto@inaf.it>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41530"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41530....1C",
"eventId": "EP250821a",
"subject": "EP250821a: MeerKAT radio counterpart",
"createdOn": 1756054244310,
"submitter": "Francesco Carotenuto at INAF/OAR <francesco.carotenuto@inaf.it>",
"circularId": 41530,
"submittedHow": "web"
},
"message_text": "Authors: F. Carotenuto (INAF-OAR), J. Bright (Oxford), P. G. Jonker (Radboud), on behalf of a larger collaboration\n\nWe observed the field of EP250821a detected by the Einstein Probe (GCN 41459, 41470, 41490) with the MeerKAT radio telescope from 2025-08-23 21:44 UTC to 2025-08-23 22:31 UTC (with a total time on source of 44 minutes) using the S-band receivers at a central frequency of 3.06 GHz. Analysing the SARAO Science Data Processor output continuum image, we detect a source at the position of EP250821a with a flux density of around 40 uJy/beam, with a typical image noise of around 6 uJy/beam. Pending verification on the host galaxy emission, we tentatively ascribe it to EP250821a.\n\nFurther observations are planned.\n\nWe thank the SARAO staff for rapidly scheduling these observations. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation. This work has made use of the \"MPIfR S-band receiver system\" designed, constructed and maintained by funding of the MPI für Radioastronomie and the Max-Planck-Society.",
"published": "2025-09-08T08:08:57.074666Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:57.074684Z",
"modified": "2025-09-08T08:08:57.078820Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5772382,
"topic": "gcn.circulars",
"uuid": "200ce27a-7c6a-47a3-97c8-f8030e63244f",
"title": "EP250821a: MeerKAT radio counterpart",
"submitter": "Francesco Carotenuto at INAF/OAR <francesco.carotenuto@inaf.it>",
"authors": "Francesco Carotenuto at INAF/OAR <francesco.carotenuto@inaf.it>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41530"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250821a",
"subject": "EP250821a: MeerKAT radio counterpart",
"createdOn": 1756054244310,
"submitter": "Francesco Carotenuto at INAF/OAR <francesco.carotenuto@inaf.it>",
"circularId": 41530,
"submittedHow": "web"
},
"message_text": "Authors: F. Carotenuto (INAF-OAR), J. Bright (Oxford), P. G. Jonker (Radboud), on behalf of a larger collaboration\n\nWe observed the field of EP250821a detected by the Einstein Probe (GCN 41459, 41470, 41490) with the MeerKAT radio telescope from 2025-08-23 21:44 UTC to 2025-08-23 22:31 UTC (with a total time on source of 44 minutes) using the S-band receivers at a central frequency of 3.06 GHz. Analysing the SARAO Science Data Processor output continuum image, we detect a source at the position of EP250821a with a flux density of around 40 uJy/beam, with a typical image noise of around 6 uJy/beam. Pending verification on the host galaxy emission, we tentatively ascribe it to EP250821a.\n\nFurther observations are planned.\n\nWe thank the SARAO staff for rapidly scheduling these observations. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation. This work has made use of the \"MPIfR S-band receiver system\" designed, constructed and maintained by funding of the MPI für Radioastronomie and the Max-Planck-Society.",
"published": "2025-08-24T16:50:45.502881Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-24T16:50:45.502899Z",
"modified": "2025-08-24T16:50:45.521448Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776667,
"topic": "gcn.circulars",
"uuid": "81f0ddf9-23d4-4094-9eb3-67c2e5dfbb00",
"title": "EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations",
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"authors": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41467"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41467....1L",
"eventId": "EP250821a",
"subject": "EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations",
"createdOn": 1755793626159,
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"circularId": 41467,
"submittedHow": "web"
},
"message_text": "Y. F. Liang, D. F. Hu (PMO, CAS), C. C. Jin (NAO, CAS) report on behalf of the Einstein Probe team:\n\nThe X-ray transient EP250821a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 41459). We report on the further results of WXT and FXT observations. The analysis of the WXT data shows that the event started at T0=2025-08-21T07:17:04 (UTC) and lasted for at least 80 s. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 7.33 x 10^20 cm^-2 and a photon index of 1.2 (-/+0.5). The derived average unabsorbed 0.5-4 keV flux is 1.3(-/+0.4) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.\n\nThe Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 320 s after T0. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 289.8862, DEC = -43.3808 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), within the WXT error circle. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.25 x 10^21 cm^-2 and a photon index around 3.5. The derived average unabsorbed 0.5-10 keV flux is about 2.6 x 10^(-10) erg/s/cm^2 during the time interval from 0 to 1000 seconds after the start of the observation.The results from FXT may have been affected by pile-up effect, particularly in the brightest time interval. Therefore, the values reported here should be considered preliminary and are intended to provide a rough estimate of the source intensity.\n\nLaunched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). ",
"published": "2025-09-08T08:08:47.865953Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:47.865971Z",
"modified": "2025-09-08T08:08:47.870131Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5771602,
"topic": "gcn.circulars",
"uuid": "a5d493a7-3eda-4556-8483-42bc9233bc98",
"title": "EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations",
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"authors": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41467"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250821a",
"subject": "EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations",
"createdOn": 1755793626159,
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"circularId": 41467,
"submittedHow": "web"
},
"message_text": "Y. F. Liang, D. F. Hu (PMO, CAS), C. C. Jin (NAO, CAS) report on behalf of the Einstein Probe team:\n\nThe X-ray transient EP250821a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 41459). We report on the further results of WXT and FXT observations. The analysis of the WXT data shows that the event started at T0=2025-08-21T07:17:04 (UTC) and lasted for at least 80 s. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 7.33 x 10^20 cm^-2 and a photon index of 1.2 (-/+0.5). The derived average unabsorbed 0.5-4 keV flux is 1.3(-/+0.4) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.\n\nThe Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 320 s after T0. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 289.8862, DEC = -43.3808 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), within the WXT error circle. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.25 x 10^21 cm^-2 and a photon index around 3.5. The derived average unabsorbed 0.5-10 keV flux is about 2.6 x 10^(-10) erg/s/cm^2 during the time interval from 0 to 1000 seconds after the start of the observation.The results from FXT may have been affected by pile-up effect, particularly in the brightest time interval. Therefore, the values reported here should be considered preliminary and are intended to provide a rough estimate of the source intensity.\n\nLaunched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). ",
"published": "2025-08-21T16:27:14.109336Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-21T16:27:14.109358Z",
"modified": "2025-08-21T16:27:14.122818Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5771607,
"topic": "gcn.circulars",
"uuid": "1f4ba895-dfe3-483b-87d7-03238c065299",
"title": "EP250821a: Rapidly fading optical source detected in Las Cumbres followup",
"submitter": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"authors": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41470"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250821a",
"subject": "EP250821a: Rapidly fading optical source detected in Las Cumbres followup",
"createdOn": 1755795201978,
"submitter": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"circularId": 41470,
"submittedHow": "web"
},
"message_text": "Wenxiong Li (NAOC), Iair Arcavi (TAU), Ido Keinan (TAU), David Sand (U of Arizona)\nWe observed the position of EP250821a (Hu, Liang and Jin, GCN 41459; Liang, Hu and Jin, GCN 41467) with a Las Cumbres 1m telescope at Siding Spring Observatory 1.25 hours after the Einstein Probe WXT trigger and again 6.5 hours after the trigger. We took 2x300s exposures in each visit in the broad optical w band.\nWe find a rapidly fading source at RA=289.8853 Dec=-43.3813 (slightly offset from the position of the Swift counterpart; Dichara et al. GCN 41469) within the EP/FXT error circle and measure the following preliminary photometry calibrated to the r band:\nEpoch 1: MJD 60908.362 Mag 18.11 +- 0.03\nEpoch 2: MJD 60908.535 Mag 19.32 +- 0.02\nWe find a faint red likely extended source at this position in Legacy Survey data (https://www.legacysurvey.org/viewer).\nAddition followup is encouraged.",
"published": "2025-08-21T16:53:29.475286Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-21T16:53:29.475304Z",
"modified": "2025-08-21T16:53:29.486947Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776578,
"topic": "gcn.circulars",
"uuid": "9198a0b2-cc82-4aa9-8668-2022c9b82ed0",
"title": "EP250821a: Rapidly fading optical source detected in Las Cumbres followup",
"submitter": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"authors": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41470"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41470....1L",
"eventId": "EP250821a",
"subject": "EP250821a: Rapidly fading optical source detected in Las Cumbres followup",
"createdOn": 1755795201978,
"submitter": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"circularId": 41470,
"submittedHow": "web"
},
"message_text": "Wenxiong Li (NAOC), Iair Arcavi (TAU), Ido Keinan (TAU), David Sand (U of Arizona)\nWe observed the position of EP250821a (Hu, Liang and Jin, GCN 41459; Liang, Hu and Jin, GCN 41467) with a Las Cumbres 1m telescope at Siding Spring Observatory 1.25 hours after the Einstein Probe WXT trigger and again 6.5 hours after the trigger. We took 2x300s exposures in each visit in the broad optical w band.\nWe find a rapidly fading source at RA=289.8853 Dec=-43.3813 (slightly offset from the position of the Swift counterpart; Dichara et al. GCN 41469) within the EP/FXT error circle and measure the following preliminary photometry calibrated to the r band:\nEpoch 1: MJD 60908.362 Mag 18.11 +- 0.03\nEpoch 2: MJD 60908.535 Mag 19.32 +- 0.02\nWe find a faint red likely extended source at this position in Legacy Survey data (https://www.legacysurvey.org/viewer).\nAddition followup is encouraged.",
"published": "2025-09-08T08:08:41.522693Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:41.522711Z",
"modified": "2025-09-08T08:08:41.526889Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5781055,
"topic": "gcn.circulars",
"uuid": "e1c94687-224c-4236-a78a-11074a910e19",
"title": "EP250821a: SOAR observations",
"submitter": "James Freeburn at University of North Carolina at Chapel Hill <jamesfreeburn54@gmail.com>",
"authors": "James Freeburn at University of North Carolina at Chapel Hill <jamesfreeburn54@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41597"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41597....1F",
"eventId": "EP250821a",
"subject": "EP250821a: SOAR observations",
"createdOn": 1756495744892,
"submitter": "James Freeburn at University of North Carolina at Chapel Hill <jamesfreeburn54@gmail.com>",
"circularId": 41597,
"submittedHow": "web"
},
"message_text": "J. Freeburn (UNC), G. Srinivasaragavan (UMD), I. Andreoni (UNC), Anna Ho (Cornell)\n\nWe observed the location of the X-ray transient, EP250821a (Hu et al., GCN 41459) with the Goodman High Throughput Spectrograph mounted on the SOAR telescope in imaging mode (PI: Andreoni). We took two 300s exposures each in g, r and i-band between 2025-08-29T01:15:29 and 2025-08-29T01:43:27 UTC corresponding to ~8 days after the initial trigger.\n\nWith image subtraction using Legacy Survey images (Dey et al., 2019), we do not detect the optical counterpart associated with EP250821a (Dichiara et al., GCN 41469; Li et al., GCN 41470; Yao et al., GCN 41485; Oates et al., GCN 41491) and place the following 5-sigma AB magnitude upper limits:\n\ng > 22.9\nr > 22.9\ni > 22.8\n",
"published": "2025-09-22T08:08:52.589658Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:52.589667Z",
"modified": "2025-09-22T08:08:52.593210Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773731,
"topic": "gcn.circulars",
"uuid": "69461719-6fa1-4d1b-a8d5-7e952e6c678d",
"title": "EP250821a: SOAR observations",
"submitter": "James Freeburn at University of North Carolina at Chapel Hill <jamesfreeburn54@gmail.com>",
"authors": "James Freeburn at University of North Carolina at Chapel Hill <jamesfreeburn54@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41597"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250821a",
"subject": "EP250821a: SOAR observations",
"createdOn": 1756495744892,
"submitter": "James Freeburn at University of North Carolina at Chapel Hill <jamesfreeburn54@gmail.com>",
"circularId": 41597,
"submittedHow": "web"
},
"message_text": "J. Freeburn (UNC), G. Srinivasaragavan (UMD), I. Andreoni (UNC), Anna Ho (Cornell)\n\nWe observed the location of the X-ray transient, EP250821a (Hu et al., GCN 41459) with the Goodman High Throughput Spectrograph mounted on the SOAR telescope in imaging mode (PI: Andreoni). We took two 300s exposures each in g, r and i-band between 2025-08-29T01:15:29 and 2025-08-29T01:43:27 UTC corresponding to ~8 days after the initial trigger.\n\nWith image subtraction using Legacy Survey images (Dey et al., 2019), we do not detect the optical counterpart associated with EP250821a (Dichiara et al., GCN 41469; Li et al., GCN 41470; Yao et al., GCN 41485; Oates et al., GCN 41491) and place the following 5-sigma AB magnitude upper limits:\n\ng > 22.9\nr > 22.9\ni > 22.8\n",
"published": "2025-08-29T19:29:14.207619Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-29T19:29:14.207637Z",
"modified": "2025-08-29T19:29:14.217339Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776790,
"topic": "gcn.circulars",
"uuid": "3af72184-ceba-46d0-a05d-866afb9a5771",
"title": "EP250821a: SVOM/VT optical observation",
"submitter": "zhyao@bao.ac.cn",
"authors": "zhyao@bao.ac.cn",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41485"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41485....1Y",
"eventId": "EP250821a",
"subject": "EP250821a: SVOM/VT optical observation",
"createdOn": 1755832573660,
"submitter": "zhyao@bao.ac.cn",
"circularId": 41485,
"submittedHow": "web"
},
"message_text": "Z. H. Yao, Y. N. Ma, L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team.\n\nSVOM performed a Target of Opportunity observation of EP250821a detected by EP/WXT (Hu et al., GCN 41459). SVOM/VT began observing the field at 2025-08-21T11:23:41.5 UTC, 4.087 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.\n\nAn uncatalogued source is found using VT X-band data, within the error box of EP/FXT (Hu et al., GCN 41459; Liang et al., GCN 41467), Swift/XRT and UVOT (Dichiara et al., GCN 41469) and Las Cumbres (Li et al., GCN 41470) at R.A., Dec 289.88564, -43.38115 degrees:\n \nRA (J2000) = 19:19:32.55\nDec (J2000) = -43:22:52.14\n\nwith an uncertainty of 0.5 arcsec.\n \nThe source is detected in both VT_R and VT_B and was fading by ~0.5 mag between the first 2 VT observing sequences, the magnitudes are:\n \nT-T0 (h) | Exposure Time (s) | Band | Mag (AB) | Mag err\n--------------------|-------------------|------|----------|--------\n4.087 | 70 | VT_B | 19.44 | 0.12 \n4.087 | 70 | VT_R | 18.49 | 0.05\n6.363 | 70 | VT_B | 19.93 | 0.05 \n6.363 | 70 | VT_R | 19.02 | 0.03\n\nOur photometry was not corrected for Galactic extinction.\n\nThe Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.\n\n",
"published": "2025-09-08T08:09:01.591507Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:09:01.591524Z",
"modified": "2025-09-08T08:09:01.595737Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5771727,
"topic": "gcn.circulars",
"uuid": "f9bc08b4-fe48-4952-af98-1a1d21e53557",
"title": "EP250821a: SVOM/VT optical observation",
"submitter": "zhyao@bao.ac.cn",
"authors": "zhyao@bao.ac.cn",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41485"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250821a",
"subject": "EP250821a: SVOM/VT optical observation",
"createdOn": 1755832573660,
"submitter": "zhyao@bao.ac.cn",
"circularId": 41485,
"submittedHow": "web"
},
"message_text": "Z. H. Yao, Y. N. Ma, L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team.\n\nSVOM performed a Target of Opportunity observation of EP250821a detected by EP/WXT (Hu et al., GCN 41459). SVOM/VT began observing the field at 2025-08-21T11:23:41.5 UTC, 4.087 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.\n\nAn uncatalogued source is found using VT X-band data, within the error box of EP/FXT (Hu et al., GCN 41459; Liang et al., GCN 41467), Swift/XRT and UVOT (Dichiara et al., GCN 41469) and Las Cumbres (Li et al., GCN 41470) at R.A., Dec 289.88564, -43.38115 degrees:\n \nRA (J2000) = 19:19:32.55\nDec (J2000) = -43:22:52.14\n\nwith an uncertainty of 0.5 arcsec.\n \nThe source is detected in both VT_R and VT_B and was fading by ~0.5 mag between the first 2 VT observing sequences, the magnitudes are:\n \nT-T0 (h) | Exposure Time (s) | Band | Mag (AB) | Mag err\n--------------------|-------------------|------|----------|--------\n4.087 | 70 | VT_B | 19.44 | 0.12 \n4.087 | 70 | VT_R | 18.49 | 0.05\n6.363 | 70 | VT_B | 19.93 | 0.05 \n6.363 | 70 | VT_R | 19.02 | 0.03\n\nOur photometry was not corrected for Galactic extinction.\n\nThe Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.\n\n",
"published": "2025-08-22T03:16:21.576568Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-22T03:16:21.576586Z",
"modified": "2025-08-22T03:16:21.597345Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5771785,
"topic": "gcn.circulars",
"uuid": "c51674ed-ab5a-4c2f-bf14-f8c48c161b6b",
"title": "EP250821a: Swift/UVOT further observations.",
"submitter": "Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>",
"authors": "Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41491"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250821a",
"subject": "EP250821a: Swift/UVOT further observations.",
"createdOn": 1755855874730,
"submitter": "Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>",
"circularId": 41491,
"submittedHow": "email"
},
"message_text": "S. R. Oates (Lancaster U.) and S. Dichiara (PSU) report on \nbehalf of the Swift-XRT and Swift-UVOT team:\n\nSwift/UVOT has performed further follow-up observations of the Einstein\nProbe/WXT-detected source EP250821a (Hu et al., GCN 41459). The UVOT optical\ncounterpart reported in (Dichiara et al., GCN 41469) has faded, consistent\nwith the behaviour reported by Li et al. (GCN 41470) and Yao et al. (GCN 41485).\n\nThe refined UVOT position is\n\n RA (J2000) 19:19:32.56\n Dec (J2000) -43:22:52.3\n\nwith an estimated uncertainty of 0.5 arcsec (radius, 90% confidence). We note that\nthis position supersedes that reported in Dichiara et al. (GCN 41469), which\nis incorrect. We apologise for any confusion. \n\nPreliminary 3-sigma upper limits using the UVOT photometric system\n(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first\nfinding chart (FC) exposure and subsequent exposures are:\n\nFilter T_start(s) T_stop(s) Exp(s) Mag/3sigUL\n v 61584 72904 799 >19.9\n u 5186 11029 1897 18.88+\\-0.08 (reported in GCN 41469)\n u 68377 68575 195 >19.8\nuvw1 67966 68372 399 >20.0\nuvm2 67555 67961 399 >19.8\nuvw2 61180 72857 1168 >20.2\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.07 in the direction of the burst\n(Schlegel et al. 1998).\n\n\n",
"published": "2025-08-22T09:44:42.044900Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-22T09:44:42.044931Z",
"modified": "2025-08-22T09:44:42.182560Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776674,
"topic": "gcn.circulars",
"uuid": "5effa58b-ecfa-4cd1-aa69-0026128484b7",
"title": "EP250821a: Swift/UVOT further observations.",
"submitter": "Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>",
"authors": "Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41491"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41491....1O",
"eventId": "EP250821a",
"subject": "EP250821a: Swift/UVOT further observations.",
"createdOn": 1755855874730,
"submitter": "Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>",
"circularId": 41491,
"submittedHow": "email"
},
"message_text": "S. R. Oates (Lancaster U.) and S. Dichiara (PSU) report on \nbehalf of the Swift-XRT and Swift-UVOT team:\n\nSwift/UVOT has performed further follow-up observations of the Einstein\nProbe/WXT-detected source EP250821a (Hu et al., GCN 41459). The UVOT optical\ncounterpart reported in (Dichiara et al., GCN 41469) has faded, consistent\nwith the behaviour reported by Li et al. (GCN 41470) and Yao et al. (GCN 41485).\n\nThe refined UVOT position is\n\n RA (J2000) 19:19:32.56\n Dec (J2000) -43:22:52.3\n\nwith an estimated uncertainty of 0.5 arcsec (radius, 90% confidence). We note that\nthis position supersedes that reported in Dichiara et al. (GCN 41469), which\nis incorrect. We apologise for any confusion. \n\nPreliminary 3-sigma upper limits using the UVOT photometric system\n(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first\nfinding chart (FC) exposure and subsequent exposures are:\n\nFilter T_start(s) T_stop(s) Exp(s) Mag/3sigUL\n v 61584 72904 799 >19.9\n u 5186 11029 1897 18.88+\\-0.08 (reported in GCN 41469)\n u 68377 68575 195 >19.8\nuvw1 67966 68372 399 >20.0\nuvm2 67555 67961 399 >19.8\nuvw2 61180 72857 1168 >20.2\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.07 in the direction of the burst\n(Schlegel et al. 1998).\n\n\n",
"published": "2025-09-08T08:08:47.953943Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:47.953959Z",
"modified": "2025-09-08T08:08:47.957858Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776627,
"topic": "gcn.circulars",
"uuid": "a0696154-5d4b-4aec-adaa-4ca7fc4fabad",
"title": "EP250821a: Swift XRT and UVOT counterpart detection",
"submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"authors": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41469"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41469....1D",
"eventId": "EP250821a",
"subject": "EP250821a: Swift XRT and UVOT counterpart detection",
"createdOn": 1755793852423,
"submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"circularId": 41469,
"submittedHow": "email"
},
"message_text": "S. Dichiara (PSU), S. R. Oates (Lancaster U.), J.A. Kennea (PSU),\nK.L. Page (U. Leicester) report on behalf of the Swift-XRT and Swift-UVOT team:\n\nSwift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected\nsource EP250821a (Hu et al., GCN 41459), collecting 1.6 ks of Photon Counting (PC)\nmode data between T0+4.9 ks and T0+10 ks after the trigger. A likely counterpart has\nbeen found. The details of this source are:\n\n Source 1 (SWIFT J191932.6-432250):\n ==================================\n RA (J2000.0): 289.8861 = 19 19 32.66\n Dec (J2000.0): -43.3807 = -43 22 50.5\n Error:\t 3.6 (arcsec, radius, 90% confidence).\n Detect flag: GOOD\n Distance:\t 2.2 arcmin from the Einstein Probe/WXT position.\n Mean rate:\t 0.263 +/- 0.015 ct s^-1\n Mean flux:\t (9.44 +/- 0.53)e-12 erg cm^-2 s^-1\n Peak rate:\t 0.440 +/- 0.099 ct s^-1\n Peak flux:\t (1.58 +/- 0.35)e-11 erg cm^-2 s^-1\n ECF:\t 3.58e-11 erg cm^-2 ct^-1\n\t\t assuming NH=1.38e+21 cm^-2, gamma=1.93\n\t\t determined from a spectral fit.\n XMM UL:\t 5.5e-12 erg cm^-2 s^-1, (0.3-10 keV)\n\t\t so the source is 2.9-sigma above this 3-sigma upper limit.\n The source may be fading, at the 1.1-sigma level.\n\n\nAll fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with\ncatalogues and upper limits from other missions, we assumed a power-law spectrum\nwith NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.\n\nThe results of the XRT-team automatic analysis of the XRT observations, including a\nposition-specific upper limit calculator, are available at\nhttps://www.swift.ac.uk/EP/EP_FIELD00059.\n\nSource 1 was also detected in the UVOT u-band image. The preliminary UVOT position\nis:\n RA (J2000.0): 289.883 =\t19 19 31.86\n Dec (J2000.0): -43.3816 = -43 22 53.8\n\n\nPreliminary detection u-band magnitude in 1897 s exposure is 18.88 +/- 0.08, using\nthe UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373)\n\nWe note that the source is also listed in the Guide Star Catalog (Lasker et al,\n2008) and\nit has clearly brightened from its catalogued brightness (Bmag = 22.3).\n\nThis circular is an official product of the Swift XRT and UVOT team.\n\n",
"published": "2025-09-08T08:08:45.350110Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:45.350129Z",
"modified": "2025-09-08T08:08:45.354819Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5771604,
"topic": "gcn.circulars",
"uuid": "f6dcab86-758f-4bd8-867d-a7c42b35a083",
"title": "EP250821a: Swift XRT and UVOT counterpart detection",
"submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"authors": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41469"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250821a",
"subject": "EP250821a: Swift XRT and UVOT counterpart detection",
"createdOn": 1755793852423,
"submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"circularId": 41469,
"submittedHow": "email"
},
"message_text": "S. Dichiara (PSU), S. R. Oates (Lancaster U.), J.A. Kennea (PSU),\nK.L. Page (U. Leicester) report on behalf of the Swift-XRT and Swift-UVOT team:\n\nSwift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected\nsource EP250821a (Hu et al., GCN 41459), collecting 1.6 ks of Photon Counting (PC)\nmode data between T0+4.9 ks and T0+10 ks after the trigger. A likely counterpart has\nbeen found. The details of this source are:\n\n Source 1 (SWIFT J191932.6-432250):\n ==================================\n RA (J2000.0): 289.8861 = 19 19 32.66\n Dec (J2000.0): -43.3807 = -43 22 50.5\n Error:\t 3.6 (arcsec, radius, 90% confidence).\n Detect flag: GOOD\n Distance:\t 2.2 arcmin from the Einstein Probe/WXT position.\n Mean rate:\t 0.263 +/- 0.015 ct s^-1\n Mean flux:\t (9.44 +/- 0.53)e-12 erg cm^-2 s^-1\n Peak rate:\t 0.440 +/- 0.099 ct s^-1\n Peak flux:\t (1.58 +/- 0.35)e-11 erg cm^-2 s^-1\n ECF:\t 3.58e-11 erg cm^-2 ct^-1\n\t\t assuming NH=1.38e+21 cm^-2, gamma=1.93\n\t\t determined from a spectral fit.\n XMM UL:\t 5.5e-12 erg cm^-2 s^-1, (0.3-10 keV)\n\t\t so the source is 2.9-sigma above this 3-sigma upper limit.\n The source may be fading, at the 1.1-sigma level.\n\n\nAll fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with\ncatalogues and upper limits from other missions, we assumed a power-law spectrum\nwith NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.\n\nThe results of the XRT-team automatic analysis of the XRT observations, including a\nposition-specific upper limit calculator, are available at\nhttps://www.swift.ac.uk/EP/EP_FIELD00059.\n\nSource 1 was also detected in the UVOT u-band image. The preliminary UVOT position\nis:\n RA (J2000.0): 289.883 =\t19 19 31.86\n Dec (J2000.0): -43.3816 = -43 22 53.8\n\n\nPreliminary detection u-band magnitude in 1897 s exposure is 18.88 +/- 0.08, using\nthe UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373)\n\nWe note that the source is also listed in the Guide Star Catalog (Lasker et al,\n2008) and\nit has clearly brightened from its catalogued brightness (Bmag = 22.3).\n\nThis circular is an official product of the Swift XRT and UVOT team.\n\n",
"published": "2025-08-21T16:30:53.796045Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-21T16:30:53.796078Z",
"modified": "2025-08-21T16:30:53.824763Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776791,
"topic": "gcn.circulars",
"uuid": "e8e83a00-1b8f-44cd-9b2b-74a608e8b73c",
"title": "EP250821a: Swift/XRT counterpart fading",
"submitter": "Simone Dichiara at Pennsylvania State University <sbd5667@psu.edu>",
"authors": "Simone Dichiara at Pennsylvania State University <sbd5667@psu.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41496"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41496....1D",
"eventId": "EP250821a",
"subject": "EP250821a: Swift/XRT counterpart fading",
"createdOn": 1755873697621,
"submitter": "Simone Dichiara at Pennsylvania State University <sbd5667@psu.edu>",
"circularId": 41496,
"submittedHow": "web"
},
"message_text": "\nS. Dichiara (PSU), S. R. Oates (Lancaster U.), J.A. Kennea (PSU), K.L. Page (U. Leicester) report on behalf of the Swift-XRT and Swift-UVOT team:\n\nSwift-XRT has performed further follow-up observations of the EP-WXT transient EP250821a (Hu et al., GCN 41459), collecting a total of 3.0 ks of Photon Counting (PC) mode data between T0+61.0 ks and T0+72.9 ks. \n\nThe source detected in XRT in the first 1.9 ks of data previously reported as “Source 1” (Dichiara et al., GCN 41469), consistent with the optical counterpart (Li et al., GCN 41470, Yao et al., GCN 41485, An et al., GCN 41490), has faded more than 3 sigma in the latest X-ray observation.\nThe count rate derived from the follow-up observation is 2.2 (+/-0.3) x 10^-2 cts/s.\nThe light curve can be modelled with a power-law decay with an index of alpha=1.03 +/- 0.07. \n\nA spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.0 +/- 0.2. The best-fitting absorption column is 1.4 (+0.7, -0.6) x 10^21 cm^-2 , in excess of the Galactic value of 7.26 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.51 x 10^-11 (4.48 x 10^-11) erg cm^-2 count^-1. The observed (unabsorbed) flux obtained from the follow-up observations from T0+61.0 ks to T0+72.9 ks is thus 7.7 x 10^-13 (9.9 x 10^-12) erg cm^-2 s^-1. \n\nThe results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/EP/EP_FIELD00059/\n\nThis circular is an official product of the Swift-XRT team.",
"published": "2025-09-08T08:09:01.603970Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:09:01.603987Z",
"modified": "2025-09-08T08:09:01.608069Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5771837,
"topic": "gcn.circulars",
"uuid": "58578681-e92c-41b5-80dd-4614c1c050dc",
"title": "EP250821a: Swift/XRT counterpart fading",
"submitter": "Simone Dichiara at Pennsylvania State University <sbd5667@psu.edu>",
"authors": "Simone Dichiara at Pennsylvania State University <sbd5667@psu.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41496"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250821a",
"subject": "EP250821a: Swift/XRT counterpart fading",
"createdOn": 1755873697621,
"submitter": "Simone Dichiara at Pennsylvania State University <sbd5667@psu.edu>",
"circularId": 41496,
"submittedHow": "web"
},
"message_text": "\nS. Dichiara (PSU), S. R. Oates (Lancaster U.), J.A. Kennea (PSU), K.L. Page (U. Leicester) report on behalf of the Swift-XRT and Swift-UVOT team:\n\nSwift-XRT has performed further follow-up observations of the EP-WXT transient EP250821a (Hu et al., GCN 41459), collecting a total of 3.0 ks of Photon Counting (PC) mode data between T0+61.0 ks and T0+72.9 ks. \n\nThe source detected in XRT in the first 1.9 ks of data previously reported as “Source 1” (Dichiara et al., GCN 41469), consistent with the optical counterpart (Li et al., GCN 41470, Yao et al., GCN 41485, An et al., GCN 41490), has faded more than 3 sigma in the latest X-ray observation.\nThe count rate derived from the follow-up observation is 2.2 (+/-0.3) x 10^-2 cts/s.\nThe light curve can be modelled with a power-law decay with an index of alpha=1.03 +/- 0.07. \n\nA spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.0 +/- 0.2. The best-fitting absorption column is 1.4 (+0.7, -0.6) x 10^21 cm^-2 , in excess of the Galactic value of 7.26 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.51 x 10^-11 (4.48 x 10^-11) erg cm^-2 count^-1. The observed (unabsorbed) flux obtained from the follow-up observations from T0+61.0 ks to T0+72.9 ks is thus 7.7 x 10^-13 (9.9 x 10^-12) erg cm^-2 s^-1. \n\nThe results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/EP/EP_FIELD00059/\n\nThis circular is an official product of the Swift-XRT team.",
"published": "2025-08-22T14:41:38.049265Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-22T14:41:38.049282Z",
"modified": "2025-08-22T14:41:38.060276Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5771778,
"topic": "gcn.circulars",
"uuid": "803edd8e-f2f3-4ee5-8678-e01c91b54067",
"title": "EP250821a: VLT X-shooter spectroscopic redshift z = 0.577",
"submitter": "nrt3@le.ac.uk",
"authors": "nrt3@le.ac.uk",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41490"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250821a",
"subject": "EP250821a: VLT X-shooter spectroscopic redshift z = 0.577",
"createdOn": 1755853318990,
"submitter": "nrt3@le.ac.uk",
"circularId": 41490,
"submittedHow": "web"
},
"message_text": "J. An (NAOC), V. Abril-Melgarejo (LUX-Paris Obs.), R. A. J. Eyles-Ferris (U. Leicester), D. Xu (NAOC), A. L. Thakur (INAF-IAPS), A. J. Levan (Radboud U.), P. G. Jonker (Radboud U.), D. B. Malesani (DAWN/NBI and Radboud), S. R. Oates (U. Lancaster), G. Corcoran (UCD), A. Martin-Carrillo (UCD), V. D’Elia (ASI/SSDC), N. R. Tanvir (U. Leicester) report on behalf of the Stargate collaboration:\n\nWe observed the location of the optical counterpart and coincident likely host galaxy (Dichiara et al., GCN 41469; Li et al. GCN 41470; Yao et al. GCN 41485) of the X-ray transient EP250821a detected by Einstein Probe (Hu et al. GCN 41459; Liang et al., GCN 41467), using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph.\n\nOur spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 600 s each. Observations started on 2025-08-22 at approximately 04:10 UT (20.9 hr after the EP trigger). In a preliminary reduction of the spectra, we detect absorption lines of Fe II (fine structure), Mg II, Ca II, Na I, and emission lines of [O II], [O III], H alpha, H beta, H gamma, [N II], [S II], from which we infer a redshift of z = 0.577. We note that our spectroscopic redshift measurement is roughly consistent with the photometric redshift value of 0.64 +/- 0.06 provided for the catalogued object in Legacy Survey that was noted by Li et al. (GCN 41470).\n\nFrom the X-shooter acquisition imaging we estimate a magnitude of r = 20.9 at 2025-08-22 03:41 UT, approximately 20.4 hr post-trigger. Given the Legacy Survey host magnitude of r = 21.79 +/- 0.02, this suggests a significant transient contribution at this epoch.\n\nWe acknowledge excellent support from the ESO observing staff in Paranal, in particular Celia Desgrange, Lorena Faundez, Camila de Sa Freitas. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).\n",
"published": "2025-08-22T09:02:08.023532Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-22T09:02:08.023553Z",
"modified": "2025-08-22T09:02:08.041595Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776807,
"topic": "gcn.circulars",
"uuid": "2ecd83b8-af37-438e-8f1f-7fc036ed6f56",
"title": "EP250821a: VLT X-shooter spectroscopic redshift z = 0.577",
"submitter": "nrt3@le.ac.uk",
"authors": "nrt3@le.ac.uk",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41490"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41490....1A",
"eventId": "EP250821a",
"subject": "EP250821a: VLT X-shooter spectroscopic redshift z = 0.577",
"createdOn": 1755853318990,
"submitter": "nrt3@le.ac.uk",
"circularId": 41490,
"submittedHow": "web"
},
"message_text": "J. An (NAOC), V. Abril-Melgarejo (LUX-Paris Obs.), R. A. J. Eyles-Ferris (U. Leicester), D. Xu (NAOC), A. L. Thakur (INAF-IAPS), A. J. Levan (Radboud U.), P. G. Jonker (Radboud U.), D. B. Malesani (DAWN/NBI and Radboud), S. R. Oates (U. Lancaster), G. Corcoran (UCD), A. Martin-Carrillo (UCD), V. D’Elia (ASI/SSDC), N. R. Tanvir (U. Leicester) report on behalf of the Stargate collaboration:\n\nWe observed the location of the optical counterpart and coincident likely host galaxy (Dichiara et al., GCN 41469; Li et al. GCN 41470; Yao et al. GCN 41485) of the X-ray transient EP250821a detected by Einstein Probe (Hu et al. GCN 41459; Liang et al., GCN 41467), using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph.\n\nOur spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 600 s each. Observations started on 2025-08-22 at approximately 04:10 UT (20.9 hr after the EP trigger). In a preliminary reduction of the spectra, we detect absorption lines of Fe II (fine structure), Mg II, Ca II, Na I, and emission lines of [O II], [O III], H alpha, H beta, H gamma, [N II], [S II], from which we infer a redshift of z = 0.577. We note that our spectroscopic redshift measurement is roughly consistent with the photometric redshift value of 0.64 +/- 0.06 provided for the catalogued object in Legacy Survey that was noted by Li et al. (GCN 41470).\n\nFrom the X-shooter acquisition imaging we estimate a magnitude of r = 20.9 at 2025-08-22 03:41 UT, approximately 20.4 hr post-trigger. Given the Legacy Survey host magnitude of r = 21.79 +/- 0.02, this suggests a significant transient contribution at this epoch.\n\nWe acknowledge excellent support from the ESO observing staff in Paranal, in particular Celia Desgrange, Lorena Faundez, Camila de Sa Freitas. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).\n",
"published": "2025-09-08T08:09:01.801440Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:09:01.801454Z",
"modified": "2025-09-08T08:09:01.805269Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5780992,
"topic": "gcn.circulars",
"uuid": "ba5ef763-1d6f-4e3d-b3f2-2adad2a05ea9",
"title": "EP250827a and EP250827b: Upper limit from Fermi-GBM Observations",
"submitter": "mariaedvige.ravasio@ru.nl",
"authors": "mariaedvige.ravasio@ru.nl",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41708"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41708....1R",
"eventId": "EP250827a",
"subject": "EP250827a and EP250827b: Upper limit from Fermi-GBM Observations",
"createdOn": 1757009889622,
"submitter": "mariaedvige.ravasio@ru.nl",
"circularId": 41708,
"submittedHow": "web"
},
"message_text": "M. E. Ravasio and P.G. Jonker (Radboud Univ.) on behalf of the Einstein Probe Team\nand\nE. Burns (LSU), C. M. Hui (NASA MSFC) and R. Hamburg (USRA) on behalf of the Fermi-GBM Team, report:\n\nFermi-GBM had full spatial coverage of the transients EP250827a (Hua et al., GCN 41553, Ni et al., GCN 41573) and EP250827b (Schroeder et al., GCN 41635) detected by EP-WXT. There was no Fermi-GBM onboard trigger around both EP trigger times (T0=2025-08-27T07:39:01 UTC for EP250827a, and T0=2025-08-27T06:22:27 UTC for EP250827b).\n\nThe GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [T0-50; T0+500] s, seeking signals between 64 ms and 32.768 s in duration. No signal consistent with the EP transients, both temporally and spatially, is identified, as confirmed also by visual inspection of the data.\n\nAssuming a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7), and a duration of 8.192 s, we derive a flux upper limit of 3.5e-08 erg/cm2/s for EP250827a, and a flux upper limit of 3.0e-08 erg/cm2/s for EP250827b, in the energy band 10-1000 keV.\n[1] Goldstein et al. 2019 arXiv:1903.12597",
"published": "2025-09-22T08:08:49.931170Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:49.931177Z",
"modified": "2025-09-22T08:08:49.934609Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5775629,
"topic": "gcn.circulars",
"uuid": "e02de78b-ae0e-4733-98e7-0599e26b083f",
"title": "EP250827a and EP250827b: Upper limit from Fermi-GBM Observations",
"submitter": "mariaedvige.ravasio@ru.nl",
"authors": "mariaedvige.ravasio@ru.nl",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41708"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a and EP250827b: Upper limit from Fermi-GBM Observations",
"createdOn": 1757009889622,
"submitter": "mariaedvige.ravasio@ru.nl",
"circularId": 41708,
"submittedHow": "web"
},
"message_text": "M. E. Ravasio and P.G. Jonker (Radboud Univ.) on behalf of the Einstein Probe Team\nand\nE. Burns (LSU), C. M. Hui (NASA MSFC) and R. Hamburg (USRA) on behalf of the Fermi-GBM Team, report:\n\nFermi-GBM had full spatial coverage of the transients EP250827a (Hua et al., GCN 41553, Ni et al., GCN 41573) and EP250827b (Schroeder et al., GCN 41635) detected by EP-WXT. There was no Fermi-GBM onboard trigger around both EP trigger times (T0=2025-08-27T07:39:01 UTC for EP250827a, and T0=2025-08-27T06:22:27 UTC for EP250827b).\n\nThe GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [T0-50; T0+500] s, seeking signals between 64 ms and 32.768 s in duration. No signal consistent with the EP transients, both temporally and spatially, is identified, as confirmed also by visual inspection of the data.\n\nAssuming a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7), and a duration of 8.192 s, we derive a flux upper limit of 3.5e-08 erg/cm2/s for EP250827a, and a flux upper limit of 3.0e-08 erg/cm2/s for EP250827b, in the energy band 10-1000 keV.\n[1] Goldstein et al. 2019 arXiv:1903.12597",
"published": "2025-09-04T18:18:18.056461Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-04T18:18:18.056484Z",
"modified": "2025-09-04T18:18:18.066399Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776719,
"topic": "gcn.circulars",
"uuid": "621566c6-ee1b-48ee-abf6-5bb636467aab",
"title": "EP250827A: An optical rebrightening was detected by LCO.",
"submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"authors": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41564"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41564....1G",
"eventId": "EP250827a",
"subject": "EP250827A: An optical rebrightening was detected by LCO.",
"createdOn": 1756308977636,
"submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"circularId": 41564,
"submittedHow": "web"
},
"message_text": "Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration.\n \nWe observed the field of the EP 250827A triggered by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hua et al., GCN 41553) in the r, V filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Siding Spring is near Coonabarabran, New South Wales, Australia . The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel).\n\nObservations began on August 27, 2025, starting 5.135 hours after the GRB trigger. Further observations are currently ongoing.\n\nWe clearly detect the optical transient (OT) reported by GCNs (Levan et al., GCN 41554; Li et al., GCN 41555; Lipunov et al., GCN 41558; Gritsevich et al., GCN 41559, An et al., GCN 41660) in our r band image. A brightening of ≈ 0.5 mag was observed within 1–5 hours after the burst, with An et al,. GCN 41660, reported a magnitude of 18.9 mag at ~1 hour post-burst.\n\n\n|Date|\t\t|UTstart|\t|t-T0 (hours)|\t|Exp (sec)|\t|Filter|\t|Magnitude| \n-------------------------------------------------------------------------------------------------- \n2025-08-27\t12:48:48.96\t5.135\t\t1 x 900 \tr\t r = 18.44 +/- 0.01\n\nThe field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.\n",
"published": "2025-09-08T08:08:49.576883Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:49.576898Z",
"modified": "2025-09-08T08:08:49.580891Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773108,
"topic": "gcn.circulars",
"uuid": "c333607d-12f3-48a1-aaf7-ea09b4ea8d10",
"title": "EP250827A: An optical rebrightening was detected by LCO.",
"submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"authors": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41564"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827A: An optical rebrightening was detected by LCO.",
"createdOn": 1756308977636,
"submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"circularId": 41564,
"submittedHow": "web"
},
"message_text": "Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration.\n \nWe observed the field of the EP 250827A triggered by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hua et al., GCN 41553) in the r, V filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Siding Spring is near Coonabarabran, New South Wales, Australia . The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel).\n\nObservations began on August 27, 2025, starting 5.135 hours after the GRB trigger. Further observations are currently ongoing.\n\nWe clearly detect the optical transient (OT) reported by GCNs (Levan et al., GCN 41554; Li et al., GCN 41555; Lipunov et al., GCN 41558; Gritsevich et al., GCN 41559, An et al., GCN 41660) in our r band image. A brightening of ≈ 0.5 mag was observed within 1–5 hours after the burst, with An et al,. GCN 41660, reported a magnitude of 18.9 mag at ~1 hour post-burst.\n\n\n|Date|\t\t|UTstart|\t|t-T0 (hours)|\t|Exp (sec)|\t|Filter|\t|Magnitude| \n-------------------------------------------------------------------------------------------------- \n2025-08-27\t12:48:48.96\t5.135\t\t1 x 900 \tr\t r = 18.44 +/- 0.01\n\nThe field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.\n",
"published": "2025-08-27T15:36:18.535645Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T15:36:18.535662Z",
"modified": "2025-08-27T15:36:18.546363Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776825,
"topic": "gcn.circulars",
"uuid": "bd162bd8-8d67-4818-840c-bfffd47b6f21",
"title": "EP250827a: BOOTES-7 early optical dectection",
"submitter": "I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg@iaa.es>",
"authors": "I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg@iaa.es>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41559"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41559....1G",
"eventId": "EP250827a",
"subject": "EP250827a: BOOTES-7 early optical dectection",
"createdOn": 1756290100481,
"submitter": "I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg@iaa.es>",
"circularId": 41559,
"submittedHow": "web"
},
"message_text": "M. Gritsevich (Univ. of Helsinki), I. Perez-Garcia, E. Fernandez-Garcia, S.-Y. Wu, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar (Univ. of Malaga), D.-R. Xiong (YNAO, Kumming), Y.-D. Hu (GXU, Guanxi), B.-B. Zhang (Nanjing Univ.), and A. Maury (Space Obs., San Pedro de Atacama), on behalf of a larger collaboration, report:\n\nFollowing the detection of EP250827a by Einstein Probe (Hua et al., GCNC 41553), the 0.6m BOOTES-7 robotic telescope at Space Observatory (San Pedro de Atacama, Chile) automatically observed the X-ray transient location starting on Aug. 27, 07:47:36 UT (i.e. 413 s after trigger). A series of images in clear filter were gathered for 2 h and the optical counterpart reported by Levan et al. (GCNC 41554), Li et al. (GCNC 41555) and Lipunov et al. (GCNC 41558) was detected at early times in our dataset. We measure a magnitude of 18.67 +/- 0.05 on a co-added image (60s x 5 exposures) at 07:53:11 UT mid time. Further data analysis is ongoing.\n\nWe would like to thank the staff at San Pedro de Atacama Space Observatory for their excellent support.",
"published": "2025-09-08T08:09:03.045203Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:09:03.045219Z",
"modified": "2025-09-08T08:09:03.049320Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773050,
"topic": "gcn.circulars",
"uuid": "d264266e-d347-462c-a95e-3881ccd21eef",
"title": "EP250827a: BOOTES-7 early optical dectection",
"submitter": "I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg@iaa.es>",
"authors": "I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg@iaa.es>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41559"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: BOOTES-7 early optical dectection",
"createdOn": 1756290100481,
"submitter": "I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg@iaa.es>",
"circularId": 41559,
"submittedHow": "web"
},
"message_text": "M. Gritsevich (Univ. of Helsinki), I. Perez-Garcia, E. Fernandez-Garcia, S.-Y. Wu, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar (Univ. of Malaga), D.-R. Xiong (YNAO, Kumming), Y.-D. Hu (GXU, Guanxi), B.-B. Zhang (Nanjing Univ.), and A. Maury (Space Obs., San Pedro de Atacama), on behalf of a larger collaboration, report:\n\nFollowing the detection of EP250827a by Einstein Probe (Hua et al., GCNC 41553), the 0.6m BOOTES-7 robotic telescope at Space Observatory (San Pedro de Atacama, Chile) automatically observed the X-ray transient location starting on Aug. 27, 07:47:36 UT (i.e. 413 s after trigger). A series of images in clear filter were gathered for 2 h and the optical counterpart reported by Levan et al. (GCNC 41554), Li et al. (GCNC 41555) and Lipunov et al. (GCNC 41558) was detected at early times in our dataset. We measure a magnitude of 18.67 +/- 0.05 on a co-added image (60s x 5 exposures) at 07:53:11 UT mid time. Further data analysis is ongoing.\n\nWe would like to thank the staff at San Pedro de Atacama Space Observatory for their excellent support.",
"published": "2025-08-27T10:21:48.625013Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T10:21:48.625028Z",
"modified": "2025-08-27T10:21:48.638284Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776682,
"topic": "gcn.circulars",
"uuid": "ccd0180c-eafb-455c-8dc0-2fdef3c92420",
"title": "EP250827a: confirmation of optical rebrightening with LCO",
"submitter": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
"authors": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
"data": {
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"bibcode": "2025GCN.41568....1P",
"eventId": "EP250827a",
"subject": "EP250827a: confirmation of optical rebrightening with LCO",
"createdOn": 1756317877542,
"submitter": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
"circularId": 41568,
"submittedHow": "web"
},
"message_text": "I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL)\n\nWe observed the field of EP250827a, detected by Einstein Probe (Hua et al. GCN 41553) and Swift-XRT \n(Evans et al. GCN 41563) at a redshift of z = 1.613 (Levan et al. GCN 41557) with one of the three 1-m telescopes of the Las Cumbres Observatory Global Telescope network (LCO) equipped with Sinistro cameras located at the LCO node at the Cerro Tololo Inter-American Observatory (CTIO), Chile. The observation, of 300 seconds in the SDSS-r filter, started at 2025-08-27 10:04:04 UT, about 2.39 hours after the EP trigger. We detect clearly a source within the EP-FXT and Swift-XRT error circles at a position consistent with the detections reported by Levan et al. (GCN 41554) and Li et al. (GCN 41555) and with other optical detections reported by Lipunov et al., GCN 41558; Gritsevich et al., GCN 41559; An et al., GCN 41560, Ghosh et al., GCN 41564; and O'Neill GCN 41567). We measure a magnitude of r = 18.65 +/- 0.04, calibrated with the Legacy Surveys DR10 catalog and not corrected for Galactic extinction. Using a similar r-band filter, we confirm the optical rebrightening detected also by Ghosh et al. (GCN 41564) between the TRT observation (r = 18.93 +/- 0.03, 0.86 hours after the EP trigger) and our LCO observation (r = 18.65 +/- 0.04, 2.39 hours after the EP trigger).\n\n\nThis work makes use of observations from the Las Cumbres Observatory global telescope network program IAC2025B-008 (SGLF).\n\n",
"published": "2025-09-08T08:08:48.084537Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:48.084554Z",
"modified": "2025-09-08T08:08:48.088722Z",
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},
{
"id": 5773135,
"topic": "gcn.circulars",
"uuid": "0f014afd-8a91-48a4-bd44-2d0d6300a3a1",
"title": "EP250827a: confirmation of optical rebrightening with LCO",
"submitter": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
"authors": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
"data": {
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"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: confirmation of optical rebrightening with LCO",
"createdOn": 1756317877542,
"submitter": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
"circularId": 41568,
"submittedHow": "web"
},
"message_text": "I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL)\n\nWe observed the field of EP250827a, detected by Einstein Probe (Hua et al. GCN 41553) and Swift-XRT \n(Evans et al. GCN 41563) at a redshift of z = 1.613 (Levan et al. GCN 41557) with one of the three 1-m telescopes of the Las Cumbres Observatory Global Telescope network (LCO) equipped with Sinistro cameras located at the LCO node at the Cerro Tololo Inter-American Observatory (CTIO), Chile. The observation, of 300 seconds in the SDSS-r filter, started at 2025-08-27 10:04:04 UT, about 2.39 hours after the EP trigger. We detect clearly a source within the EP-FXT and Swift-XRT error circles at a position consistent with the detections reported by Levan et al. (GCN 41554) and Li et al. (GCN 41555) and with other optical detections reported by Lipunov et al., GCN 41558; Gritsevich et al., GCN 41559; An et al., GCN 41560, Ghosh et al., GCN 41564; and O'Neill GCN 41567). We measure a magnitude of r = 18.65 +/- 0.04, calibrated with the Legacy Surveys DR10 catalog and not corrected for Galactic extinction. Using a similar r-band filter, we confirm the optical rebrightening detected also by Ghosh et al. (GCN 41564) between the TRT observation (r = 18.93 +/- 0.03, 0.86 hours after the EP trigger) and our LCO observation (r = 18.65 +/- 0.04, 2.39 hours after the EP trigger).\n\n\nThis work makes use of observations from the Las Cumbres Observatory global telescope network program IAC2025B-008 (SGLF).\n\n",
"published": "2025-08-27T18:04:46.723861Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T18:04:46.723880Z",
"modified": "2025-08-27T18:04:46.741091Z",
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},
{
"id": 5776718,
"topic": "gcn.circulars",
"uuid": "9d8e9931-b9d5-4712-97d9-5555605df527",
"title": "EP250827a: Einstein Probe detection of an X-ray transient",
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"authors": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"data": {
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"bibcode": "2025GCN.41553....1H",
"eventId": "EP250827a",
"subject": "EP250827a: Einstein Probe detection of an X-ray transient",
"createdOn": 1756283547624,
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"circularId": 41553,
"submittedHow": "web"
},
"message_text": "Y. L. Hua (PMO,CAS), K. R. Ni (CCNU) , M. J. Liu and C. C. Jin (NAO,CAS) on behalf of the Einstein Probe (EP) team:\n\nWe report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250827a. The transient triggered EP-WXT (ID: 01709200787) at 2025-08-27T07:40:43 (UTC). The WXT position of the source is R.A. = 3.488 deg, DEC = -56.463 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).\n\nA follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 3.46915 deg, DEC = -56.4998 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).\n\nFurther information will be updated when the telemetry data is received.\n\nLaunched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).",
"published": "2025-09-08T08:08:49.565460Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:49.565476Z",
"modified": "2025-09-08T08:08:49.569445Z",
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},
{
"id": 5773019,
"topic": "gcn.circulars",
"uuid": "c7585940-3d5f-4871-9d94-71e248327ef4",
"title": "EP250827a: Einstein Probe detection of an X-ray transient",
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"authors": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41553"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: Einstein Probe detection of an X-ray transient",
"createdOn": 1756283547624,
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"circularId": 41553,
"submittedHow": "web"
},
"message_text": "Y. L. Hua (PMO,CAS), K. R. Ni (CCNU) , M. J. Liu and C. C. Jin (NAO,CAS) on behalf of the Einstein Probe (EP) team:\n\nWe report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250827a. The transient triggered EP-WXT (ID: 01709200787) at 2025-08-27T07:40:43 (UTC). The WXT position of the source is R.A. = 3.488 deg, DEC = -56.463 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).\n\nA follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 3.46915 deg, DEC = -56.4998 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).\n\nFurther information will be updated when the telemetry data is received.\n\nLaunched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).",
"published": "2025-08-27T08:32:35.059306Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T08:32:35.059324Z",
"modified": "2025-08-27T08:32:35.064711Z",
"nonlocalizedevents": [],
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},
{
"id": 5773022,
"topic": "gcn.circulars",
"uuid": "979ca3ee-04e2-4897-a295-b20066d4ff4a",
"title": "EP250827a: Gemini-South optical counterpart detection",
"submitter": "Andrew Levan at Radboud University <a.levan@astro.ru.nl>",
"authors": "Andrew Levan at Radboud University <a.levan@astro.ru.nl>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41554"
},
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"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: Gemini-South optical counterpart detection",
"createdOn": 1756284262601,
"submitter": "Andrew Levan at Radboud University <a.levan@astro.ru.nl>",
"circularId": 41554,
"submittedHow": "web"
},
"message_text": "A. J. Levan (Radboud and Warwick), J. A. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (Leicester), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), report on behalf of a larger collaboration:\n\nWe observed the location of EP250827a (Hua et al. GCN 41553) with Gemini-South and the GMOS instrument. Observations began at 08:14 UT approximately 34 minutes after the EP trigger time. Within the WXT and FXT error circles we locate a new source in our first r-band exposure with a location of \n\nRA(J2000): 00:13:52.32\nDEC(J2000) -56:29:52.9\n\nThe error is about 0.3\" in each coordinate. The source is not visible in the Legacy Survey and has a magnitude of r = 18.70 +- 0.02 (calibrated against nearby stars from the SkyMapper catalog and not corrected for Galactic extinction). This is very likely the optical counterpart of EP250827a.\n\nWe thank the staff of Gemini for their outstanding work in rapidly obtaining these observations. \n",
"published": "2025-08-27T08:44:29.071828Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T08:44:29.071844Z",
"modified": "2025-08-27T08:44:29.099907Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776816,
"topic": "gcn.circulars",
"uuid": "8adc8ece-30c0-42c6-8c1f-65125af18653",
"title": "EP250827a: Gemini-South optical counterpart detection",
"submitter": "Andrew Levan at Radboud University <a.levan@astro.ru.nl>",
"authors": "Andrew Levan at Radboud University <a.levan@astro.ru.nl>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41554"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41554....1L",
"eventId": "EP250827a",
"subject": "EP250827a: Gemini-South optical counterpart detection",
"createdOn": 1756284262601,
"submitter": "Andrew Levan at Radboud University <a.levan@astro.ru.nl>",
"circularId": 41554,
"submittedHow": "web"
},
"message_text": "A. J. Levan (Radboud and Warwick), J. A. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (Leicester), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), report on behalf of a larger collaboration:\n\nWe observed the location of EP250827a (Hua et al. GCN 41553) with Gemini-South and the GMOS instrument. Observations began at 08:14 UT approximately 34 minutes after the EP trigger time. Within the WXT and FXT error circles we locate a new source in our first r-band exposure with a location of \n\nRA(J2000): 00:13:52.32\nDEC(J2000) -56:29:52.9\n\nThe error is about 0.3\" in each coordinate. The source is not visible in the Legacy Survey and has a magnitude of r = 18.70 +- 0.02 (calibrated against nearby stars from the SkyMapper catalog and not corrected for Galactic extinction). This is very likely the optical counterpart of EP250827a.\n\nWe thank the staff of Gemini for their outstanding work in rapidly obtaining these observations. \n",
"published": "2025-09-08T08:09:02.926444Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:09:02.926466Z",
"modified": "2025-09-08T08:09:02.930802Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776824,
"topic": "gcn.circulars",
"uuid": "9327cc9e-a033-4122-aa83-d103233074f0",
"title": "EP250827a: Gemini-South redshift z = 1.613",
"submitter": "Jonathan Quirola at Radboud University <jaquirola1990@gmail.com>",
"authors": "Jonathan Quirola at Radboud University <jaquirola1990@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41557"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41557....1L",
"eventId": "EP250827a",
"subject": "EP250827a: Gemini-South redshift z = 1.613",
"createdOn": 1756286655467,
"submitter": "Jonathan Quirola at Radboud University <jaquirola1990@gmail.com>",
"circularId": 41557,
"submittedHow": "web"
},
"message_text": "\nA. J. Levan (Radboud and Warwick), J. A. Quirola-Vasquez (Radboud), P. G. Jonker (Radboud), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), R. A. J. Eyles-Ferris (Leicester), A. Martin-Carrillo (UCD), report on behalf of a larger collaboration:\n\nWe observed the location of the optical counterpart (Levan et al., GCN 41554) to EP250827a (Hua et al., GCN 41553) with Gemini-South and the GMOS instrument using the B480 grating and a 1 arcsec slit. Four 300 s exposures were obtained. Observations began on 2025 Aug 27 at 08:51 UT, approximately 71 min after the EP trigger time. The data was reduced using DRAGONS.\n\nSeveral metallic absorption lines (due to e.g. Fe II and Mg II) at a redshift of z = 1.613 are present, suggesting the FXT lies at this redshift or beyond.\n\nWe thank the staff of Gemini, especially K. Silva, for their outstanding work in rapidly obtaining these observations. \n",
"published": "2025-09-08T08:09:03.032195Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:09:03.032212Z",
"modified": "2025-09-08T08:09:03.038150Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773032,
"topic": "gcn.circulars",
"uuid": "3da6b4ec-0213-4a08-9bbf-be75e072c5a2",
"title": "EP250827a: Gemini-South redshift z = 1.613",
"submitter": "Jonathan Quirola at Radboud University <jaquirola1990@gmail.com>",
"authors": "Jonathan Quirola at Radboud University <jaquirola1990@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41557"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: Gemini-South redshift z = 1.613",
"createdOn": 1756286655467,
"submitter": "Jonathan Quirola at Radboud University <jaquirola1990@gmail.com>",
"circularId": 41557,
"submittedHow": "web"
},
"message_text": "\nA. J. Levan (Radboud and Warwick), J. A. Quirola-Vasquez (Radboud), P. G. Jonker (Radboud), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), R. A. J. Eyles-Ferris (Leicester), A. Martin-Carrillo (UCD), report on behalf of a larger collaboration:\n\nWe observed the location of the optical counterpart (Levan et al., GCN 41554) to EP250827a (Hua et al., GCN 41553) with Gemini-South and the GMOS instrument using the B480 grating and a 1 arcsec slit. Four 300 s exposures were obtained. Observations began on 2025 Aug 27 at 08:51 UT, approximately 71 min after the EP trigger time. The data was reduced using DRAGONS.\n\nSeveral metallic absorption lines (due to e.g. Fe II and Mg II) at a redshift of z = 1.613 are present, suggesting the FXT lies at this redshift or beyond.\n\nWe thank the staff of Gemini, especially K. Silva, for their outstanding work in rapidly obtaining these observations. \n",
"published": "2025-08-27T09:24:24.411355Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T09:24:24.411378Z",
"modified": "2025-08-27T09:24:24.421136Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773030,
"topic": "gcn.circulars",
"uuid": "66f4c4ad-98a8-458f-95fb-f00206600c6c",
"title": "EP250827a: Global MASTER-Net observations report",
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"authors": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41556"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: Global MASTER-Net observations report",
"createdOn": 1756286301298,
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"circularId": 41556,
"submittedHow": "email"
},
"message_text": "V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, \nG.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),\nO.Gress, N.Budnev (ISU),\nC.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),\nA. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),\nA.Sosnovskij (CrAO),\nA. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),\nD.Buckley (SAAO),\nR.Rebolo (The Instituto de Astrofisica de Canarias),\nL.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,\nA.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) \n\nMASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250827a ( EP Team et al., GCN 41553) errorbox 371 sec after trigger time at 2025-08-27 07:46:54 UT, with upper limit up to 21.0 mag. The observations began at zenith distance = 29 deg. The sun altitude is -41.2 deg. \n\nThe galactic latitude b = -60 deg., longitude l = 313 deg.\n\n\nReal time updated cover map and OT discovered available here: \nhttps://master.sai.msu.ru/site/master2/observ.php?id=2978010\n\nWe obtain a following upper limits. \n\nTmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment\n_________|_____________________|_____________________|____________________________________|_____|_______|_______|________\n\n 407 | 2025-08-27 07:46:54 | MASTER-OAFA | (00h 13m 54.06s , -56d 38m 35.7s) | C | 70 | 20.5 | \n 492 | 2025-08-27 07:48:10 | MASTER-OAFA | (00h 13m 54.34s , -56d 38m 33.9s) | C | 90 | 20.7 | \n 599 | 2025-08-27 07:49:46 | MASTER-OAFA | (00h 13m 54.64s , -56d 38m 32.6s) | C | 110 | 20.8 | \n 680 | 2025-08-27 07:51:43 | MASTER-OAFA | (00h 13m 54.87s , -56d 38m 31.2s) | C | 40 | 20.2 | \n 726 | 2025-08-27 07:52:29 | MASTER-OAFA | (00h 13m 55.02s , -56d 38m 30.5s) | C | 40 | 20.2 | \n 772 | 2025-08-27 07:53:14 | MASTER-OAFA | (00h 13m 55.19s , -56d 38m 29.9s) | C | 40 | 20.3 | \n 817 | 2025-08-27 07:54:00 | MASTER-OAFA | (00h 13m 55.31s , -56d 38m 29.1s) | C | 40 | 20.2 | \n 863 | 2025-08-27 07:54:46 | MASTER-OAFA | (00h 13m 55.44s , -56d 38m 28.5s) | C | 40 | 20.2 | \n 909 | 2025-08-27 07:55:31 | MASTER-OAFA | (00h 13m 55.59s , -56d 38m 27.9s) | C | 40 | 20.3 | \n 955 | 2025-08-27 07:56:18 | MASTER-OAFA | (00h 13m 55.72s , -56d 38m 27.0s) | C | 40 | 20.2 | \n 995 | 2025-08-27 07:56:18 | MASTER-OAFA | (00h 13m 55.72s , -56d 38m 27.0s) | C | 120 | 20.9 | Coadd \n 1001 | 2025-08-27 07:57:03 | MASTER-OAFA | (00h 13m 55.84s , -56d 38m 26.2s) | C | 40 | 20.2 | \n 1046 | 2025-08-27 07:57:49 | MASTER-OAFA | (00h 13m 55.97s , -56d 38m 25.7s) | C | 40 | 20.2 | \n 1093 | 2025-08-27 07:58:35 | MASTER-OAFA | (00h 13m 56.15s , -56d 38m 25.0s) | C | 40 | 20.2 | \n 1133 | 2025-08-27 07:58:35 | MASTER-OAFA | (00h 13m 56.15s , -56d 38m 25.0s) | C | 120 | 21.0 | Coadd \n 1138 | 2025-08-27 07:59:21 | MASTER-OAFA | (00h 13m 56.27s , -56d 38m 24.5s) | C | 40 | 20.2 | \n 1184 | 2025-08-27 08:00:06 | MASTER-OAFA | (00h 13m 56.41s , -56d 38m 23.7s) | C | 40 | 20.3 | \n 1230 | 2025-08-27 08:00:52 | MASTER-OAFA | (00h 13m 56.58s , -56d 38m 23.2s) | C | 40 | 20.2 | \n 1270 | 2025-08-27 08:00:52 | MASTER-OAFA | (00h 13m 56.57s , -56d 38m 23.2s) | C | 120 | 21.0 | Coadd \n 1276 | 2025-08-27 08:01:38 | MASTER-OAFA | (00h 13m 56.69s , -56d 38m 22.7s) | C | 40 | 20.2 | \n 1321 | 2025-08-27 08:02:24 | MASTER-OAFA | (00h 13m 56.85s , -56d 38m 21.8s) | C | 40 | 20.2 | \n 1367 | 2025-08-27 08:03:10 | MASTER-OAFA | (00h 13m 56.98s , -56d 38m 21.1s) | C | 40 | 20.2 | \n 1413 | 2025-08-27 08:03:55 | MASTER-OAFA | (00h 13m 57.14s , -56d 38m 20.5s) | C | 40 | 20.2 | \n 1458 | 2025-08-27 08:04:40 | MASTER-OAFA | (00h 13m 57.27s , -56d 38m 19.9s) | C | 40 | 20.2 | \n 1504 | 2025-08-27 08:05:26 | MASTER-OAFA | (00h 13m 57.42s , -56d 38m 19.4s) | C | 40 | 20.2 | \n 1544 | 2025-08-27 08:05:26 | MASTER-OAFA | (00h 13m 57.42s , -56d 38m 19.4s) | C | 120 | 21.0 | Coadd \n 1549 | 2025-08-27 08:06:12 | MASTER-OAFA | (00h 13m 57.57s , -56d 38m 18.6s) | C | 40 | 20.2 | \n 1595 | 2025-08-27 08:06:58 | MASTER-OAFA | (00h 13m 57.70s , -56d 38m 18.1s) | C | 40 | 20.2 | \n 1642 | 2025-08-27 08:07:44 | MASTER-OAFA | (00h 13m 57.88s , -56d 38m 17.5s) | C | 40 | 20.2 | \n 1687 | 2025-08-27 08:08:30 | MASTER-OAFA | (00h 13m 58.02s , -56d 38m 17.0s) | C | 40 | 20.1 | \n 1732 | 2025-08-27 08:09:15 | MASTER-OAFA | (00h 13m 58.16s , -56d 38m 16.4s) | C | 40 | 20.1 | \n 3986 | 2025-08-27 08:46:38 | MASTER-OAFA | (00h 14m 05.29s , -56d 37m 56.2s) | C | 60 | 19.4 | \n 4046 | 2025-08-27 08:46:38 | MASTER-OAFA | (00h 14m 05.29s , -56d 37m 56.2s) | C | 180 | 20.0 | Coadd \n 4061 | 2025-08-27 08:47:53 | MASTER-OAFA | (00h 14m 08.12s , -56d 36m 11.6s) | C | 60 | 19.3 | \n 4137 | 2025-08-27 08:49:10 | MASTER-OAFA | (00h 14m 03.64s , -56d 37m 03.5s) | C | 60 | 19.3 | \n 4215 | 2025-08-27 08:50:28 | MASTER-OAFA | (00h 14m 02.43s , -56d 36m 02.5s) | C | 60 | 19.3 | \n 4275 | 2025-08-27 08:50:28 | MASTER-OAFA | (00h 14m 02.43s , -56d 36m 02.5s) | C | 180 | 20.0 | Coadd \n 4291 | 2025-08-27 08:51:43 | MASTER-OAFA | (00h 14m 10.29s , -56d 37m 02.2s) | C | 60 | 19.4 | \n 4369 | 2025-08-27 08:53:01 | MASTER-OAFA | (00h 14m 02.79s , -56d 38m 01.6s) | C | 60 | 19.5 | \n 4447 | 2025-08-27 08:54:19 | MASTER-OAFA | (00h 14m 09.55s , -56d 37m 48.8s) | C | 60 | 19.4 | \n 4525 | 2025-08-27 08:55:37 | MASTER-OAFA | (00h 14m 07.17s , -56d 36m 15.0s) | C | 60 | 19.3 | \n 4599 | 2025-08-27 08:56:51 | MASTER-OAFA | (00h 14m 07.39s , -56d 37m 46.8s) | C | 60 | 19.3 | \n 4674 | 2025-08-27 08:58:07 | MASTER-OAFA | (00h 14m 10.80s , -56d 36m 08.9s) | C | 60 | 19.4 | \n 4750 | 2025-08-27 08:59:23 | MASTER-OAFA | (00h 14m 04.33s , -56d 36m 58.4s) | C | 60 | 19.4 | \n 4827 | 2025-08-27 09:00:39 | MASTER-OAFA | (00h 14m 05.93s , -56d 35m 57.5s) | C | 60 | 19.4 | \n 4900 | 2025-08-27 09:02:02 | MASTER-OAFA | (00h 14m 10.40s , -56d 36m 57.1s) | C | 40 | 20.2 | \n 4945 | 2025-08-27 09:02:48 | MASTER-OAFA | (00h 14m 10.58s , -56d 36m 56.9s) | C | 40 | 20.2 | \n 4991 | 2025-08-27 09:03:33 | MASTER-OAFA | (00h 14m 10.70s , -56d 36m 56.6s) | C | 40 | 20.1 | \n 5047 | 2025-08-27 09:04:30 | MASTER-OAFA | (00h 14m 04.87s , -56d 37m 56.3s) | C | 40 | 20.1 | \n 5093 | 2025-08-27 09:05:16 | MASTER-OAFA | (00h 14m 05.01s , -56d 37m 55.8s) | C | 40 | 20.1 | \n 5138 | 2025-08-27 09:06:01 | MASTER-OAFA | (00h 14m 05.17s , -56d 37m 55.6s) | C | 40 | 20.1 | \n 5193 | 2025-08-27 09:06:55 | MASTER-OAFA | (00h 14m 11.73s , -56d 37m 28.0s) | C | 40 | 20.1 | \n 5238 | 2025-08-27 09:07:41 | MASTER-OAFA | (00h 14m 11.89s , -56d 37m 27.8s) | C | 40 | 20.2 | \n 5284 | 2025-08-27 09:08:26 | MASTER-OAFA | (00h 14m 12.04s , -56d 37m 27.5s) | C | 40 | 20.2 | \n 5342 | 2025-08-27 09:09:25 | MASTER-OAFA | (00h 14m 09.80s , -56d 36m 14.9s) | C | 40 | 20.2 | \n 5388 | 2025-08-27 09:10:10 | MASTER-OAFA | (00h 14m 09.96s , -56d 36m 14.4s) | C | 40 | 20.1 | \n 5433 | 2025-08-27 09:10:56 | MASTER-OAFA | (00h 14m 10.12s , -56d 36m 14.4s) | C | 40 | 20.1 | \n 5489 | 2025-08-27 09:11:52 | MASTER-OAFA | (00h 14m 10.28s , -56d 37m 47.0s) | C | 40 | 20.1 | \n 5535 | 2025-08-27 09:12:37 | MASTER-OAFA | (00h 14m 10.41s , -56d 37m 46.7s) | C | 40 | 20.1 | \n 5580 | 2025-08-27 09:13:23 | MASTER-OAFA | (00h 14m 10.58s , -56d 37m 46.4s) | C | 40 | 20.2 | \n 5637 | 2025-08-27 09:14:19 | MASTER-OAFA | (00h 14m 12.90s , -56d 35m 55.2s) | C | 40 | 20.1 | \nFilter C is a clear (unfiltred) band. \n\n\nThe observation and reduction will continue. \nThe message may be cited.\n",
"published": "2025-08-27T09:18:28.409141Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T09:18:28.409167Z",
"modified": "2025-08-27T09:18:28.428972Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776549,
"topic": "gcn.circulars",
"uuid": "4e558f32-fed5-487b-9618-aa6b71b3f5d1",
"title": "EP250827a: Global MASTER-Net observations report",
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"authors": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41556"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41556....1L",
"eventId": "EP250827a",
"subject": "EP250827a: Global MASTER-Net observations report",
"createdOn": 1756286301298,
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"circularId": 41556,
"submittedHow": "email"
},
"message_text": "V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, \nG.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),\nO.Gress, N.Budnev (ISU),\nC.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),\nA. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),\nA.Sosnovskij (CrAO),\nA. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),\nD.Buckley (SAAO),\nR.Rebolo (The Instituto de Astrofisica de Canarias),\nL.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,\nA.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) \n\nMASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250827a ( EP Team et al., GCN 41553) errorbox 371 sec after trigger time at 2025-08-27 07:46:54 UT, with upper limit up to 21.0 mag. The observations began at zenith distance = 29 deg. The sun altitude is -41.2 deg. \n\nThe galactic latitude b = -60 deg., longitude l = 313 deg.\n\n\nReal time updated cover map and OT discovered available here: \nhttps://master.sai.msu.ru/site/master2/observ.php?id=2978010\n\nWe obtain a following upper limits. \n\nTmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment\n_________|_____________________|_____________________|____________________________________|_____|_______|_______|________\n\n 407 | 2025-08-27 07:46:54 | MASTER-OAFA | (00h 13m 54.06s , -56d 38m 35.7s) | C | 70 | 20.5 | \n 492 | 2025-08-27 07:48:10 | MASTER-OAFA | (00h 13m 54.34s , -56d 38m 33.9s) | C | 90 | 20.7 | \n 599 | 2025-08-27 07:49:46 | MASTER-OAFA | (00h 13m 54.64s , -56d 38m 32.6s) | C | 110 | 20.8 | \n 680 | 2025-08-27 07:51:43 | MASTER-OAFA | (00h 13m 54.87s , -56d 38m 31.2s) | C | 40 | 20.2 | \n 726 | 2025-08-27 07:52:29 | MASTER-OAFA | (00h 13m 55.02s , -56d 38m 30.5s) | C | 40 | 20.2 | \n 772 | 2025-08-27 07:53:14 | MASTER-OAFA | (00h 13m 55.19s , -56d 38m 29.9s) | C | 40 | 20.3 | \n 817 | 2025-08-27 07:54:00 | MASTER-OAFA | (00h 13m 55.31s , -56d 38m 29.1s) | C | 40 | 20.2 | \n 863 | 2025-08-27 07:54:46 | MASTER-OAFA | (00h 13m 55.44s , -56d 38m 28.5s) | C | 40 | 20.2 | \n 909 | 2025-08-27 07:55:31 | MASTER-OAFA | (00h 13m 55.59s , -56d 38m 27.9s) | C | 40 | 20.3 | \n 955 | 2025-08-27 07:56:18 | MASTER-OAFA | (00h 13m 55.72s , -56d 38m 27.0s) | C | 40 | 20.2 | \n 995 | 2025-08-27 07:56:18 | MASTER-OAFA | (00h 13m 55.72s , -56d 38m 27.0s) | C | 120 | 20.9 | Coadd \n 1001 | 2025-08-27 07:57:03 | MASTER-OAFA | (00h 13m 55.84s , -56d 38m 26.2s) | C | 40 | 20.2 | \n 1046 | 2025-08-27 07:57:49 | MASTER-OAFA | (00h 13m 55.97s , -56d 38m 25.7s) | C | 40 | 20.2 | \n 1093 | 2025-08-27 07:58:35 | MASTER-OAFA | (00h 13m 56.15s , -56d 38m 25.0s) | C | 40 | 20.2 | \n 1133 | 2025-08-27 07:58:35 | MASTER-OAFA | (00h 13m 56.15s , -56d 38m 25.0s) | C | 120 | 21.0 | Coadd \n 1138 | 2025-08-27 07:59:21 | MASTER-OAFA | (00h 13m 56.27s , -56d 38m 24.5s) | C | 40 | 20.2 | \n 1184 | 2025-08-27 08:00:06 | MASTER-OAFA | (00h 13m 56.41s , -56d 38m 23.7s) | C | 40 | 20.3 | \n 1230 | 2025-08-27 08:00:52 | MASTER-OAFA | (00h 13m 56.58s , -56d 38m 23.2s) | C | 40 | 20.2 | \n 1270 | 2025-08-27 08:00:52 | MASTER-OAFA | (00h 13m 56.57s , -56d 38m 23.2s) | C | 120 | 21.0 | Coadd \n 1276 | 2025-08-27 08:01:38 | MASTER-OAFA | (00h 13m 56.69s , -56d 38m 22.7s) | C | 40 | 20.2 | \n 1321 | 2025-08-27 08:02:24 | MASTER-OAFA | (00h 13m 56.85s , -56d 38m 21.8s) | C | 40 | 20.2 | \n 1367 | 2025-08-27 08:03:10 | MASTER-OAFA | (00h 13m 56.98s , -56d 38m 21.1s) | C | 40 | 20.2 | \n 1413 | 2025-08-27 08:03:55 | MASTER-OAFA | (00h 13m 57.14s , -56d 38m 20.5s) | C | 40 | 20.2 | \n 1458 | 2025-08-27 08:04:40 | MASTER-OAFA | (00h 13m 57.27s , -56d 38m 19.9s) | C | 40 | 20.2 | \n 1504 | 2025-08-27 08:05:26 | MASTER-OAFA | (00h 13m 57.42s , -56d 38m 19.4s) | C | 40 | 20.2 | \n 1544 | 2025-08-27 08:05:26 | MASTER-OAFA | (00h 13m 57.42s , -56d 38m 19.4s) | C | 120 | 21.0 | Coadd \n 1549 | 2025-08-27 08:06:12 | MASTER-OAFA | (00h 13m 57.57s , -56d 38m 18.6s) | C | 40 | 20.2 | \n 1595 | 2025-08-27 08:06:58 | MASTER-OAFA | (00h 13m 57.70s , -56d 38m 18.1s) | C | 40 | 20.2 | \n 1642 | 2025-08-27 08:07:44 | MASTER-OAFA | (00h 13m 57.88s , -56d 38m 17.5s) | C | 40 | 20.2 | \n 1687 | 2025-08-27 08:08:30 | MASTER-OAFA | (00h 13m 58.02s , -56d 38m 17.0s) | C | 40 | 20.1 | \n 1732 | 2025-08-27 08:09:15 | MASTER-OAFA | (00h 13m 58.16s , -56d 38m 16.4s) | C | 40 | 20.1 | \n 3986 | 2025-08-27 08:46:38 | MASTER-OAFA | (00h 14m 05.29s , -56d 37m 56.2s) | C | 60 | 19.4 | \n 4046 | 2025-08-27 08:46:38 | MASTER-OAFA | (00h 14m 05.29s , -56d 37m 56.2s) | C | 180 | 20.0 | Coadd \n 4061 | 2025-08-27 08:47:53 | MASTER-OAFA | (00h 14m 08.12s , -56d 36m 11.6s) | C | 60 | 19.3 | \n 4137 | 2025-08-27 08:49:10 | MASTER-OAFA | (00h 14m 03.64s , -56d 37m 03.5s) | C | 60 | 19.3 | \n 4215 | 2025-08-27 08:50:28 | MASTER-OAFA | (00h 14m 02.43s , -56d 36m 02.5s) | C | 60 | 19.3 | \n 4275 | 2025-08-27 08:50:28 | MASTER-OAFA | (00h 14m 02.43s , -56d 36m 02.5s) | C | 180 | 20.0 | Coadd \n 4291 | 2025-08-27 08:51:43 | MASTER-OAFA | (00h 14m 10.29s , -56d 37m 02.2s) | C | 60 | 19.4 | \n 4369 | 2025-08-27 08:53:01 | MASTER-OAFA | (00h 14m 02.79s , -56d 38m 01.6s) | C | 60 | 19.5 | \n 4447 | 2025-08-27 08:54:19 | MASTER-OAFA | (00h 14m 09.55s , -56d 37m 48.8s) | C | 60 | 19.4 | \n 4525 | 2025-08-27 08:55:37 | MASTER-OAFA | (00h 14m 07.17s , -56d 36m 15.0s) | C | 60 | 19.3 | \n 4599 | 2025-08-27 08:56:51 | MASTER-OAFA | (00h 14m 07.39s , -56d 37m 46.8s) | C | 60 | 19.3 | \n 4674 | 2025-08-27 08:58:07 | MASTER-OAFA | (00h 14m 10.80s , -56d 36m 08.9s) | C | 60 | 19.4 | \n 4750 | 2025-08-27 08:59:23 | MASTER-OAFA | (00h 14m 04.33s , -56d 36m 58.4s) | C | 60 | 19.4 | \n 4827 | 2025-08-27 09:00:39 | MASTER-OAFA | (00h 14m 05.93s , -56d 35m 57.5s) | C | 60 | 19.4 | \n 4900 | 2025-08-27 09:02:02 | MASTER-OAFA | (00h 14m 10.40s , -56d 36m 57.1s) | C | 40 | 20.2 | \n 4945 | 2025-08-27 09:02:48 | MASTER-OAFA | (00h 14m 10.58s , -56d 36m 56.9s) | C | 40 | 20.2 | \n 4991 | 2025-08-27 09:03:33 | MASTER-OAFA | (00h 14m 10.70s , -56d 36m 56.6s) | C | 40 | 20.1 | \n 5047 | 2025-08-27 09:04:30 | MASTER-OAFA | (00h 14m 04.87s , -56d 37m 56.3s) | C | 40 | 20.1 | \n 5093 | 2025-08-27 09:05:16 | MASTER-OAFA | (00h 14m 05.01s , -56d 37m 55.8s) | C | 40 | 20.1 | \n 5138 | 2025-08-27 09:06:01 | MASTER-OAFA | (00h 14m 05.17s , -56d 37m 55.6s) | C | 40 | 20.1 | \n 5193 | 2025-08-27 09:06:55 | MASTER-OAFA | (00h 14m 11.73s , -56d 37m 28.0s) | C | 40 | 20.1 | \n 5238 | 2025-08-27 09:07:41 | MASTER-OAFA | (00h 14m 11.89s , -56d 37m 27.8s) | C | 40 | 20.2 | \n 5284 | 2025-08-27 09:08:26 | MASTER-OAFA | (00h 14m 12.04s , -56d 37m 27.5s) | C | 40 | 20.2 | \n 5342 | 2025-08-27 09:09:25 | MASTER-OAFA | (00h 14m 09.80s , -56d 36m 14.9s) | C | 40 | 20.2 | \n 5388 | 2025-08-27 09:10:10 | MASTER-OAFA | (00h 14m 09.96s , -56d 36m 14.4s) | C | 40 | 20.1 | \n 5433 | 2025-08-27 09:10:56 | MASTER-OAFA | (00h 14m 10.12s , -56d 36m 14.4s) | C | 40 | 20.1 | \n 5489 | 2025-08-27 09:11:52 | MASTER-OAFA | (00h 14m 10.28s , -56d 37m 47.0s) | C | 40 | 20.1 | \n 5535 | 2025-08-27 09:12:37 | MASTER-OAFA | (00h 14m 10.41s , -56d 37m 46.7s) | C | 40 | 20.1 | \n 5580 | 2025-08-27 09:13:23 | MASTER-OAFA | (00h 14m 10.58s , -56d 37m 46.4s) | C | 40 | 20.2 | \n 5637 | 2025-08-27 09:14:19 | MASTER-OAFA | (00h 14m 12.90s , -56d 35m 55.2s) | C | 40 | 20.1 | \nFilter C is a clear (unfiltred) band. \n\n\nThe observation and reduction will continue. \nThe message may be cited.\n",
"published": "2025-09-08T08:08:41.133344Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:41.133362Z",
"modified": "2025-09-08T08:08:41.138753Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776720,
"topic": "gcn.circulars",
"uuid": "6f162c8c-8e9a-453a-998b-6a1ced979b43",
"title": "EP250827a: GOTO observation of the optical afterglow",
"submitter": "d.s.oneill@bham.ac.uk",
"authors": "d.s.oneill@bham.ac.uk",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41567"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41567....1O",
"eventId": "EP250827a",
"subject": "EP250827a: GOTO observation of the optical afterglow",
"createdOn": 1756313519115,
"submitter": "d.s.oneill@bham.ac.uk",
"circularId": 41567,
"submittedHow": "web"
},
"message_text": "D. O'Neill, B. P. Gompertz, G. Ramsay, A. Kumar, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares\n\nReport on behalf of the GOTO collaboration:\n\nWe report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the EP250827a (Hua et al. GCN 41553). Targeted observations were taken at 2025-08-27 15:50:54 UT (+8.17h post trigger). The observations consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. \n\nWe detect the optical counterpart (Levan et al., GCNs 41554, 41557; Li et al., GCN 41555; Lipunov et al., GCN 41558; Gritsevich et al., GCN 41559, An et al., GCN 41660, Ghosh et al. GCN 41564) at L = 18.63 ± 0.04 AB mag.\nWe find no evidence of the source prior to the GRB trigger time in previous GOTO observations taken at 2025-08-25 12:46:35 UT down to a 5-sigma limit L>19.42 AB mag. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and not corrected for Galactic extinction.\n\nGOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).\n",
"published": "2025-09-08T08:08:49.586993Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:49.587007Z",
"modified": "2025-09-08T08:08:49.591191Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773123,
"topic": "gcn.circulars",
"uuid": "da2a97db-1881-43e7-96ca-72b8559fd45d",
"title": "EP250827a: GOTO observation of the optical afterglow",
"submitter": "d.s.oneill@bham.ac.uk",
"authors": "d.s.oneill@bham.ac.uk",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41567"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: GOTO observation of the optical afterglow",
"createdOn": 1756313519115,
"submitter": "d.s.oneill@bham.ac.uk",
"circularId": 41567,
"submittedHow": "web"
},
"message_text": "D. O'Neill, B. P. Gompertz, G. Ramsay, A. Kumar, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares\n\nReport on behalf of the GOTO collaboration:\n\nWe report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the EP250827a (Hua et al. GCN 41553). Targeted observations were taken at 2025-08-27 15:50:54 UT (+8.17h post trigger). The observations consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. \n\nWe detect the optical counterpart (Levan et al., GCNs 41554, 41557; Li et al., GCN 41555; Lipunov et al., GCN 41558; Gritsevich et al., GCN 41559, An et al., GCN 41660, Ghosh et al. GCN 41564) at L = 18.63 ± 0.04 AB mag.\nWe find no evidence of the source prior to the GRB trigger time in previous GOTO observations taken at 2025-08-25 12:46:35 UT down to a 5-sigma limit L>19.42 AB mag. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and not corrected for Galactic extinction.\n\nGOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).\n",
"published": "2025-08-27T16:52:07.555851Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T16:52:07.555868Z",
"modified": "2025-08-27T16:52:07.565507Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773043,
"topic": "gcn.circulars",
"uuid": "6b76faae-a891-4f86-a75d-eb8bf70da819",
"title": "EP250827a / GRB 250725A: MASTER-OAFA OT observation",
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"authors": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41558"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a / GRB 250725A: MASTER-OAFA OT observation",
"createdOn": 1756289382997,
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"circularId": 41558,
"submittedHow": "email"
},
"message_text": "V.Lipunov, A.Kuznetsov, I.Panchenko, G.Antipov, P.Balanutsa, K.Zhirkov (Lomonosov MSU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (OAFA),\nA.Chasovnikov, E.Gorbovskoy, N.Tiurina, Ya.Kechin, D.Vlasenko, V.Senik, M. Shilova, I.Lipunov, V.Topolev (Lomonosov MSU), O.Gress, N.Budnev(ISU),\nD.Buckley (SAAO),\nA.Sosnovskij (Crao RAS),\nA. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),\nR.Rebolo (The Instituto de Astrofisica de Canarias),\nL.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro AstrophysicsObservatory\nA. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)\n\nMASTER-OAFA robotic telescope (Lipunov et al. GCN 41556)\nstarted EP GRB 250827A observation at 2025-08-27 07:46:54 UT\nand detected optical couterpart of this GRB\nMASTER OT J001352.27-562952.8 with m_OT (unfiltered) = 18.9m (preliminary) at 2025-08-27 07:48:10 https://master.sai.msu.ru/site/master2/event.php?id=2978010 The light curve demonstrates multipeak structure from 18 to 19 during last hour.\n\nThis OT coincide with GEMINI-South detection ( GCN 41554 Levan et al.) and Las Cumbres one (GCN 41555 Wenxiong Li et al.)\n",
"published": "2025-08-27T10:09:51.541166Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T10:09:51.541184Z",
"modified": "2025-08-27T10:09:51.552904Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773081,
"topic": "gcn.circulars",
"uuid": "02a134ca-8e91-48e0-aef2-9ff41cf82bb1",
"title": "EP250827a / GRB 250827A: MASTER-OAFA OT observation",
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"authors": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41558"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a / GRB 250827A: MASTER-OAFA OT observation",
"version": 2,
"editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Vladimir Lipunov at Lomonosov Moscow State University <lipunov@sai.msu.ru>",
"editedOn": 1756300847523,
"createdOn": 1756289382997,
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"circularId": 41558,
"submittedHow": "email"
},
"message_text": "V.Lipunov, A.Kuznetsov, I.Panchenko, G.Antipov, P.Balanutsa, K.Zhirkov (Lomonosov MSU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (OAFA),\nA.Chasovnikov, E.Gorbovskoy, N.Tiurina, Ya.Kechin, D.Vlasenko, V.Senik, M. Shilova, I.Lipunov, V.Topolev (Lomonosov MSU), O.Gress, N.Budnev(ISU),\nD.Buckley (SAAO),\nA.Sosnovskij (Crao RAS),\nA. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),\nR.Rebolo (The Instituto de Astrofisica de Canarias),\nL.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro AstrophysicsObservatory\nA. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)\n\nMASTER-OAFA robotic telescope (Lipunov et al. GCN 41556)\nstarted EP GRB 250827A observation at 2025-08-27 07:46:54 UT\nand detected optical couterpart of this GRB\nMASTER OT J001352.27-562952.8 with m_OT (unfiltered) = 18.9m (preliminary) at 2025-08-27 07:48:10 https://master.sai.msu.ru/site/master2/event.php?id=2978010 The light curve demonstrates multipeak structure from 18 to 19 during last hour.\n\nThis OT coincide with GEMINI-South detection ( GCN 41554 Levan et al.) and Las Cumbres one (GCN 41555 Wenxiong Li et al.)\n",
"published": "2025-08-27T13:20:51.966981Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T13:20:51.967001Z",
"modified": "2025-08-27T13:20:51.978848Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776638,
"topic": "gcn.circulars",
"uuid": "abbb7c2a-1c4a-427d-820f-360d78868e9d",
"title": "EP250827a / GRB 250827A: MASTER-OAFA OT observation",
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"authors": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41558"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41558....1L",
"eventId": "EP250827a",
"subject": "EP250827a / GRB 250827A: MASTER-OAFA OT observation",
"version": 2,
"editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Vladimir Lipunov at Lomonosov Moscow State University <lipunov@sai.msu.ru>",
"editedOn": 1756300847523,
"createdOn": 1756289382997,
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"circularId": 41558,
"submittedHow": "email"
},
"message_text": "V.Lipunov, A.Kuznetsov, I.Panchenko, G.Antipov, P.Balanutsa, K.Zhirkov (Lomonosov MSU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (OAFA),\nA.Chasovnikov, E.Gorbovskoy, N.Tiurina, Ya.Kechin, D.Vlasenko, V.Senik, M. Shilova, I.Lipunov, V.Topolev (Lomonosov MSU), O.Gress, N.Budnev(ISU),\nD.Buckley (SAAO),\nA.Sosnovskij (Crao RAS),\nA. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),\nR.Rebolo (The Instituto de Astrofisica de Canarias),\nL.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro AstrophysicsObservatory\nA. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)\n\nMASTER-OAFA robotic telescope (Lipunov et al. GCN 41556)\nstarted EP GRB 250827A observation at 2025-08-27 07:46:54 UT\nand detected optical couterpart of this GRB\nMASTER OT J001352.27-562952.8 with m_OT (unfiltered) = 18.9m (preliminary) at 2025-08-27 07:48:10 https://master.sai.msu.ru/site/master2/event.php?id=2978010 The light curve demonstrates multipeak structure from 18 to 19 during last hour.\n\nThis OT coincide with GEMINI-South detection ( GCN 41554 Levan et al.) and Las Cumbres one (GCN 41555 Wenxiong Li et al.)\n",
"published": "2025-09-08T08:08:46.502773Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:46.502787Z",
"modified": "2025-09-08T08:08:46.507340Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5782301,
"topic": "gcn.circulars",
"uuid": "108939d0-8aee-4f2a-9b49-dad471511d1f",
"title": "EP250827a: Las Cumbres independent detection of the optical counterpart",
"submitter": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"authors": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41555"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41555....1L",
"eventId": "EP250827a",
"subject": "EP250827a: Las Cumbres independent detection of the optical counterpart",
"version": 2,
"editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"editedOn": 1758894653823,
"createdOn": 1756285364292,
"submitter": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"circularId": 41555,
"submittedHow": "web"
},
"message_text": "\nWenxiong Li (NAOC), Ido Keinan (TAU), Iair Arcavi (TAU), David Sand (U of Arizona)\n\nWe observed the position of EP250827a (Hua et al. GCN 41553) with a Las Cumbres 1m telescope at CTIO starting on 2025-08-27 07:51:31 UT (less than 5 minutes after the alert and less than 11 minutes after the event). We obtained 2x300s exposures in the broad optical w band.\n\nWe find a source at RA=3.4679 Dec=-56.4979, not present in archival Legacy Survey (https://www.legacysurvey.org/viewer) images and measure a magnitude of 18.71 +- 0.06, calibrated to the r band (consistent with the Gemini detection; Levan et al. GCN 41554).\n\nAddition followup is encouraged.",
"published": "2025-09-26T13:50:57.977914Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-26T13:50:57.977934Z",
"modified": "2025-09-26T13:50:57.988545Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773027,
"topic": "gcn.circulars",
"uuid": "46b84ddc-947a-4dae-8f54-41aa47ae5da9",
"title": "EP250827a: Las Cumbres independent detection of the optical counterpart",
"submitter": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"authors": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41555"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: Las Cumbres independent detection of the optical counterpart",
"createdOn": 1756285364292,
"submitter": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"circularId": 41555,
"submittedHow": "web"
},
"message_text": "\nWenxiong Li (NAOC), Ido Keinan (TAU), Iair Arcavi (TAU), David Sand (U of Arizona)\n\nWe observed the position of EP250827a (Hua et al. GCN 41553) with a Las Cumbres 1m telescope at CTIO starting on 2025-08-27 07:51:31 UT (less than 5 minutes after the alert and less than 11 minutes after the event). We obtained 2x300s exposures in the broad optical w band.\n\nWe find a source at RA=3.4679 Dec=56.4979, not present in archival Legacy Survey (https://www.legacysurvey.org/viewer) images and measure a magnitude of 18.71 +- 0.06, calibrated to the r band (consistent with the Gemini detection; Levan et al. GCN 41554).\n\nAddition followup is encouraged.",
"published": "2025-08-27T09:02:53.533996Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T09:02:53.534014Z",
"modified": "2025-08-27T09:02:53.542369Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776818,
"topic": "gcn.circulars",
"uuid": "0fb13fae-59ed-4b59-bfca-4b56ae70ba97",
"title": "EP250827a: Las Cumbres independent detection of the optical counterpart",
"submitter": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"authors": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41555"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41555....1L",
"eventId": "EP250827a",
"subject": "EP250827a: Las Cumbres independent detection of the optical counterpart",
"createdOn": 1756285364292,
"submitter": "Wenxiong Li at NAOC <liwenxiong1992@gmail.com>",
"circularId": 41555,
"submittedHow": "web"
},
"message_text": "\nWenxiong Li (NAOC), Ido Keinan (TAU), Iair Arcavi (TAU), David Sand (U of Arizona)\n\nWe observed the position of EP250827a (Hua et al. GCN 41553) with a Las Cumbres 1m telescope at CTIO starting on 2025-08-27 07:51:31 UT (less than 5 minutes after the alert and less than 11 minutes after the event). We obtained 2x300s exposures in the broad optical w band.\n\nWe find a source at RA=3.4679 Dec=56.4979, not present in archival Legacy Survey (https://www.legacysurvey.org/viewer) images and measure a magnitude of 18.71 +- 0.06, calibrated to the r band (consistent with the Gemini detection; Levan et al. GCN 41554).\n\nAddition followup is encouraged.",
"published": "2025-09-08T08:09:02.948852Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:09:02.948870Z",
"modified": "2025-09-08T08:09:02.952725Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776723,
"topic": "gcn.circulars",
"uuid": "7526858c-fe29-4284-85be-384419f01cb6",
"title": "EP250827a: LCO observations show fading optical counterpart",
"submitter": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"authors": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41576"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41576....1E",
"eventId": "EP250827a",
"subject": "EP250827a: LCO observations show fading optical counterpart",
"createdOn": 1756390731696,
"submitter": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"circularId": 41576,
"submittedHow": "web"
},
"message_text": "R. A. J. Eyles-Ferris (Leicester), J. A. Quirola-Vasquez (Radboud), A. J. Levan (Radboud and Warwick), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), F. E. Bauer (SSI and UTA), and J. Chacón (PUC) report on behalf of a larger collaboration:\n\nWe observed the location of the optical counterpart (Levan et al., GCN 41554; Li et al., GCN 41555; Levan et al., GCN 41557; Lipunov et al., GCN 41558; Gritsevich et al., GCN 41559; An et al., GCN 41560; Ghosh et al., GCN 41564; O’Neill et al., GCN 41567; Pérez-Fournon et al., GCN 41568; Passaleva et al., GCN 41570) to EP250827a (Hua et al., GCN 41553; Ni et al., GCN 41573) with the Sinistro instruments mounted on 1-m telescopes at the LCO SAAO and Cerro Tololo Inter-American Observatory nodes. 5x300 s exposures were obtained in each of the SDSS u, g and r filters with start times from 2025 Aug 27 at 22:38:04 to 2025 Aug 28 04:36:48 UT.\n\nThe counterpart is clearly detected in both the g and r filters and is marginally detected in the u filter image. At 15.0 hr after the EP trigger, we measure r = 19.99 +/- 0.05, ~1.5 mags fainter than observed by Ghosh et al. (GCN 41564). Assuming an unbroken power-law decay between the two epochs, we derive a temporal index alpha ~ 1.4 for the decay.",
"published": "2025-09-08T08:08:49.629545Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:49.629563Z",
"modified": "2025-09-08T08:08:49.633559Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773382,
"topic": "gcn.circulars",
"uuid": "849404db-8651-40fe-b2bf-04a45ae1d4a8",
"title": "EP250827a: LCO observations show fading optical counterpart",
"submitter": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"authors": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41576"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: LCO observations show fading optical counterpart",
"createdOn": 1756390731696,
"submitter": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"circularId": 41576,
"submittedHow": "web"
},
"message_text": "R. A. J. Eyles-Ferris (Leicester), J. A. Quirola-Vasquez (Radboud), A. J. Levan (Radboud and Warwick), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), F. E. Bauer (SSI and UTA), and J. Chacón (PUC) report on behalf of a larger collaboration:\n\nWe observed the location of the optical counterpart (Levan et al., GCN 41554; Li et al., GCN 41555; Levan et al., GCN 41557; Lipunov et al., GCN 41558; Gritsevich et al., GCN 41559; An et al., GCN 41560; Ghosh et al., GCN 41564; O’Neill et al., GCN 41567; Pérez-Fournon et al., GCN 41568; Passaleva et al., GCN 41570) to EP250827a (Hua et al., GCN 41553; Ni et al., GCN 41573) with the Sinistro instruments mounted on 1-m telescopes at the LCO SAAO and Cerro Tololo Inter-American Observatory nodes. 5x300 s exposures were obtained in each of the SDSS u, g and r filters with start times from 2025 Aug 27 at 22:38:04 to 2025 Aug 28 04:36:48 UT.\n\nThe counterpart is clearly detected in both the g and r filters and is marginally detected in the u filter image. At 15.0 hr after the EP trigger, we measure r = 19.99 +/- 0.05, ~1.5 mags fainter than observed by Ghosh et al. (GCN 41564). Assuming an unbroken power-law decay between the two epochs, we derive a temporal index alpha ~ 1.4 for the decay.",
"published": "2025-08-28T14:19:02.291760Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-28T14:19:02.291779Z",
"modified": "2025-08-28T14:19:02.309984Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776640,
"topic": "gcn.circulars",
"uuid": "7fb90830-9a81-404d-b3b0-2dbf5061cd6a",
"title": "EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations",
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"authors": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41573"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41573....1N",
"eventId": "EP250827a",
"subject": "EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations",
"createdOn": 1756369252156,
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"circularId": 41573,
"submittedHow": "web"
},
"message_text": "K. R. Ni (CCNU), Y. L. Hua (PMO,CAS), M. J. Liu and C. C. Jin (NAO,CAS) on behalf of the Einstein Probe (EP) team: \n\nThe X-ray transient EP250827a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hua et al., GCN 41553). We report on the refined analysis of WXT and FXT observations. The WXT data shows that the event started at T0=2025-08-27T07:39:01 (UTC) and lasted for at least 90 s. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.19 x 10^20 cm^-2 and a photon index of 0.73 (-0.47/+0.50). The derived average unabsorbed 0.5-4 keV flux is 1.71(-0.34/+0.42) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.\n \nThe Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 102 s after T0. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 3.46915, DEC = -56.4998 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), within the WXT error circle. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.19 x 10^20 cm^-2 and a photon index of 2.0(-0.10/+0.10). The derived average unabsorbed 0.5-10 keV flux is 4.38 (-0.38/+0.39) x 10^(-12)erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. \n \nLaunched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).",
"published": "2025-09-08T08:08:46.526016Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:46.526031Z",
"modified": "2025-09-08T08:08:46.530363Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773314,
"topic": "gcn.circulars",
"uuid": "d40767ac-241b-43ff-b5ac-2fbc21f9c0a1",
"title": "EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations",
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"authors": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41573"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations",
"createdOn": 1756369252156,
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"circularId": 41573,
"submittedHow": "web"
},
"message_text": "K. R. Ni (CCNU), Y. L. Hua (PMO,CAS), M. J. Liu and C. C. Jin (NAO,CAS) on behalf of the Einstein Probe (EP) team: \n\nThe X-ray transient EP250827a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hua et al., GCN 41553). We report on the refined analysis of WXT and FXT observations. The WXT data shows that the event started at T0=2025-08-27T07:39:01 (UTC) and lasted for at least 90 s. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.19 x 10^20 cm^-2 and a photon index of 0.73 (-0.47/+0.50). The derived average unabsorbed 0.5-4 keV flux is 1.71(-0.34/+0.42) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.\n \nThe Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 102 s after T0. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 3.46915, DEC = -56.4998 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), within the WXT error circle. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.19 x 10^20 cm^-2 and a photon index of 2.0(-0.10/+0.10). The derived average unabsorbed 0.5-10 keV flux is 4.38 (-0.38/+0.39) x 10^(-12)erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. \n \nLaunched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).",
"published": "2025-08-28T08:21:01.008328Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-28T08:21:01.008343Z",
"modified": "2025-08-28T08:21:01.011295Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776827,
"topic": "gcn.circulars",
"uuid": "cda3634e-90cb-4995-a343-0f0bb0b5b465",
"title": "EP250827a: STEP/T80S Confirmation of fading optical counterpart ",
"submitter": "André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos@gmail.com>",
"authors": "André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41580"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41580....1S",
"eventId": "EP250827a",
"subject": "EP250827a: STEP/T80S Confirmation of fading optical counterpart ",
"createdOn": 1756409677477,
"submitter": "André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos@gmail.com>",
"circularId": 41580,
"submittedHow": "web"
},
"message_text": "A. Santos (CBPF), C. R. Bom (CBPF), C. D. Kilpatrick (Northwestern), L. Santana-Silva (CBPF), P. Darc (CBPF), Gabriel Teixeira (CBPF), C. Mendes de Oliveira (IAG-USP) report on behalf of the STEP collaboration:\n\nWe conducted optical follow up with the T80S 0.8-m robotic telescope as part of the S-PLUS Transient Extension Program (Santos et al., 2024, MNRAS, 529, 59) targeting the fast X-ray transient EP250827a by the Einstein Probe instrument (GCN 41533). The T80S observations started on Aug 28 06:34:09 UT (~23 hours after the trigger). We obtained imaging with exposure time 2x120s r-band and 2x150s in i-band with the T80S camera centered at the position of the optical afterglow detection reported in Levan et al., (GCN 41554); Li et al., GCN (41555); Levan et al., (GCN 41557); Lipunov et al., (GCN 41558); Gritsevich et al., (GCN 41559); An et al., (GCN 41560); Ghosh et al., GCN (41564); O’Neill et al., (GCN 41567); Pérez-Fournon et al., (GCN 41568); Passaleva et al., (GCN 41570) to EP250827a Hua et al., (GCN 41553); Ni et al., (GCN 41573) and Eyles-Ferris et al. (GCN 41576).\n\nSubtracting DECam template images from the T80S stacked frames using photpipe (Rest et al., 2005, ApJ, 634, 1103), we detect the afterglow at the previously reported position.\n\nMEAN-MJD FILTER Magnitude Uncertainty Limit (3sigma)\n60915.2823 r 21.32 0.12 22.86\n60915.2778 i 20.98 0.16 22.39\n\nThe counterpart is detected both in r and i bands. Given the time of imaging at 23.0 hr after the EP trigger and the measured magnitude, we argued the optical counterparting is fading after the rebrightening reported by Ghosh et al. (GCN 41564), confirming the fading reported by Eyles-Ferris (GCN 41576). \n\nWe acknowledge the T80S technical team with the provided support during the night.",
"published": "2025-09-08T08:09:03.067379Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:09:03.067395Z",
"modified": "2025-09-08T08:09:03.071479Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773437,
"topic": "gcn.circulars",
"uuid": "2a20ced4-9973-40cc-8bce-ab0f1e3d51ff",
"title": "EP250827a: STEP/T80S Confirmation of fading optical counterpart ",
"submitter": "André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos@gmail.com>",
"authors": "André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41580"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: STEP/T80S Confirmation of fading optical counterpart ",
"createdOn": 1756409677477,
"submitter": "André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos@gmail.com>",
"circularId": 41580,
"submittedHow": "web"
},
"message_text": "A. Santos (CBPF), C. R. Bom (CBPF), C. D. Kilpatrick (Northwestern), L. Santana-Silva (CBPF), P. Darc (CBPF), Gabriel Teixeira (CBPF), C. Mendes de Oliveira (IAG-USP) report on behalf of the STEP collaboration:\n\nWe conducted optical follow up with the T80S 0.8-m robotic telescope as part of the S-PLUS Transient Extension Program (Santos et al., 2024, MNRAS, 529, 59) targeting the fast X-ray transient EP250827a by the Einstein Probe instrument (GCN 41533). The T80S observations started on Aug 28 06:34:09 UT (~23 hours after the trigger). We obtained imaging with exposure time 2x120s r-band and 2x150s in i-band with the T80S camera centered at the position of the optical afterglow detection reported in Levan et al., (GCN 41554); Li et al., GCN (41555); Levan et al., (GCN 41557); Lipunov et al., (GCN 41558); Gritsevich et al., (GCN 41559); An et al., (GCN 41560); Ghosh et al., GCN (41564); O’Neill et al., (GCN 41567); Pérez-Fournon et al., (GCN 41568); Passaleva et al., (GCN 41570) to EP250827a Hua et al., (GCN 41553); Ni et al., (GCN 41573) and Eyles-Ferris et al. (GCN 41576).\n\nSubtracting DECam template images from the T80S stacked frames using photpipe (Rest et al., 2005, ApJ, 634, 1103), we detect the afterglow at the previously reported position.\n\nMEAN-MJD FILTER Magnitude Uncertainty Limit (3sigma)\n60915.2823 r 21.32 0.12 22.86\n60915.2778 i 20.98 0.16 22.39\n\nThe counterpart is detected both in r and i bands. Given the time of imaging at 23.0 hr after the EP trigger and the measured magnitude, we argued the optical counterparting is fading after the rebrightening reported by Ghosh et al. (GCN 41564), confirming the fading reported by Eyles-Ferris (GCN 41576). \n\nWe acknowledge the T80S technical team with the provided support during the night.",
"published": "2025-08-28T19:34:47.534148Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-28T19:34:47.534167Z",
"modified": "2025-08-28T19:34:47.570981Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776762,
"topic": "gcn.circulars",
"uuid": "3be02f8a-ad5e-46f8-a6cc-19ca32e19be7",
"title": "EP250827a: Swift/UVOT Detection",
"submitter": "Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>",
"authors": "Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41585"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41585....1S",
"eventId": "EP250827a",
"subject": "EP250827a: Swift/UVOT Detection",
"createdOn": 1756441101049,
"submitter": "Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>",
"circularId": 41585,
"submittedHow": "web"
},
"message_text": "M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of EP250827a 3.2 ks after the EP trigger (Hua et al., GCN Circ. 41553). An uncatalogued source consistent with the XRT position (Evans et al., GCN Circ. 41563) and the optical transient (Levan et al., GCN Circ. 41554; Li et al., GCN Circ. 41555; Lipunov et al., GCN Circ. 41558; Gritsevich et al., GCN Circ. 41559; An et al., GCN Circ. 41560; Ghosh et al., GCN Circ. 41564; O'Neill et al., GCN Circ. 41567) is detected in the UVOT exposures.\n\nThe preliminary UVOT position is:\n RA (J2000) = 00:13:52.24 = 3.46767 (deg.)\n Dec (J2000) = -56:29:52.2 = -56.49784 (deg.) \nwith an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).\n\nPreliminary detections and 3-sigma upper limits using the UVOT photometric system\n(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: \n\nFilter T_start(s) T_stop(s) Exp(s) Mag\n\nu 3192 9257 1566 18.29+/-0.04\nu 54232 60071 939 19.69+/-0.19\nu 121367 127685 754 >20.36\nuvw1 53286 59775 1903 19.86+/-0.13\nuvw1 120301 127006 2040 >21.21\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.011 in the direction of the burst\n(Schlegel et al. 1998)",
"published": "2025-09-08T08:08:58.159179Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:58.159194Z",
"modified": "2025-09-08T08:08:58.163123Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773539,
"topic": "gcn.circulars",
"uuid": "eb2948fc-4e01-4fb1-8770-4b8addf1ab10",
"title": "EP250827a: Swift/UVOT Detection",
"submitter": "Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>",
"authors": "Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41585"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: Swift/UVOT Detection",
"createdOn": 1756441101049,
"submitter": "Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>",
"circularId": 41585,
"submittedHow": "web"
},
"message_text": "M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of EP250827a 3.2 ks after the EP trigger (Hua et al., GCN Circ. 41553). An uncatalogued source consistent with the XRT position (Evans et al., GCN Circ. 41563) and the optical transient (Levan et al., GCN Circ. 41554; Li et al., GCN Circ. 41555; Lipunov et al., GCN Circ. 41558; Gritsevich et al., GCN Circ. 41559; An et al., GCN Circ. 41560; Ghosh et al., GCN Circ. 41564; O'Neill et al., GCN Circ. 41567) is detected in the UVOT exposures.\n\nThe preliminary UVOT position is:\n RA (J2000) = 00:13:52.24 = 3.46767 (deg.)\n Dec (J2000) = -56:29:52.2 = -56.49784 (deg.) \nwith an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).\n\nPreliminary detections and 3-sigma upper limits using the UVOT photometric system\n(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: \n\nFilter T_start(s) T_stop(s) Exp(s) Mag\n\nu 3192 9257 1566 18.29+/-0.04\nu 54232 60071 939 19.69+/-0.19\nu 121367 127685 754 >20.36\nuvw1 53286 59775 1903 19.86+/-0.13\nuvw1 120301 127006 2040 >21.21\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.011 in the direction of the burst\n(Schlegel et al. 1998)",
"published": "2025-08-29T04:18:27.946366Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-29T04:18:27.946383Z",
"modified": "2025-08-29T04:18:27.956087Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776591,
"topic": "gcn.circulars",
"uuid": "3db658e5-b75b-4ec6-8407-89f7e04ee454",
"title": "EP250827a: Swift-XRT counterpart detection",
"submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"authors": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41563"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41563....1E",
"eventId": "EP250827a",
"subject": "EP250827a: Swift-XRT counterpart detection",
"createdOn": 1756308930889,
"submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"circularId": 41563,
"submittedHow": "email"
},
"message_text": "P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA), A.P.\nBeardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.\nBurrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),\nP. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), R.A.J.\nEyles-Ferris (U. Leicester), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P.\nOsborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C.\nSalvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A.\nWilliams (PSU) report on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected\nsource EP250827a, collecting 1.6 ks of Photon Counting (PC) mode data between T0+3.1\nks and T0+9.2 ks after the trigger. A likely counterpart has been found. The details\nof this source are:\n\n Source 1 (SWIFT J001351.7-562952):\n ==================================\n RA (J2000.0): 3.4656 = 00 13 51.74\n Dec (J2000.0): -56.4979 = -56 29 52.4\n Error:\t 3.7 (arcsec, radius, 90% confidence).\n Detect flag: GOOD\n Distance:\t 2.2 arcmin from the Einstein Probe/WXT position.\n Mean rate:\t 0.161 +/- 0.011 ct s^-1\n Mean flux:\t (5.48 +/- 0.39)e-12 erg cm^-2 s^-1\n Peak rate:\t 0.253 +/- 0.057 ct s^-1\n Peak flux:\t (8.6 +/- 1.9)e-12 erg cm^-2 s^-1\n ECF:\t 3.41e-11 erg cm^-2 ct^-1\n\t\t assuming NH=1.45e+20 cm^-2, gamma=1.93\n\t\t determined from a spectral fit.\n XMM UL:\t 2.2e-12 erg cm^-2 s^-1, (0.3-10 keV)\n\t\t so the source is 3.3-sigma above this 3-sigma upper limit.\n The source may be fading, at the 1.5-sigma level.\n\nThis position is consistent with the optical counterpart previously reported (Levan\net al. GCN 41554, Li et al. GCN 41555, Lipunov et al. GCN 41558, Gritsevich et al.\nGCN 41559, An et al. GCN 41560) at a redshift of 1.613 (Levan et al. GCN 41557).\n\nAll fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with\ncatalogues and upper limits from other missions, we assumed a power-law spectrum\nwith NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.\n\nThe results of the XRT-team automatic analysis of the XRT observations, including a\nposition-specific upper limit calculator, are available at\nhttps://www.swift.ac.uk/EP/EP_FIELD00062.\n\nThis circular is an official product of the Swift-XRT team.\n\n\n",
"published": "2025-09-08T08:08:41.724963Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:41.724980Z",
"modified": "2025-09-08T08:08:41.729063Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773106,
"topic": "gcn.circulars",
"uuid": "65588f78-e71a-4bd6-a943-a4c40db3c34b",
"title": "EP250827a: Swift-XRT counterpart detection",
"submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"authors": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41563"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: Swift-XRT counterpart detection",
"createdOn": 1756308930889,
"submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"circularId": 41563,
"submittedHow": "email"
},
"message_text": "P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA), A.P.\nBeardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.\nBurrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),\nP. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), R.A.J.\nEyles-Ferris (U. Leicester), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P.\nOsborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C.\nSalvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A.\nWilliams (PSU) report on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected\nsource EP250827a, collecting 1.6 ks of Photon Counting (PC) mode data between T0+3.1\nks and T0+9.2 ks after the trigger. A likely counterpart has been found. The details\nof this source are:\n\n Source 1 (SWIFT J001351.7-562952):\n ==================================\n RA (J2000.0): 3.4656 = 00 13 51.74\n Dec (J2000.0): -56.4979 = -56 29 52.4\n Error:\t 3.7 (arcsec, radius, 90% confidence).\n Detect flag: GOOD\n Distance:\t 2.2 arcmin from the Einstein Probe/WXT position.\n Mean rate:\t 0.161 +/- 0.011 ct s^-1\n Mean flux:\t (5.48 +/- 0.39)e-12 erg cm^-2 s^-1\n Peak rate:\t 0.253 +/- 0.057 ct s^-1\n Peak flux:\t (8.6 +/- 1.9)e-12 erg cm^-2 s^-1\n ECF:\t 3.41e-11 erg cm^-2 ct^-1\n\t\t assuming NH=1.45e+20 cm^-2, gamma=1.93\n\t\t determined from a spectral fit.\n XMM UL:\t 2.2e-12 erg cm^-2 s^-1, (0.3-10 keV)\n\t\t so the source is 3.3-sigma above this 3-sigma upper limit.\n The source may be fading, at the 1.5-sigma level.\n\nThis position is consistent with the optical counterpart previously reported (Levan\net al. GCN 41554, Li et al. GCN 41555, Lipunov et al. GCN 41558, Gritsevich et al.\nGCN 41559, An et al. GCN 41560) at a redshift of 1.613 (Levan et al. GCN 41557).\n\nAll fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with\ncatalogues and upper limits from other missions, we assumed a power-law spectrum\nwith NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.\n\nThe results of the XRT-team automatic analysis of the XRT observations, including a\nposition-specific upper limit calculator, are available at\nhttps://www.swift.ac.uk/EP/EP_FIELD00062.\n\nThis circular is an official product of the Swift-XRT team.\n\n\n",
"published": "2025-08-27T15:35:38.267297Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T15:35:38.267315Z",
"modified": "2025-08-27T15:35:38.365305Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776551,
"topic": "gcn.circulars",
"uuid": "ebea3f62-a258-47ff-b692-9f0948ad78bc",
"title": "EP250827a: TRT optical observations",
"submitter": "J. An <jiean0813@foxmail.com>",
"authors": "J. An <jiean0813@foxmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41560"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41560....1A",
"eventId": "EP250827a",
"subject": "EP250827a: TRT optical observations",
"createdOn": 1756290983675,
"submitter": "J. An <jiean0813@foxmail.com>",
"circularId": 41560,
"submittedHow": "web"
},
"message_text": "J. An (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Y. Fu (HUST), L.B. He, X. Liu, Z.P. Zhu, S.Q. Jiang, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration:\n\nWe observed the field of EP250827a (Hua et al., GCN 41553), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. (CTO) Observations started at 08:19:45 UTC on 2025-08-27, i.e., ~ 39 min after the EP/WXT trigger and a series of frames in the r band were obtained. \n\nWe clearly detect the optical counterpart(Levan et al., GCN 41554; Li et al., GCN 41555; Lipunov et al., GCN 41558; Gritsevich et al., GCN 41559) in our images. Preliminary photometry shows that the source has r ~ 18.93 +/- 0.03 mag at 51.6 min post-trigger, calibrated with Legacy DR10 catalog and not corrected for Galactic extinction.",
"published": "2025-09-08T08:08:41.160528Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:41.160547Z",
"modified": "2025-09-08T08:08:41.164789Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773054,
"topic": "gcn.circulars",
"uuid": "c9e9a85a-e12a-46b8-829e-c5f87248a560",
"title": "EP250827a: TRT optical observations",
"submitter": "J. An <jiean0813@foxmail.com>",
"authors": "J. An <jiean0813@foxmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41560"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: TRT optical observations",
"createdOn": 1756290983675,
"submitter": "J. An <jiean0813@foxmail.com>",
"circularId": 41560,
"submittedHow": "web"
},
"message_text": "J. An (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Y. Fu (HUST), L.B. He, X. Liu, Z.P. Zhu, S.Q. Jiang, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration:\n\nWe observed the field of EP250827a (Hua et al., GCN 41553), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. (CTO) Observations started at 08:19:45 UTC on 2025-08-27, i.e., ~ 39 min after the EP/WXT trigger and a series of frames in the r band were obtained. \n\nWe clearly detect the optical counterpart(Levan et al., GCN 41554; Li et al., GCN 41555; Lipunov et al., GCN 41558; Gritsevich et al., GCN 41559) in our images. Preliminary photometry shows that the source has r ~ 18.93 +/- 0.03 mag at 51.6 min post-trigger, calibrated with Legacy DR10 catalog and not corrected for Galactic extinction.",
"published": "2025-08-27T10:36:32.227972Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T10:36:32.227989Z",
"modified": "2025-08-27T10:36:32.238020Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773728,
"topic": "gcn.circulars",
"uuid": "a5ed2e18-220b-4458-811b-33f462795e61",
"title": "EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger",
"submitter": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
"authors": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41596"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger",
"createdOn": 1756494668080,
"submitter": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
"circularId": 41596,
"submittedHow": "web"
},
"message_text": "I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), A. López-Oramas, and D.S. Aguado (IAC and ULL)\n\nWe report on very early ATLAS detections of the optical afterglow of EP250827a, a fast X-ray transient discovered by Einstein Probe WXT (ID: 01709200787) on 2025-08-27 07:40:43 UTC (Hua et al., GCN 41553; and Ni et al., GCN 41573), with UV-optical detections reported in Levan et al. (GCN 41554), Li et al. (GCN 41555), Levan et al. (GCN 41557), Lipunov et al. (GCN 41558), Gritsevich et al. (GCN 41559), An et al. (GCN 41560), Ghosh et al. (GCN 41564), O’Neill et al. (GCN 41567), Pérez-Fournon et al. (GCN 41568), Passaleva et al. (GCN 41570), Eyles-Ferris et al. (GCN 41576), Santos et al. (GCN 41580), and Siegel et al. (GCN 41585), spectroscopic redshift of z = 1.613-1.61 (Levan et al., GCN 41557; and Passaleva et al., GCN 41570) and Swift-XRT follow-up observations (Evans et al., GCN 41563).\n\nUsing the ATLAS forced-photometry server (Shingles et al. 2021, Transient Name Server AstroNote 2021-7), we found that there were four ATLAS observations that covered the EP250827a position on 2025-08-27, two of them before the EP trigger and two after it. As expected, the source was not detected in the ATLAS pre-trigger observations but it is well detected in the two post-trigger observations, the first of them at a start time of only about 43 sec (about 16 sec in the source rest frame) after the EP trigger. There is a flux rise between the two observations. The source is well detected in both the original (reduced) and difference (reduced - reference) ATLAS images. For the forced photometry measurements, we used the coordinates of the optical counterpart given by Levan et al. (GCN 41554) from the analysis of Gemini-South GMOS observations.\n\nIn the following, we give the ATLAS limiting magnitudes and forced-photometry magnitudes (using difference images), not corrected for Galactic extinction.\n\n\nMJD | 5-sigma limit | filter | ATLAS observation |\n60914.306552 | 20.14 | orange | 04a60914o0247o |\n60914.313502 | 20.18 | orange | 04a60914o0252o |\n \n\nMJD | mag | error | filter | ATLAS observation | \n60914.320437 | 18.707 | 0.070 | orange | 04a60914o0257o |\n60914.327372 | 18.568 | 0.065 | orange | 04a60914o0262o |\n\n\nThe reported ATLAS observations MJD times are the start times of the individual 30-sec exposures.\n\nThe first detection is likely the earliest one after the trigger of an optical afterglow of EP-discovered fast X-ray transients.\n\n\n\n",
"published": "2025-08-29T19:11:17.134146Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-29T19:11:17.134161Z",
"modified": "2025-08-29T19:11:17.144702Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5780974,
"topic": "gcn.circulars",
"uuid": "479f0060-8bde-4fc4-b40f-f16e5db1b5f0",
"title": "EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger",
"submitter": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
"authors": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41596"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41596....1P",
"eventId": "EP250827a",
"subject": "EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger",
"createdOn": 1756494668080,
"submitter": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
"circularId": 41596,
"submittedHow": "web"
},
"message_text": "I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), A. López-Oramas, and D.S. Aguado (IAC and ULL)\n\nWe report on very early ATLAS detections of the optical afterglow of EP250827a, a fast X-ray transient discovered by Einstein Probe WXT (ID: 01709200787) on 2025-08-27 07:40:43 UTC (Hua et al., GCN 41553; and Ni et al., GCN 41573), with UV-optical detections reported in Levan et al. (GCN 41554), Li et al. (GCN 41555), Levan et al. (GCN 41557), Lipunov et al. (GCN 41558), Gritsevich et al. (GCN 41559), An et al. (GCN 41560), Ghosh et al. (GCN 41564), O’Neill et al. (GCN 41567), Pérez-Fournon et al. (GCN 41568), Passaleva et al. (GCN 41570), Eyles-Ferris et al. (GCN 41576), Santos et al. (GCN 41580), and Siegel et al. (GCN 41585), spectroscopic redshift of z = 1.613-1.61 (Levan et al., GCN 41557; and Passaleva et al., GCN 41570) and Swift-XRT follow-up observations (Evans et al., GCN 41563).\n\nUsing the ATLAS forced-photometry server (Shingles et al. 2021, Transient Name Server AstroNote 2021-7), we found that there were four ATLAS observations that covered the EP250827a position on 2025-08-27, two of them before the EP trigger and two after it. As expected, the source was not detected in the ATLAS pre-trigger observations but it is well detected in the two post-trigger observations, the first of them at a start time of only about 43 sec (about 16 sec in the source rest frame) after the EP trigger. There is a flux rise between the two observations. The source is well detected in both the original (reduced) and difference (reduced - reference) ATLAS images. For the forced photometry measurements, we used the coordinates of the optical counterpart given by Levan et al. (GCN 41554) from the analysis of Gemini-South GMOS observations.\n\nIn the following, we give the ATLAS limiting magnitudes and forced-photometry magnitudes (using difference images), not corrected for Galactic extinction.\n\n\nMJD | 5-sigma limit | filter | ATLAS observation |\n60914.306552 | 20.14 | orange | 04a60914o0247o |\n60914.313502 | 20.18 | orange | 04a60914o0252o |\n \n\nMJD | mag | error | filter | ATLAS observation | \n60914.320437 | 18.707 | 0.070 | orange | 04a60914o0257o |\n60914.327372 | 18.568 | 0.065 | orange | 04a60914o0262o |\n\n\nThe reported ATLAS observations MJD times are the start times of the individual 30-sec exposures.\n\nThe first detection is likely the earliest one after the trigger of an optical afterglow of EP-discovered fast X-ray transients.\n\n\n\n",
"published": "2025-09-22T08:08:49.757567Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:49.757578Z",
"modified": "2025-09-22T08:08:49.761477Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776639,
"topic": "gcn.circulars",
"uuid": "449a2a5c-cf49-4be7-86c3-3c2b12f0114a",
"title": "EP250827A: VLT/X-shooter redshift confirmation",
"submitter": "N. Passaleva at Sapienza University of Rome <niccolo.passaleva@uniroma1.it>",
"authors": "N. Passaleva at Sapienza University of Rome <niccolo.passaleva@uniroma1.it>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41570"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41570....1P",
"eventId": "EP250827a",
"subject": "EP250827A: VLT/X-shooter redshift confirmation",
"createdOn": 1756330917004,
"submitter": "N. Passaleva at Sapienza University of Rome <niccolo.passaleva@uniroma1.it>",
"circularId": 41570,
"submittedHow": "web"
},
"message_text": "Niccolò Passaleva (U Rome), Rosa L. Becerra (U Rome) , Massine El Kabir (U Rome), Yu-Han Yang (U Rome), Eleonora Troja (U Rome) report on behalf of the ERC BHianca team:\n\nWe observed the optical counterpart of EP250827a (Hua et al., GCN 41553) reported by Levan et al. (GCN 41554) and Wenxiong et al. (GCN 41555) with the X-Shooter spectrograph on the ESO VLT UT3 (Melipal). Observations began at T+1.67 hours and obtained a total of 4x600s spectra at an average airmass of about 1.45.\n\nAt the position of the optical counterpart we detect a bright continuum. We identify absorption features (e.g. Fe II, Mg I, Mg II, C lV, Si IV, Si II, Al II, Al III) at a common redshift of z ~ 1.61 confirming the result reported by Levan et al. (GCN 41557).\n\nWe thank the staff at the VLT, for the rapid execution of these observations.",
"published": "2025-09-08T08:08:46.514805Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:46.514821Z",
"modified": "2025-09-08T08:08:46.519007Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773178,
"topic": "gcn.circulars",
"uuid": "82df30f5-1d55-49cd-ab50-f8e25f68df13",
"title": "EP250827A: VLT/X-shooter redshift confirmation",
"submitter": "N. Passaleva at Sapienza University of Rome <niccolo.passaleva@uniroma1.it>",
"authors": "N. Passaleva at Sapienza University of Rome <niccolo.passaleva@uniroma1.it>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41570"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827a",
"subject": "EP250827A: VLT/X-shooter redshift confirmation",
"createdOn": 1756330917004,
"submitter": "N. Passaleva at Sapienza University of Rome <niccolo.passaleva@uniroma1.it>",
"circularId": 41570,
"submittedHow": "web"
},
"message_text": "Niccolò Passaleva (U Rome), Rosa L. Becerra (U Rome) , Massine El Kabir (U Rome), Yu-Han Yang (U Rome), Eleonora Troja (U Rome) report on behalf of the ERC BHianca team:\n\nWe observed the optical counterpart of EP250827a (Hua et al., GCN 41553) reported by Levan et al. (GCN 41554) and Wenxiong et al. (GCN 41555) with the X-Shooter spectrograph on the ESO VLT UT3 (Melipal). Observations began at T+1.67 hours and obtained a total of 4x600s spectra at an average airmass of about 1.45.\n\nAt the position of the optical counterpart we detect a bright continuum. We identify absorption features (e.g. Fe II, Mg I, Mg II, C lV, Si IV, Si II, Al II, Al III) at a common redshift of z ~ 1.61 confirming the result reported by Levan et al. (GCN 41557).\n\nWe thank the staff at the VLT, for the rapid execution of these observations.",
"published": "2025-08-27T21:42:05.715320Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-27T21:42:05.715336Z",
"modified": "2025-08-27T21:42:05.719362Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5775237,
"topic": "gcn.circulars",
"uuid": "045ddf9b-ebef-4f10-8916-ea304d929699",
"title": "EP250827b / AT 2025wkm: TRT optical observations",
"submitter": "L. B. He at NAOC <helb@bao.ac.cn>",
"authors": "L. B. He at NAOC <helb@bao.ac.cn>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41671"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827b",
"subject": "EP250827b / AT 2025wkm: TRT optical observations",
"version": 2,
"editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of L. B. He at NAOC <helb@bao.ac.cn>",
"editedOn": 1756913724610,
"createdOn": 1756911998049,
"submitter": "L. B. He at NAOC <helb@bao.ac.cn>",
"circularId": 41671,
"submittedHow": "web"
},
"message_text": "L.B. He (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Y. Fu (HUST), J. An, X. Liu, Z.P. Zhu, S.Q. Jiang, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration:\n\nWe followed up the optical transient AT 2025wkm, which is potentially associated with EP250827b (Schroeder et al., GCN 41635). Our first epoch was carried out at the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, U.S.A (SRO), approximately 5.04 days after the EP X-ray flare. And we obtained several frames in the R band.\n\nThe counterpart (Schroder et al., GCN 41635; Hall et al., GCN 41636; Hall et al., GCN 41641; Eyles-Ferris et al., GCN 41655; Ma et al., GCN 41667; Eyles-Ferris et al., GCN 41669) was clearly detected in the stacked image, with R = 19.62 +/- 0.04 (Vega), calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction.",
"published": "2025-09-03T15:35:25.027174Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-03T15:35:25.027195Z",
"modified": "2025-09-03T15:35:25.033024Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5780924,
"topic": "gcn.circulars",
"uuid": "6a173b84-bd2c-42c2-8dcd-5723df23aa56",
"title": "EP250827b / AT 2025wkm: TRT optical observations",
"submitter": "L. B. He at NAOC <helb@bao.ac.cn>",
"authors": "L. B. He at NAOC <helb@bao.ac.cn>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41671"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41671....1H",
"eventId": "EP250827b",
"subject": "EP250827b / AT 2025wkm: TRT optical observations",
"version": 2,
"editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of L. B. He at NAOC <helb@bao.ac.cn>",
"editedOn": 1756913724610,
"createdOn": 1756911998049,
"submitter": "L. B. He at NAOC <helb@bao.ac.cn>",
"circularId": 41671,
"submittedHow": "web"
},
"message_text": "L.B. He (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Y. Fu (HUST), J. An, X. Liu, Z.P. Zhu, S.Q. Jiang, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration:\n\nWe followed up the optical transient AT 2025wkm, which is potentially associated with EP250827b (Schroeder et al., GCN 41635). Our first epoch was carried out at the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, U.S.A (SRO), approximately 5.04 days after the EP X-ray flare. And we obtained several frames in the R band.\n\nThe counterpart (Schroder et al., GCN 41635; Hall et al., GCN 41636; Hall et al., GCN 41641; Eyles-Ferris et al., GCN 41655; Ma et al., GCN 41667; Eyles-Ferris et al., GCN 41669) was clearly detected in the stacked image, with R = 19.62 +/- 0.04 (Vega), calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction.",
"published": "2025-09-22T08:08:48.278131Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:48.278141Z",
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{
"id": 5775230,
"topic": "gcn.circulars",
"uuid": "2c6c79f0-0759-4547-a1b8-b75942ac83ba",
"title": "EP250827b / AT 2025wkm: TRT optical observations",
"submitter": "L. B. He at NAOC <helb@bao.ac.cn>",
"authors": "L. B. He at NAOC <helb@bao.ac.cn>",
"data": {
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"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827b",
"subject": "EP250827b / AT 2025wkm: TRT optical observations",
"createdOn": 1756911998049,
"submitter": "L. B. He at NAOC <helb@bao.ac.cn>",
"circularId": 41671,
"submittedHow": "web"
},
"message_text": "L.B. He (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Y. Fu (HUST), J. An, X. Liu, Z.P. Zhu, S.Q. Jiang, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration:\n\nWe followed up the optical transient AT 2025wkm, which is potentially associated with EP250827b (Schroeder et al., GCN 41635). Our first epoch was carried out at the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, U.S.A (SRO). And we obtained several frames in the R band.\n\nThe counterpart (Schroder et al., GCN 41635; Hall et al., GCN 41636; Hall et al., GCN 41641; Eyles-Ferris et al., GCN 41655; Ma et al., GCN 41667; Eyles-Ferris et al., GCN 41669) was clearly detected in the stacked image, with R = 19.62 +/- 0.04 (Vega), calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction.",
"published": "2025-09-03T15:06:48.059665Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-03T15:06:48.059689Z",
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{
"id": 5780844,
"topic": "gcn.circulars",
"uuid": "b81563bf-e934-4fa6-9ea8-a0b4fdb4ce75",
"title": "EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm",
"submitter": "Tomas Ahumada at Caltech <tfahumada94@gmail.com>",
"authors": "Tomas Ahumada at Caltech <tfahumada94@gmail.com>",
"data": {
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"bibcode": "2025GCN.41635....1S",
"eventId": "EP250827b",
"subject": "EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm",
"createdOn": 1756754445237,
"submitter": "Tomas Ahumada at Caltech <tfahumada94@gmail.com>",
"circularId": 41635,
"submittedHow": "web"
},
"message_text": "\nG. Schroeder (Cornell), T. Ahumada (Caltech), A. Y. Q. Ho (Cornell), M. Kasliwal (Caltech), L.Yan (Caltech), G. Srinivasaragavan (UMD), X. J. Hall (CMU), M. Coughlin (UMN), D. Y. Li (NAO, CAS), J. Yang (ZZU), X. Tian (GXU), K.R., Ni, (CCNU), H. L., Peng (NJNU), H. Y, Liu, Y. J., Song, H. Sun, Y. Liu, C.C.Jin, W. Yuan (NAO, CAS) on behalf of the Zwicky Transient Facility and Einstein Probe (EP) Partnership\n\nWe report the contemporaneous detection of the X-ray flare EP250827b associated with the optical transient ZTF25abmpngy/AT 2025wkm (RA = 02:26:20.64, Dec = +37:29:59.90). This event was highlighted in the cross-matching of ZTF alerts with EP alerts, an experiment first announced in Ahumada et al (GCN 39791). \n\nZTF25abmpngy/AT 2025wkm was first detected on 2025-08-27T09:38:04 UT, 3.27 hrs after the X-ray flare, and with an r-band apparent magnitude of r = 20.33 +/- 0.11 mag. We note the transient sits on top of a potential host galaxy with no archival spectroscopic redshift. \n \nEP250827b was first detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission at RA.= 36.581, DEC.= 37.499, with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic). The X-ray detection is 14.7 arcseconds away from the optical position. The X-ray transient started at 2025-08-27T06:22:27 (UT), and lasted for more than 1000 seconds as seen from the WXT light curve. The X-ray spectrum can be fitted by an absorbed power law model, with the absorption fixed at the Galactic value of 5.4x10^20 cm^-2 , and a photon index of 2.2 (-0.7, +0.8). The average unabsorbed 0.5-4keV flux is 2.6 (-0.9, +1.3) x 10^-11 erg/s/cm2. In the follow-up WXT coverage approximately 5 hours later at the position, the source was no longer detected, indicating a fast decay in the soft X-ray band.\n\n\nWe performed a follow-up target of opportunity observation with EP-FXT. The observation began at 2025-09-01T02:35:49 with an exposure time of 2995 seconds, about 5 days after the burst detected by EP-WXT. Within the WXT error circle, no X-ray source was detected at the optical position, setting a flux upper limit at 90% confidence level around 5 x 10^-14 erg/s/cm2. Based on the current temporal and spatial consistency, EP250827b is likely associated with AT2025wkn. However, due to the significant systematic uncertainty in the WXT position and the non-detection in the follow-up FXT observation, this association cannot be fully confirmed. \n\n\nWe are pursuing and encouraging follow-up observations to classify the source and validate the X-ray and optical association. \n \nLaunched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). \n \n \nBased on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; Operations are conducted by Caltech's Optical Observatory (COO) and Caltech/IPAC. \n \n \n \n \n",
"published": "2025-09-22T08:08:46.443805Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:46.443814Z",
"modified": "2025-09-22T08:08:46.447142Z",
"nonlocalizedevents": [],
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},
{
"id": 5774539,
"topic": "gcn.circulars",
"uuid": "e1a2f7ee-edca-4757-97b4-02a9faed2e7a",
"title": "EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm",
"submitter": "Tomas Ahumada at Caltech <tfahumada94@gmail.com>",
"authors": "Tomas Ahumada at Caltech <tfahumada94@gmail.com>",
"data": {
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"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827b",
"subject": "EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm",
"createdOn": 1756754445237,
"submitter": "Tomas Ahumada at Caltech <tfahumada94@gmail.com>",
"circularId": 41635,
"submittedHow": "web"
},
"message_text": "\nG. Schroeder (Cornell), T. Ahumada (Caltech), A. Y. Q. Ho (Cornell), M. Kasliwal (Caltech), L.Yan (Caltech), G. Srinivasaragavan (UMD), X. J. Hall (CMU), M. Coughlin (UMN), D. Y. Li (NAO, CAS), J. Yang (ZZU), X. Tian (GXU), K.R., Ni, (CCNU), H. L., Peng (NJNU), H. Y, Liu, Y. J., Song, H. Sun, Y. Liu, C.C.Jin, W. Yuan (NAO, CAS) on behalf of the Zwicky Transient Facility and Einstein Probe (EP) Partnership\n\nWe report the contemporaneous detection of the X-ray flare EP250827b associated with the optical transient ZTF25abmpngy/AT 2025wkm (RA = 02:26:20.64, Dec = +37:29:59.90). This event was highlighted in the cross-matching of ZTF alerts with EP alerts, an experiment first announced in Ahumada et al (GCN 39791). \n\nZTF25abmpngy/AT 2025wkm was first detected on 2025-08-27T09:38:04 UT, 3.27 hrs after the X-ray flare, and with an r-band apparent magnitude of r = 20.33 +/- 0.11 mag. We note the transient sits on top of a potential host galaxy with no archival spectroscopic redshift. \n \nEP250827b was first detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission at RA.= 36.581, DEC.= 37.499, with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic). The X-ray detection is 14.7 arcseconds away from the optical position. The X-ray transient started at 2025-08-27T06:22:27 (UT), and lasted for more than 1000 seconds as seen from the WXT light curve. The X-ray spectrum can be fitted by an absorbed power law model, with the absorption fixed at the Galactic value of 5.4x10^20 cm^-2 , and a photon index of 2.2 (-0.7, +0.8). The average unabsorbed 0.5-4keV flux is 2.6 (-0.9, +1.3) x 10^-11 erg/s/cm2. In the follow-up WXT coverage approximately 5 hours later at the position, the source was no longer detected, indicating a fast decay in the soft X-ray band.\n\n\nWe performed a follow-up target of opportunity observation with EP-FXT. The observation began at 2025-09-01T02:35:49 with an exposure time of 2995 seconds, about 5 days after the burst detected by EP-WXT. Within the WXT error circle, no X-ray source was detected at the optical position, setting a flux upper limit at 90% confidence level around 5 x 10^-14 erg/s/cm2. Based on the current temporal and spatial consistency, EP250827b is likely associated with AT2025wkn. However, due to the significant systematic uncertainty in the WXT position and the non-detection in the follow-up FXT observation, this association cannot be fully confirmed. \n\n\nWe are pursuing and encouraging follow-up observations to classify the source and validate the X-ray and optical association. \n \nLaunched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). \n \n \nBased on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; Operations are conducted by Caltech's Optical Observatory (COO) and Caltech/IPAC. \n \n \n \n \n",
"published": "2025-09-01T19:20:52.284937Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-01T19:20:52.284957Z",
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},
{
"id": 5775195,
"topic": "gcn.circulars",
"uuid": "fdcfa960-d127-4d62-875f-eee8dc3d3d6f",
"title": "EP250827b: continued Liverpool Telescope observations",
"submitter": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"authors": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"data": {
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"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827b",
"subject": "EP250827b: continued Liverpool Telescope observations",
"createdOn": 1756901978201,
"submitter": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"circularId": 41669,
"submittedHow": "web"
},
"message_text": "R. A. J. Eyles-Ferris and R. L. C. Starling (U of Leicester) report on behalf of a larger collaboration:\n\nWe observed the position of EP250827b/AT 2025wkm (Schroeder et al., GCN 41635) with the 2m Liverpool Telescope using the IO:O instrument. We obtained a series of exposures in the SDSS u’g’r’i’z’ filters starting at 2025-09-03 01:45:07 UT, approximately 162.5 hours after the X-ray detection.\n\nWe performed image subtraction on the stacked g’r’i’z’ images using reference images from Pan-STARRS. AT 2025wkm is clearly detected in all our subtractions and appears to be currently rising in all bands. We measure r’ = 19.90 +/- 0.05, calibrated to Pan-STARRS and not corrected for Galactic extinction, which corresponds to an absolute magnitude of -18.91 adopting the redshift of 0.120 of Sevilla and Ho (GCN 41639). We note no significant change in colour (g’ - r’ ~ 0) when compared with our earlier epoch photometry (Eyles-Ferris and Starling, GCN 41655).\n\nFurther observations are planned.",
"published": "2025-09-03T12:19:46.457225Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-03T12:19:46.457247Z",
"modified": "2025-09-03T12:19:46.478553Z",
"nonlocalizedevents": [],
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},
{
"id": 5781067,
"topic": "gcn.circulars",
"uuid": "5c283853-e291-4f78-a1a5-f1d358bab209",
"title": "EP250827b: continued Liverpool Telescope observations",
"submitter": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"authors": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"data": {
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"bibcode": "2025GCN.41669....1E",
"eventId": "EP250827b",
"subject": "EP250827b: continued Liverpool Telescope observations",
"createdOn": 1756901978201,
"submitter": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"circularId": 41669,
"submittedHow": "web"
},
"message_text": "R. A. J. Eyles-Ferris and R. L. C. Starling (U of Leicester) report on behalf of a larger collaboration:\n\nWe observed the position of EP250827b/AT 2025wkm (Schroeder et al., GCN 41635) with the 2m Liverpool Telescope using the IO:O instrument. We obtained a series of exposures in the SDSS u’g’r’i’z’ filters starting at 2025-09-03 01:45:07 UT, approximately 162.5 hours after the X-ray detection.\n\nWe performed image subtraction on the stacked g’r’i’z’ images using reference images from Pan-STARRS. AT 2025wkm is clearly detected in all our subtractions and appears to be currently rising in all bands. We measure r’ = 19.90 +/- 0.05, calibrated to Pan-STARRS and not corrected for Galactic extinction, which corresponds to an absolute magnitude of -18.91 adopting the redshift of 0.120 of Sevilla and Ho (GCN 41639). We note no significant change in colour (g’ - r’ ~ 0) when compared with our earlier epoch photometry (Eyles-Ferris and Starling, GCN 41655).\n\nFurther observations are planned.",
"published": "2025-09-22T08:08:52.719397Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:52.719405Z",
"modified": "2025-09-22T08:08:52.722896Z",
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{
"id": 5780925,
"topic": "gcn.circulars",
"uuid": "91324ee6-3089-4c29-8063-88d8ddf18e5e",
"title": "EP 250827B: Detection of supernova counterpart by LCO.",
"submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"authors": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"data": {
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},
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"bibcode": "2025GCN.41673....1G",
"eventId": "EP250827b",
"subject": "EP 250827B: Detection of supernova counterpart by LCO.",
"version": 2,
"editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"editedOn": 1756922170301,
"createdOn": 1756913683495,
"submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"circularId": 41673,
"submittedHow": "web"
},
"message_text": "Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES)on behalf of a larger collaboration.\n \nWe observed the field of the EP250827B/AT 2025wkm (Schroeder et al., GCN 41635) in V, r filter of the 0.4-m SCICAM QHY600 at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Haleakala Observatory, Hawai . The 0.4 m SCICAM QHY600 is equipped with 9576 x 6388 pixel CCD (FOV: 1.9 x 1.2 degrees, scale: 0.74 arcsec/pixel) but we only used the FOV of 30 x 30 arcmin for our observation. Observations began on September 03, 2025, starting 7.32 days after the GRB trigger. Further observations are currently ongoing.\n\nWe clearly detect the optical transient (OT) reported by GCNs (Schroder et al., GCN 41635; Hall et al., GCN 41636; Hall et al., GCN 41641; Eyles-Ferris et al., GCN 41655; Ma et al., GCN 41667; Eyles-Ferris et al., GCN 41669, He et al,. GCN 41671) in our r band image. Corcoran et al. GCN 41670. reported the detection of the rise of the associated Ic-BL supernova.\n\n|Date|\t\t|UTstart|\t|t-T0 (days)|\t|Exp (sec)|\t|Filter|\t|Magnitude| \n-------------------------------------------------------------------------------------------------- \n2025-09-03\t13:58:49.728\t7.32\t\t3 x 900 \tr\t r = 19.81 +/- 0.05\n\n\nThe field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.\n",
"published": "2025-09-22T08:08:48.286656Z",
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"retracted": false,
"created": "2025-09-22T08:08:48.286664Z",
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},
{
"id": 5775263,
"topic": "gcn.circulars",
"uuid": "2201929e-b9fa-4992-86c2-62763ed403b5",
"title": "EP 250827B: Detection of supernova counterpart by LCO.",
"submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"authors": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"data": {
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"eventId": "EP250827b",
"subject": "EP 250827B: Detection of supernova counterpart by LCO.",
"version": 2,
"editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
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"submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"circularId": 41673,
"submittedHow": "web"
},
"message_text": "Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES)on behalf of a larger collaboration.\n \nWe observed the field of the EP250827B/AT 2025wkm (Schroeder et al., GCN 41635) in V, r filter of the 0.4-m SCICAM QHY600 at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Haleakala Observatory, Hawai . The 0.4 m SCICAM QHY600 is equipped with 9576 x 6388 pixel CCD (FOV: 1.9 x 1.2 degrees, scale: 0.74 arcsec/pixel) but we only used the FOV of 30 x 30 arcmin for our observation. Observations began on September 03, 2025, starting 7.32 days after the GRB trigger. Further observations are currently ongoing.\n\nWe clearly detect the optical transient (OT) reported by GCNs (Schroder et al., GCN 41635; Hall et al., GCN 41636; Hall et al., GCN 41641; Eyles-Ferris et al., GCN 41655; Ma et al., GCN 41667; Eyles-Ferris et al., GCN 41669, He et al,. GCN 41671) in our r band image. Corcoran et al. GCN 41670. reported the detection of the rise of the associated Ic-BL supernova.\n\n|Date|\t\t|UTstart|\t|t-T0 (days)|\t|Exp (sec)|\t|Filter|\t|Magnitude| \n-------------------------------------------------------------------------------------------------- \n2025-09-03\t13:58:49.728\t7.32\t\t3 x 900 \tr\t r = 19.81 +/- 0.05\n\n\nThe field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.\n",
"published": "2025-09-03T17:56:15.661838Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-03T17:56:15.661859Z",
"modified": "2025-09-03T17:56:15.678421Z",
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},
{
"id": 5775235,
"topic": "gcn.circulars",
"uuid": "db9e1fa7-7a4a-42e3-ace6-67fc74595c77",
"title": "EP 250827B: Detection of the fading supernova counterpart by LCO.",
"submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"authors": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"data": {
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"eventId": "EP250827b",
"subject": "EP 250827B: Detection of the fading supernova counterpart by LCO.",
"createdOn": 1756913683495,
"submitter": "ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>",
"circularId": 41673,
"submittedHow": "web"
},
"message_text": "Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES)on behalf of a larger collaboration.\n \nWe observed the field of the EP250827B/AT 2025wkm (Schroeder et al., GCN 41635) in V, r filter of the 0.4-m SCICAM QHY600 at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Haleakala Observatory, Hawai . The 0.4 m SCICAM QHY600 is equipped with 9576 x 6388 pixel CCD (FOV: 1.9 x 1.2 degrees, scale: 0.74 arcsec/pixel) but we only used the FOV of 30 x 30 arcmin for our observation. Observations began on September 03, 2025, starting 7.32 days after the GRB trigger. Further observations are currently ongoing.\n\n\nWe clearly detect the optical transient (OT) reported by GCNs (Schroder et al., GCN 41635; Hall et al., GCN 41636; Hall et al., GCN 41641; Eyles-Ferris et al., GCN 41655; Ma et al., GCN 41667; Eyles-Ferris et al., GCN 41669, He et al,. GCN 41671) in our r band image. Eyles-Ferris et al., GCN 41655 reported the detection of the rise of the associated Ic-BL supernova, with a measured magnitude of 18.91 at 5.61 days after the explosion. The source subsequently faded by ~1 mag within 1.71 days.\n\n\n|Date|\t\t|UTstart|\t|t-T0 (days)|\t|Exp (sec)|\t|Filter|\t|Magnitude| \n-------------------------------------------------------------------------------------------------- \n2025-09-03\t13:58:49.728\t7.32\t\t3 x 900 \tr\t r = 19.81 +/- 0.05\n\n\nThe field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.\n",
"published": "2025-09-03T15:34:52.881281Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-03T15:34:52.881304Z",
"modified": "2025-09-03T15:34:52.897538Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5780845,
"topic": "gcn.circulars",
"uuid": "5243fad8-8040-491e-ada8-a741e70d496d",
"title": "EP250827b: FTW Observations of AT 2025wkm",
"submitter": "xjh@andrew.cmu.edu",
"authors": "xjh@andrew.cmu.edu",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41636"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41636....1H",
"eventId": "EP250827b",
"subject": "EP250827b: FTW Observations of AT 2025wkm",
"createdOn": 1756755016629,
"submitter": "xjh@andrew.cmu.edu",
"circularId": 41636,
"submittedHow": "web"
},
"message_text": "Xander J. Hall (Carnegie Mellon U.), Malte Busmann (LMU), Daniel Gruen (LMU), Brendan O’Connor (Carnegie Mellon U.), Antonella Palmese (Carnegie Mellon U.), Mansi Kasliwal (Caltech), Tomas Ahumada (Caltech), and Gokul Srinivasaragavan (UMD) report:\n\nWe observed the localization of the X-ray flare EP250827b and optical transient AT 2025wkm as reported by Schroeder et al. (GCN 41635), with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J bands starting at 2025-08-31T02:01:59 UTC (3.82 days after the X-ray flare) for 24 x 180s. In the difference imaging with templates from PS1, we detect AT 2025wkm at\n\nr = 20.14 +/- 0.02 AB mag,\n\nThe magnitudes are calibrated against the PS1 catalog and not corrected for Galactic extinction.\n\nFurthermore, we see no other candidates in the difference imaging to a limiting depth of r = 23.15, which supports the association of AT 2025wkn and EP250827b. Further analysis is underway.\n\nWe thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations.",
"published": "2025-09-22T08:08:46.452969Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:46.452977Z",
"modified": "2025-09-22T08:08:46.456294Z",
"nonlocalizedevents": [],
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},
{
"id": 5774542,
"topic": "gcn.circulars",
"uuid": "167301a5-04ce-4478-9fd5-974c10b39f94",
"title": "EP250827b: FTW Observations of AT 2025wkm",
"submitter": "xjh@andrew.cmu.edu",
"authors": "xjh@andrew.cmu.edu",
"data": {
"urls": {
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},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827b",
"subject": "EP250827b: FTW Observations of AT 2025wkm",
"createdOn": 1756755016629,
"submitter": "xjh@andrew.cmu.edu",
"circularId": 41636,
"submittedHow": "web"
},
"message_text": "Xander J. Hall (Carnegie Mellon U.), Malte Busmann (LMU), Daniel Gruen (LMU), Brendan O’Connor (Carnegie Mellon U.), Antonella Palmese (Carnegie Mellon U.), Mansi Kasliwal (Caltech), Tomas Ahumada (Caltech), and Gokul Srinivasaragavan (UMD) report:\n\nWe observed the localization of the X-ray flare EP250827b and optical transient AT 2025wkm as reported by Schroeder et al. (GCN 41635), with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J bands starting at 2025-08-31T02:01:59 UTC (3.82 days after the X-ray flare) for 24 x 180s. In the difference imaging with templates from PS1, we detect AT 2025wkm at\n\nr = 20.14 +/- 0.02 AB mag,\n\nThe magnitudes are calibrated against the PS1 catalog and not corrected for Galactic extinction.\n\nFurthermore, we see no other candidates in the difference imaging to a limiting depth of r = 23.15, which supports the association of AT 2025wkn and EP250827b. Further analysis is underway.\n\nWe thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations.",
"published": "2025-09-01T19:30:24.955981Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-01T19:30:24.956006Z",
"modified": "2025-09-01T19:30:24.984560Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5775888,
"topic": "gcn.circulars",
"uuid": "08f5e7c6-01e0-4671-b6f2-de9b13d84d39",
"title": "EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova",
"submitter": "Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"authors": "Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"data": {
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"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827b",
"subject": "EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova",
"version": 2,
"editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"editedOn": 1757078483156,
"createdOn": 1757008437633,
"submitter": "Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"circularId": 41705,
"submittedHow": "web"
},
"message_text": "Brendan O’Connor (CMU), Xander J. Hall (CMU), Antonella Palmese (CMU), Daniel Gruen (LMU), Gokul Srinivasaragavan (UMD), Anna Y. Q. Ho (Cornell):\n\nWe observed the optical transient AT2025wkm, associated with EP250827b (Schroeder et al., GCN 41635), using GMOS mounted on Gemini-North (PI: O’Connor). Observations started on 2025-09-02 at 13:36:55 UT (6.3 d) and 2025-09-04 at 10:58:00 UT (8.2 d). At each epoch, we obtained 2x600 s exposures using the B480 grating covering 3950-8210 AA.\n\nThe spectra show a steep blueward slope (likely due to shock cooling) and display broad features that are consistent with ejecta moving at a high velocity (see also Corcoran et al., GCN 41670 and Ho et al., GCN 41639). We identify blueshifted Fe II absorption features in both spectra, indicative of ejecta velocities ~ 40,000 km/s. The Fe II absorption features in combination with the lack of broad Hydrogen and Helium features associated with the transient itself allow us to confirm the classification of a Ic-BL supernova as initially reported by Corcoran et al. (GCN 41670). In addition, we identify numerous narrow emission lines, including the [O II] doublet, multiple [Ne III] lines, the entire Balmer series between Heta and Halpha, He I lines, [N II], [S II], and [Ar III], that identify the host galaxy as highly star forming.\n\nFurther observations are planned and encouraged.\n\nWe thank the staff of the Gemini Observatory, in particular Brian Lemaux, Eunchong Kim, Teo Mocnik, and Aleksandar Cikota for their assistance in planning and obtaining these observations.\n",
"published": "2025-09-05T13:21:24.646500Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-05T13:21:24.646524Z",
"modified": "2025-09-05T13:21:24.649688Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5781069,
"topic": "gcn.circulars",
"uuid": "3ed11399-419b-4e6d-aed0-c9c9ae92b4ef",
"title": "EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova",
"submitter": "Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"authors": "Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"data": {
"urls": {
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},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41705....1O",
"eventId": "EP250827b",
"subject": "EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova",
"version": 2,
"editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"editedOn": 1757078483156,
"createdOn": 1757008437633,
"submitter": "Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"circularId": 41705,
"submittedHow": "web"
},
"message_text": "Brendan O’Connor (CMU), Xander J. Hall (CMU), Antonella Palmese (CMU), Daniel Gruen (LMU), Gokul Srinivasaragavan (UMD), Anna Y. Q. Ho (Cornell):\n\nWe observed the optical transient AT2025wkm, associated with EP250827b (Schroeder et al., GCN 41635), using GMOS mounted on Gemini-North (PI: O’Connor). Observations started on 2025-09-02 at 13:36:55 UT (6.3 d) and 2025-09-04 at 10:58:00 UT (8.2 d). At each epoch, we obtained 2x600 s exposures using the B480 grating covering 3950-8210 AA.\n\nThe spectra show a steep blueward slope (likely due to shock cooling) and display broad features that are consistent with ejecta moving at a high velocity (see also Corcoran et al., GCN 41670 and Ho et al., GCN 41639). We identify blueshifted Fe II absorption features in both spectra, indicative of ejecta velocities ~ 40,000 km/s. The Fe II absorption features in combination with the lack of broad Hydrogen and Helium features associated with the transient itself allow us to confirm the classification of a Ic-BL supernova as initially reported by Corcoran et al. (GCN 41670). In addition, we identify numerous narrow emission lines, including the [O II] doublet, multiple [Ne III] lines, the entire Balmer series between Heta and Halpha, He I lines, [N II], [S II], and [Ar III], that identify the host galaxy as highly star forming.\n\nFurther observations are planned and encouraged.\n\nWe thank the staff of the Gemini Observatory, in particular Brian Lemaux, Eunchong Kim, Teo Mocnik, and Aleksandar Cikota for their assistance in planning and obtaining these observations.\n",
"published": "2025-09-22T08:08:52.736832Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:52.736841Z",
"modified": "2025-09-22T08:08:52.740486Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5775622,
"topic": "gcn.circulars",
"uuid": "1697bfc2-7de4-4ced-afc4-4ec15f2a8f57",
"title": "EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova",
"submitter": "Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"authors": "Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"data": {
"urls": {
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},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827b",
"subject": "EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova",
"createdOn": 1757008437633,
"submitter": "Brendan O'Connor at Carnegie Mellon University <boconno2@andrew.cmu.edu>",
"circularId": 41705,
"submittedHow": "web"
},
"message_text": "Brendan O’Connor (CMU), Xander J. Hall (CMU), Antonella Palmese (CMU), Daniel Gruen (LMU), Gokul Srinivasaragavan (UMD), Anna Y. Q. Ho (Cornell):\n\nWe observed the optical transient AT2025wkm, associated with EP250827b (Schroeder et al., GCN 41635), using GMOS mounted on Gemini-North (PI: O’Connor). Observations started on 2025-09-02 at 13:36:55 UT (6.3 d) and 2025-09-04 at 10:58:00 UT (8.2 d). At each epoch, we obtained 2x600 s exposures using the B480 grating covering 3950-8210 AA.\n\nThe spectra show a steep blueward slope (likely due to shock cooling) and display broad features that are consistent with ejecta moving at a high velocity (see also Corcoran et al., GCN 41670 and Ho et al., GCN 41639). We identify blueshifted Fe II absorption features in both spectra, indicative of ejecta velocities ~ 40,000 km/s. The Fe II absorption features in combination with the lack of broad Hydrogen and Helium features associated with the transient itself allow us to confirm the classification of a Ic-BL supernova as initially reported by Corcoran et al. (GCN 41670). In addition, we identify numerous narrow emission lines, including the [O II] doublet, multiple [Ne III] lines, the entire Balmer series between Hbeta and Halpha, He I lines, [N II], [S II], and [Ar III], that identify the host galaxy as highly star forming.\n\nFurther observations are planned and encouraged.\n\nWe thank the staff of the Gemini Observatory, in particular Brian Lemaux, Eunchong Kim, Teo Mocnik, and Aleksandar Cikota for their assistance in planning and obtaining these observations.\n",
"published": "2025-09-04T17:54:04.127583Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-04T17:54:04.127605Z",
"modified": "2025-09-04T17:54:04.137775Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5780978,
"topic": "gcn.circulars",
"uuid": "a3eea38b-efb2-49ab-aa91-202f5c9ca2ac",
"title": "EP250827b: Gemini Spectroscopy of AT 2025wkm",
"submitter": "Anna Y Q Ho at Cornell University <ayh24@cornell.edu>",
"authors": "Anna Y Q Ho at Cornell University <ayh24@cornell.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41639"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41639....1S",
"eventId": "EP250827b",
"subject": "EP250827b: Gemini Spectroscopy of AT 2025wkm",
"createdOn": 1756758467026,
"submitter": "Anna Y Q Ho at Cornell University <ayh24@cornell.edu>",
"circularId": 41639,
"submittedHow": "web"
},
"message_text": "Cassie Sevilla and Anna Ho (Cornell) report on behalf of the ZTF collaboration:\n\nWe acquired long-slit spectroscopy of AT 2025wkm (possibly associated with Einstein Probe X-ray flare EP250827b; Schroeder et al. GCN #41635) using GMOS-N at Gemini Observatory on 2025-08-31 12:15:31 UTC, under the target-of-opportunity program GN-2025B-Q-130 (PI Ho). The observation was carried out with a 1\" slit, the R400 grating, and the GG455 filter. We took four 450s exposures, two at a central wavelength of 710 nm and two at 720 nm. The data was reduced using DRAGONS. \n\nThe spectrum shows a blue continuum with narrow emission lines of H alpha, H beta, [O III], and [S II] at a consistent redshift of z=0.120. The implied peak measured absolute magnitude of AT 2025wkm is M_g = -19.5 mag, corrected for Milky Way extinction. The rapid rise (~3d) to such a high luminosity is unusual for extragalactic transients.\n\nWe thank the Gemini Observatory staff for assistance in rapidly obtaining these observations.",
"published": "2025-09-22T08:08:49.793014Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:49.793021Z",
"modified": "2025-09-22T08:08:49.796368Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5774554,
"topic": "gcn.circulars",
"uuid": "1c56d432-cb3c-49ab-9432-8b3351a1f77a",
"title": "EP250827b: Gemini Spectroscopy of AT 2025wkm",
"submitter": "Anna Y Q Ho at Cornell University <ayh24@cornell.edu>",
"authors": "Anna Y Q Ho at Cornell University <ayh24@cornell.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41639"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827b",
"subject": "EP250827b: Gemini Spectroscopy of AT 2025wkm",
"createdOn": 1756758467026,
"submitter": "Anna Y Q Ho at Cornell University <ayh24@cornell.edu>",
"circularId": 41639,
"submittedHow": "web"
},
"message_text": "Cassie Sevilla and Anna Ho (Cornell) report on behalf of the ZTF collaboration:\n\nWe acquired long-slit spectroscopy of AT 2025wkm (possibly associated with Einstein Probe X-ray flare EP250827b; Schroeder et al. GCN #41635) using GMOS-N at Gemini Observatory on 2025-08-31 12:15:31 UTC, under the target-of-opportunity program GN-2025B-Q-130 (PI Ho). The observation was carried out with a 1\" slit, the R400 grating, and the GG455 filter. We took four 450s exposures, two at a central wavelength of 710 nm and two at 720 nm. The data was reduced using DRAGONS. \n\nThe spectrum shows a blue continuum with narrow emission lines of H alpha, H beta, [O III], and [S II] at a consistent redshift of z=0.120. The implied peak measured absolute magnitude of AT 2025wkm is M_g = -19.5 mag, corrected for Milky Way extinction. The rapid rise (~3d) to such a high luminosity is unusual for extragalactic transients.\n\nWe thank the Gemini Observatory staff for assistance in rapidly obtaining these observations.",
"published": "2025-09-01T20:27:54.197644Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-01T20:27:54.197660Z",
"modified": "2025-09-01T20:27:54.218295Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5774718,
"topic": "gcn.circulars",
"uuid": "7d533039-f7b8-4385-9ae5-e0da8146bc1b",
"title": "EP250827b: Liverpool Telescope observations",
"submitter": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"authors": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41655"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827b",
"subject": "EP250827b: Liverpool Telescope observations",
"createdOn": 1756800417023,
"submitter": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"circularId": 41655,
"submittedHow": "web"
},
"message_text": "R. A. J. Eyles-Ferris and R. L. C. Starling (U of Leicester) report on behalf of a larger collaboration:\n\nWe observed the position of EP250827b/AT 2025wkm (Schroeder et al., GCN 41635) with the 2m Liverpool Telescope using the IO:O instrument. We obtained a series of exposures in the SDSS u’g’r’i’z’ filters starting at 2025-09-02 02:47:47 UT, approximately 139.5 hours after the X-ray detection.\n\nWe performed image subtraction on the stacked g’r’i’z’ images using reference images from Pan-STARRS. We clearly detect a source consistent with AT 2025wkm in all our subtractions and measure r’ = 19.97 +/- 0.04. Our measured magnitude compared to Schroeder et al. (GCN 41635) and Hall et al. (GCN 41636) suggests AT 2025wkm may still be rising in the r band. The colour of the source (g’ - r’ ~ 0.0) is consistent with the blue spectrum observed by Sevilla and Ho (GCN 41639).\n\nFurther observations are planned.",
"published": "2025-09-02T08:07:06.177468Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-02T08:07:06.177485Z",
"modified": "2025-09-02T08:07:06.188725Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5780922,
"topic": "gcn.circulars",
"uuid": "a20f5bd4-e2fb-48d3-9da2-94260f627d89",
"title": "EP250827b: Liverpool Telescope observations",
"submitter": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"authors": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41655"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41655....1E",
"eventId": "EP250827b",
"subject": "EP250827b: Liverpool Telescope observations",
"createdOn": 1756800417023,
"submitter": "Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>",
"circularId": 41655,
"submittedHow": "web"
},
"message_text": "R. A. J. Eyles-Ferris and R. L. C. Starling (U of Leicester) report on behalf of a larger collaboration:\n\nWe observed the position of EP250827b/AT 2025wkm (Schroeder et al., GCN 41635) with the 2m Liverpool Telescope using the IO:O instrument. We obtained a series of exposures in the SDSS u’g’r’i’z’ filters starting at 2025-09-02 02:47:47 UT, approximately 139.5 hours after the X-ray detection.\n\nWe performed image subtraction on the stacked g’r’i’z’ images using reference images from Pan-STARRS. We clearly detect a source consistent with AT 2025wkm in all our subtractions and measure r’ = 19.97 +/- 0.04. Our measured magnitude compared to Schroeder et al. (GCN 41635) and Hall et al. (GCN 41636) suggests AT 2025wkm may still be rising in the r band. The colour of the source (g’ - r’ ~ 0.0) is consistent with the blue spectrum observed by Sevilla and Ho (GCN 41639).\n\nFurther observations are planned.",
"published": "2025-09-22T08:08:48.259894Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:48.259902Z",
"modified": "2025-09-22T08:08:48.263426Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5780983,
"topic": "gcn.circulars",
"uuid": "fb0845ec-8cd9-4b66-bb43-14a810d9d2f4",
"title": "EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova",
"submitter": "Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>",
"authors": "Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41670"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41670....1C",
"eventId": "EP250827b",
"subject": "EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova",
"version": 2,
"editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>",
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"submitter": "Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>",
"circularId": 41670,
"submittedHow": "web"
},
"message_text": "G. Corcoran (UCD), A. J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), R. A. J. Eyles-Ferris (Leicester), V. Vuolteenaho (NOT and Oulu Univ.), M. Pursiainen (Warwick), I. Worssam (Birmingham) report:\n\nWe carried out two spectroscopic observations of the optical transient AT 2025wkm (Schroeder et al., GCN 41635) likely associated with the Einstein Probe transient EP250827b, using the ALFOSC spectrograph mounted on the Nordic Optical Telescope (NOT). The observations started on 2025-09-02 at 00:31:54 and 2025-09-03 at 04:37:19 UT for the two epochs, respectively (5.76 and 6.93 days after the EP trigger). Both observations consisted of 4 x 900 s exposures and cover the wavelength range 3800-9500 AA.\n\nBoth spectra show features consistent with broad-lined type Ic supernovae at a comparable phase, though with an excess of flux on the blue end, providing a good match to the super-luminous SN 2011kl (associated with GRB 111209A; Greiner et al. 2015, doi:10.1038/nature14579) near peak. The brightness of the source, at an absolute magnitude of M_r = -18.91 and still rising (Eyles-Ferris & Starling, GCN 41669), is currently consistent with classification as both a normal Ic-BL SN and a super-luminous SN. Between the two epochs, we also identify no significant spectral evolution consistent with the constant colour observed by Eyles-Ferris & Starling (GCN 41669).\n\nFurther photometric and spectroscopic observations are planned and encouraged to better characterize this interesting source.\n",
"published": "2025-09-22T08:08:49.834422Z",
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{
"id": 5775205,
"topic": "gcn.circulars",
"uuid": "cafeb3d2-1c51-437b-8a5a-0f7fef85ffcf",
"title": "EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova",
"submitter": "Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>",
"authors": "Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>",
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"submitter": "Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>",
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"submittedHow": "web"
},
"message_text": "G. Corcoran (UCD), A. J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), R. A. J. Eyles-Ferris (Leicester), V. Vuolteenaho (NOT and Oulu Univ.), M. Pursiainen (Warwick), I. Worssam (Birmingham) report:\n\nWe carried out two spectroscopic observations of the optical transient AT 2025wkm (Schroeder et al., GCN 41635) likely associated with the Einstein Probe transient EP250827b, using the ALFOSC spectrograph mounted on the Nordic Optical Telescope (NOT). The observations started on 2025-09-02 at 00:31:54 and 2025-09-03 at 04:37:19 UT for the two epochs, respectively (5.76 and 6.93 days after the EP trigger). Both observations consisted of 4 x 900 s exposures and cover the wavelength range 3800-9500 AA.\n\nBoth spectra show features consistent with broad-lined type Ic supernovae at a comparable phase, though with an excess of flux on the blue end, providing a good match to the super-luminous SN 2011kl (associated with GRB 111209A; Greiner et al. 2015, doi:10.1038/nature14579) near peak. The brightness of the source, at an absolute magnitude of r = -18.91 and still rising (Eyles-Ferris & Starling, GCN 41669), is currently consistent with classification as both a normal Ic-BL SN and a super-luminous SN. Between the two epochs, we also identify no significant spectral evolution consistent with the constant colour observed by Eyles-Ferris & Starling (GCN 41669).\n\nFurther photometric and spectroscopic observations are planned and encouraged to better characterize this interesting source.\n",
"published": "2025-09-03T13:24:30.399615Z",
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{
"id": 5775501,
"topic": "gcn.circulars",
"uuid": "8b150dff-6f0e-4402-ab3a-e99519e2707a",
"title": "EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova",
"submitter": "Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>",
"authors": "Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>",
"data": {
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"eventId": "EP250827b",
"subject": "EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova",
"version": 2,
"editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>",
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"submitter": "Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>",
"circularId": 41670,
"submittedHow": "web"
},
"message_text": "G. Corcoran (UCD), A. J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), R. A. J. Eyles-Ferris (Leicester), V. Vuolteenaho (NOT and Oulu Univ.), M. Pursiainen (Warwick), I. Worssam (Birmingham) report:\n\nWe carried out two spectroscopic observations of the optical transient AT 2025wkm (Schroeder et al., GCN 41635) likely associated with the Einstein Probe transient EP250827b, using the ALFOSC spectrograph mounted on the Nordic Optical Telescope (NOT). The observations started on 2025-09-02 at 00:31:54 and 2025-09-03 at 04:37:19 UT for the two epochs, respectively (5.76 and 6.93 days after the EP trigger). Both observations consisted of 4 x 900 s exposures and cover the wavelength range 3800-9500 AA.\n\nBoth spectra show features consistent with broad-lined type Ic supernovae at a comparable phase, though with an excess of flux on the blue end, providing a good match to the super-luminous SN 2011kl (associated with GRB 111209A; Greiner et al. 2015, doi:10.1038/nature14579) near peak. The brightness of the source, at an absolute magnitude of M_r = -18.91 and still rising (Eyles-Ferris & Starling, GCN 41669), is currently consistent with classification as both a normal Ic-BL SN and a super-luminous SN. Between the two epochs, we also identify no significant spectral evolution consistent with the constant colour observed by Eyles-Ferris & Starling (GCN 41669).\n\nFurther photometric and spectroscopic observations are planned and encouraged to better characterize this interesting source.\n",
"published": "2025-09-04T12:27:31.161456Z",
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"retracted": false,
"created": "2025-09-04T12:27:31.161479Z",
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{
"id": 5775123,
"topic": "gcn.circulars",
"uuid": "e5cc0df6-05f2-44d0-b24a-4dc857467e61",
"title": "EP250827b: SVOM/VT observation of AT 2025wkm",
"submitter": "Yinuo Ma <mayn@bao.ac.cn>",
"authors": "Yinuo Ma <mayn@bao.ac.cn>",
"data": {
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"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827b",
"subject": "EP250827b: SVOM/VT observation of AT 2025wkm",
"createdOn": 1756875892616,
"submitter": "Yinuo Ma <mayn@bao.ac.cn>",
"circularId": 41667,
"submittedHow": "web"
},
"message_text": "Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. \n\nSVOM performed a Target of Opportunity observation of EP250827b/AT 2025wkm (Schroeder et al., GCN 41635). SVOM/VT began observing the field at 2025-09-02T09:14:40 UTC, 6.12 days after the X-ray detection, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. \n\nWith X-band data availible, the source consistent with AT 2025wkm (Schroeder et al., GCN 41635; Hall et al., GCN 41636; Sevilla & Ho, GCN 41639; Hall et al., GCN 41641; Eyles-Ferris & Starling, GCN 41655) was clearly detected in both VT_B and VT_R. However, the source in VT_R was contaminated by the blooming of bright star, so the magnitude of VT_B is:\n\nmid time (day) | exposure time (s) | band | mag (AB) | mag err\n---------------|-------------------|------|----------|--------\n 6.24 | 37*70 | VT_B | 19.81 | 0.03 \n\nOur photometry was not corrected for Galactic extinction.\n\nThe Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.\n",
"published": "2025-09-03T05:05:02.047102Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-03T05:05:02.047123Z",
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},
{
"id": 5780809,
"topic": "gcn.circulars",
"uuid": "93967189-f316-4af2-9a2d-d812aacfdfee",
"title": "EP250827b: SVOM/VT observation of AT 2025wkm",
"submitter": "Yinuo Ma <mayn@bao.ac.cn>",
"authors": "Yinuo Ma <mayn@bao.ac.cn>",
"data": {
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"bibcode": "2025GCN.41667....1M",
"eventId": "EP250827b",
"subject": "EP250827b: SVOM/VT observation of AT 2025wkm",
"createdOn": 1756875892616,
"submitter": "Yinuo Ma <mayn@bao.ac.cn>",
"circularId": 41667,
"submittedHow": "web"
},
"message_text": "Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. \n\nSVOM performed a Target of Opportunity observation of EP250827b/AT 2025wkm (Schroeder et al., GCN 41635). SVOM/VT began observing the field at 2025-09-02T09:14:40 UTC, 6.12 days after the X-ray detection, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. \n\nWith X-band data availible, the source consistent with AT 2025wkm (Schroeder et al., GCN 41635; Hall et al., GCN 41636; Sevilla & Ho, GCN 41639; Hall et al., GCN 41641; Eyles-Ferris & Starling, GCN 41655) was clearly detected in both VT_B and VT_R. However, the source in VT_R was contaminated by the blooming of bright star, so the magnitude of VT_B is:\n\nmid time (day) | exposure time (s) | band | mag (AB) | mag err\n---------------|-------------------|------|----------|--------\n 6.24 | 37*70 | VT_B | 19.81 | 0.03 \n\nOur photometry was not corrected for Galactic extinction.\n\nThe Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.\n",
"published": "2025-09-22T08:08:42.032711Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:42.032719Z",
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{
"id": 5780888,
"topic": "gcn.circulars",
"uuid": "0e139f7e-2279-41ca-977c-d4bde3c41c74",
"title": "EP250827b: Swift observations of AT 2025wkm",
"submitter": "xjh@andrew.cmu.edu",
"authors": "xjh@andrew.cmu.edu",
"data": {
"urls": {
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},
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"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41641....1H",
"eventId": "EP250827b",
"subject": "EP250827b: Swift observations of AT 2025wkm",
"createdOn": 1756760251338,
"submitter": "xjh@andrew.cmu.edu",
"circularId": 41641,
"submittedHow": "web"
},
"message_text": "Xander J. Hall (Carnegie Mellon U.), Tomas Ahumada (Caltech), and Robert Stein (UMD) on behalf of the ZTF collaboration:\n\nWe requested Swift ToO observations of the X-ray flare EP250827b and optical transient AT 2025wkm reported by Schroeder et al. (GCN 41635).\n\nThe observation was taken with a midpoint time of 2025-08-31 at 21:13:29 UT, approximately 4.62 days after the flare, with a duration of 4ks.\n\nThe source was not detected with XRT with an upper limit of 2.5 * 10^-3 cts/s at 0.3 - 10 keV. Given the redshift reported by Sevilla & Ho (GCN 41639) of z = 0.1200 this gives a rough luminosity upper limit of 4.5 * 10^42 erg/s. \n\nWe clearly detect a source at the position of AT 2025wkm in UVOT observations. We use a synthetic galaxy model to produce subtracted magnitudes and correct for galactic extinction. We report in the UVW1 filter, a magnitude of m= 21.7 +/- 0.4 AB and in the UVM2 filter, a magnitude of m = 22.2 +/- 0.3.\n\nWe thank the Swift team, Observatory Duty Scientists and the PI for promptly scheduling and making these observations possible.\n",
"published": "2025-09-22T08:08:46.900079Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:46.900088Z",
"modified": "2025-09-22T08:08:46.903654Z",
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},
{
"id": 5774561,
"topic": "gcn.circulars",
"uuid": "328734df-2dd8-4d60-8350-35ce69d3df5d",
"title": "EP250827b: Swift observations of AT 2025wkm",
"submitter": "xjh@andrew.cmu.edu",
"authors": "xjh@andrew.cmu.edu",
"data": {
"urls": {
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"eventId": "EP250827b",
"subject": "EP250827b: Swift observations of AT 2025wkm",
"createdOn": 1756760251338,
"submitter": "xjh@andrew.cmu.edu",
"circularId": 41641,
"submittedHow": "web"
},
"message_text": "Xander J. Hall (Carnegie Mellon U.), Tomas Ahumada (Caltech), and Robert Stein (UMD) on behalf of the ZTF collaboration:\n\nWe requested Swift ToO observations of the X-ray flare EP250827b and optical transient AT 2025wkm reported by Schroeder et al. (GCN 41635).\n\nThe observation was taken with a midpoint time of 2025-08-31 at 21:13:29 UT, approximately 4.62 days after the flare, with a duration of 4ks.\n\nThe source was not detected with XRT with an upper limit of 2.5 * 10^-3 cts/s at 0.3 - 10 keV. Given the redshift reported by Sevilla & Ho (GCN 41639) of z = 0.1200 this gives a rough luminosity upper limit of 4.5 * 10^42 erg/s. \n\nWe clearly detect a source at the position of AT 2025wkm in UVOT observations. We use a synthetic galaxy model to produce subtracted magnitudes and correct for galactic extinction. We report in the UVW1 filter, a magnitude of m= 21.7 +/- 0.4 AB and in the UVM2 filter, a magnitude of m = 22.2 +/- 0.3.\n\nWe thank the Swift team, Observatory Duty Scientists and the PI for promptly scheduling and making these observations possible.\n",
"published": "2025-09-01T20:57:37.331704Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-01T20:57:37.331721Z",
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"nonlocalizedevents": [],
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},
{
"id": 5778977,
"topic": "gcn.circulars",
"uuid": "dd7bbf10-88cb-426e-a634-31852e62a2ea",
"title": "EP250827b: VLA Observations",
"submitter": "Genevieve Schroeder at Cornell University <genevieveschroeder@u.northwestern.edu>",
"authors": "Genevieve Schroeder at Cornell University <genevieveschroeder@u.northwestern.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41838"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250827b",
"subject": "EP250827b: VLA Observations",
"createdOn": 1758029235641,
"submitter": "Genevieve Schroeder at Cornell University <genevieveschroeder@u.northwestern.edu>",
"circularId": 41838,
"submittedHow": "web"
},
"message_text": "G. Schroeder (Cornell), D. A. Perley (LJMU), X. J. Hall (CMU), A. Y. Q. Ho (Cornell), Gokul Srinivasaragavan (UMD) report:\n\nWe observed the location of the optical transient AT2025wkm, associated with EP250827b (Schroeder et al., GCN 41635) with the NSF’s Karl G. Jansky Very Large Array under program 25B-363 (PI Perley) on 2025 September 13 at a mid time of 13:02 UT (~17.3 days post discovery) at a mid frequency of 10 GHz (4 GHz bandwidth). \n\nBased on preliminary analysis, we detect a ~6 sigma source with a flux density of ~28 microJy. At a redshift of z = 0.120 (Sevilla et al., GCN 41639), this corresponds to a luminosity of ~1e28 erg/s/Hz. This is a factor of ~6 less luminous than the radio emission associated with SN1998bw (Kulkarni et al. Nature, 395, 663), and a factor of ~5 more luminous than the radio emission associated with SN2006aj (Soderberg et al. 2006, Nature, 442, 1014) at a similar observing frequency and epoch. If the radio emission can be attributed solely to star formation, this would indicate a radio star formation rate of ~3 Msol/year. Additional followup is planned to determine variability of the source.\n\nWe thank the VLA staff for quickly approving and executing these observations.",
"published": "2025-09-16T13:27:24.743489Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-16T13:27:24.743515Z",
"modified": "2025-09-16T13:27:24.749897Z",
"nonlocalizedevents": [],
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},
{
"id": 5781007,
"topic": "gcn.circulars",
"uuid": "7859c27b-8c5c-482e-be5e-358917f33be9",
"title": "EP250827b: VLA Observations",
"submitter": "Genevieve Schroeder at Cornell University <genevieveschroeder@u.northwestern.edu>",
"authors": "Genevieve Schroeder at Cornell University <genevieveschroeder@u.northwestern.edu>",
"data": {
"urls": {
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},
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"bibcode": "2025GCN.41838....1S",
"eventId": "EP250827b",
"subject": "EP250827b: VLA Observations",
"createdOn": 1758029235641,
"submitter": "Genevieve Schroeder at Cornell University <genevieveschroeder@u.northwestern.edu>",
"circularId": 41838,
"submittedHow": "web"
},
"message_text": "G. Schroeder (Cornell), D. A. Perley (LJMU), X. J. Hall (CMU), A. Y. Q. Ho (Cornell), Gokul Srinivasaragavan (UMD) report:\n\nWe observed the location of the optical transient AT2025wkm, associated with EP250827b (Schroeder et al., GCN 41635) with the NSF’s Karl G. Jansky Very Large Array under program 25B-363 (PI Perley) on 2025 September 13 at a mid time of 13:02 UT (~17.3 days post discovery) at a mid frequency of 10 GHz (4 GHz bandwidth). \n\nBased on preliminary analysis, we detect a ~6 sigma source with a flux density of ~28 microJy. At a redshift of z = 0.120 (Sevilla et al., GCN 41639), this corresponds to a luminosity of ~1e28 erg/s/Hz. This is a factor of ~6 less luminous than the radio emission associated with SN1998bw (Kulkarni et al. Nature, 395, 663), and a factor of ~5 more luminous than the radio emission associated with SN2006aj (Soderberg et al. 2006, Nature, 442, 1014) at a similar observing frequency and epoch. If the radio emission can be attributed solely to star formation, this would indicate a radio star formation rate of ~3 Msol/year. Additional followup is planned to determine variability of the source.\n\nWe thank the VLA staff for quickly approving and executing these observations.",
"published": "2025-09-22T08:08:50.090879Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:50.090887Z",
"modified": "2025-09-22T08:08:50.094759Z",
"nonlocalizedevents": [],
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},
{
"id": 5780979,
"topic": "gcn.circulars",
"uuid": "93c02695-17fe-4de9-a9cb-ae47a30318bf",
"title": "EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope",
"submitter": "kde1@mit.edu",
"authors": "kde1@mit.edu",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41652"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41652....1D",
"eventId": "EP250828a",
"subject": "EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope",
"createdOn": 1756787981514,
"submitter": "kde1@mit.edu",
"circularId": 41652,
"submittedHow": "web"
},
"message_text": "K. De (Columbia/CCA), S. Ibrahim (Columbia), T. Suen (Columbia), M. Sitaram (Columbia), D. Schiminovich (Columbia), G. Mo (Caltech/Carnegie), K. Shin (Caltech)\n\nWe observed the field of the X-ray transient EP250828a (Liu et al., GCN 41574; Aryan et al., GCN 41579; Taguchi et al., GCN 41582; Yao et al., GCN 41583; Fu et al., GCN 41584; Zheng et al., GCN 41586; Lipunov et al., GCN 41588; Bochenek et al., GCN 41590; Aryan et al., GCN 41591; Ni et al., GCN 41592) during commissioning operations of the MDM InfraRed Astronomy inGaas Explorer (MIRAGE) instrument on the MDM 1.3m telescope. Observations were carried out starting at UTC 2025-08-28 10:59:08, starting ~ 3.4 hours after the time of the X-ray detection. \n\nWe obtained a series of dithered exposures in Y-band amounting to a total exposure time of 850 s. Images were aligned, stacked and calibrated to the PS1 catalog. Performing forced photometry at the position of the X-ray and optical counterpart reported in GCN 41582, 41583, 41591, 41592, we do not detect a point source to a 5 sigma limiting magnitude of > 19.1 AB mag. Analysis will be improved as further commissioning data is processed. \n\nMIRAGE is a new YJH-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the commissioning observations.",
"published": "2025-09-22T08:08:49.800865Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-22T08:08:49.800873Z",
"modified": "2025-09-22T08:08:49.804276Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5774682,
"topic": "gcn.circulars",
"uuid": "d955b00d-6ce4-4d45-9190-64dc563ed588",
"title": "EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope",
"submitter": "kde1@mit.edu",
"authors": "kde1@mit.edu",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41652"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250828a",
"subject": "EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope",
"createdOn": 1756787981514,
"submitter": "kde1@mit.edu",
"circularId": 41652,
"submittedHow": "web"
},
"message_text": "K. De (Columbia/CCA), S. Ibrahim (Columbia), T. Suen (Columbia), M. Sitaram (Columbia), D. Schiminovich (Columbia), G. Mo (Caltech/Carnegie), K. Shin (Caltech)\n\nWe observed the field of the X-ray transient EP250828a (Liu et al., GCN 41574; Aryan et al., GCN 41579; Taguchi et al., GCN 41582; Yao et al., GCN 41583; Fu et al., GCN 41584; Zheng et al., GCN 41586; Lipunov et al., GCN 41588; Bochenek et al., GCN 41590; Aryan et al., GCN 41591; Ni et al., GCN 41592) during commissioning operations of the MDM InfraRed Astronomy inGaas Explorer (MIRAGE) instrument on the MDM 1.3m telescope. Observations were carried out starting at UTC 2025-08-28 10:59:08, starting ~ 3.4 hours after the time of the X-ray detection. \n\nWe obtained a series of dithered exposures in Y-band amounting to a total exposure time of 850 s. Images were aligned, stacked and calibrated to the PS1 catalog. Performing forced photometry at the position of the X-ray and optical counterpart reported in GCN 41582, 41583, 41591, 41592, we do not detect a point source to a 5 sigma limiting magnitude of > 19.1 AB mag. Analysis will be improved as further commissioning data is processed. \n\nMIRAGE is a new YJH-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the commissioning observations.",
"published": "2025-09-02T04:39:50.469305Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-02T04:39:50.469321Z",
"modified": "2025-09-02T04:39:50.483546Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776684,
"topic": "gcn.circulars",
"uuid": "8f56e33f-5624-44d0-bfed-727f5b18a59f",
"title": "EP250828a: Einstein Probe detection of an X-ray transient",
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"authors": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41574"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41574....1L",
"eventId": "EP250828a",
"subject": "EP250828a: Einstein Probe detection of an X-ray transient",
"createdOn": 1756378262126,
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"circularId": 41574,
"submittedHow": "web"
},
"message_text": "H. Y. Liu (NAO, CAS), K. R. Ni (CCNU) , H. L. Peng (NJNU), Y. J. Song and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team:\n\nWe report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250828a. The transient triggered EP-WXT (ID: 01709200900) at 2025-08-28T07:32:33 (UTC). The WXT position of the source is R.A. = 327.905 deg, DEC = 20.567 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).\n\nA follow-up observation with the Follow-up X-ray Telescope (FXT) was performed at 2025-08-28T08:48:40 (UTC) . Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 327.8966 deg, DEC = 20.5435 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).\n\nFurther information will be updated when the telemetry data is received.\n\nLaunched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).",
"published": "2025-09-08T08:08:48.107542Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:48.107557Z",
"modified": "2025-09-08T08:08:48.111883Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773346,
"topic": "gcn.circulars",
"uuid": "eab0d6dc-ae59-44cf-85fb-0b63f7eb6623",
"title": "EP250828a: Einstein Probe detection of an X-ray transient",
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"authors": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41574"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250828a",
"subject": "EP250828a: Einstein Probe detection of an X-ray transient",
"createdOn": 1756378262126,
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"circularId": 41574,
"submittedHow": "web"
},
"message_text": "H. Y. Liu (NAO, CAS), K. R. Ni (CCNU) , H. L. Peng (NJNU), Y. J. Song and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team:\n\nWe report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250828a. The transient triggered EP-WXT (ID: 01709200900) at 2025-08-28T07:32:33 (UTC). The WXT position of the source is R.A. = 327.905 deg, DEC = 20.567 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).\n\nA follow-up observation with the Follow-up X-ray Telescope (FXT) was performed at 2025-08-28T08:48:40 (UTC) . Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 327.8966 deg, DEC = 20.5435 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).\n\nFurther information will be updated when the telemetry data is received.\n\nLaunched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).",
"published": "2025-08-28T10:51:10.762413Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-28T10:51:10.762429Z",
"modified": "2025-08-28T10:51:10.768411Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776555,
"topic": "gcn.circulars",
"uuid": "cdf52a86-d4a7-45e6-891d-e488ca958fb2",
"title": "EP250828a: Global MASTER-Net observations report",
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"authors": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41588"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41588....1L",
"eventId": "EP250828a",
"subject": "EP250828a: Global MASTER-Net observations report",
"createdOn": 1756457661459,
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"circularId": 41588,
"submittedHow": "email"
},
"message_text": "V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, \nG.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),\nO.Gress, N.Budnev (ISU),\nC.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),\nA. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),\nA.Sosnovskij (CrAO),\nA. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),\nD.Buckley (SAAO),\nR.Rebolo (The Instituto de Astrofisica de Canarias),\nL.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,\nA.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) \n\nMASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250828a ( EP Team et al., GCN 41574) errorbox 75567 sec after notice time and 1 days 1111 sec after trigger time at 2025-08-29 07:51:04 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 76 deg. The sun altitude is -39.8 deg. \n\nThe galactic latitude b = -26 deg., longitude l = 76 deg.\n\n\nReal time updated cover map and OT discovered available here: \nhttps://master.sai.msu.ru/site/master2/observ.php?id=2978651\n\nWe obtain a following upper limits. \n\nTmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment\n_________|_____________________|_____________________|____________________________________|_____|_______|_______|________\n\n 87541 | 2025-08-29 07:51:04 | MASTER-OAFA | (21h 51m 57.17s , +20d 28m 10.2s) | C | 60 | 18.8 | \n 87618 | 2025-08-29 07:52:21 | MASTER-OAFA | (21h 52m 02.14s , +20d 27m 10.6s) | C | 60 | 18.6 | \n 87694 | 2025-08-29 07:53:37 | MASTER-OAFA | (21h 51m 56.69s , +20d 26m 10.1s) | C | 60 | 18.6 | \n 87771 | 2025-08-29 07:54:54 | MASTER-OAFA | (21h 52m 01.95s , +20d 26m 11.4s) | C | 60 | 18.6 | \n 87831 | 2025-08-29 07:54:54 | MASTER-OAFA | (21h 52m 02.01s , +20d 26m 11.0s) | C | 180 | 18.5 | Coadd \n 87844 | 2025-08-29 07:56:07 | MASTER-OAFA | (21h 50m 57.78s , +20d 27m 39.7s) | C | 60 | 18.5 | \n 87918 | 2025-08-29 07:57:20 | MASTER-OAFA | (21h 50m 57.71s , +20d 27m 39.6s) | C | 60 | 18.5 | \n 87991 | 2025-08-29 07:58:34 | MASTER-OAFA | (21h 50m 57.62s , +20d 27m 39.5s) | C | 60 | 18.5 | \n 88064 | 2025-08-29 07:59:46 | MASTER-OAFA | (21h 50m 57.50s , +20d 27m 39.7s) | C | 60 | 18.4 | \n 88137 | 2025-08-29 08:00:59 | MASTER-OAFA | (21h 50m 57.38s , +20d 27m 40.1s) | C | 60 | 18.3 | \n 88723 | 2025-08-29 08:10:46 | MASTER-OAFA | (21h 52m 01.43s , +20d 26m 02.4s) | C | 60 | 17.4 | \n 88801 | 2025-08-29 08:12:04 | MASTER-OAFA | (21h 51m 59.20s , +20d 27m 52.2s) | C | 60 | 17.3 | \n 88879 | 2025-08-29 08:13:22 | MASTER-OAFA | (21h 51m 59.14s , +20d 26m 02.3s) | C | 60 | 17.3 | \n 88939 | 2025-08-29 08:13:22 | MASTER-OAFA | (21h 51m 59.16s , +20d 26m 02.1s) | C | 180 | 17.4 | Coadd \n 88954 | 2025-08-29 08:14:36 | MASTER-OAFA | (21h 52m 02.29s , +20d 27m 53.3s) | C | 60 | 17.0 | \n 89030 | 2025-08-29 08:15:53 | MASTER-OAFA | (21h 51m 56.83s , +20d 26m 54.8s) | C | 60 | 16.6 | \n 89107 | 2025-08-29 08:17:09 | MASTER-OAFA | (21h 51m 55.72s , +20d 27m 52.7s) | C | 60 | 16.0 | \n 89182 | 2025-08-29 08:18:25 | MASTER-OAFA | (21h 52m 01.38s , +20d 26m 50.8s) | C | 60 | 15.7 | \n 89256 | 2025-08-29 08:19:38 | MASTER-OAFA | (21h 51m 55.58s , +20d 25m 48.1s) | C | 60 | 15.1 | \n 89331 | 2025-08-29 08:20:53 | MASTER-OAFA | (21h 52m 01.76s , +20d 26m 13.7s) | C | 60 | 13.9 | \nFilter C is a clear (unfiltred) band. \n\n\nThe observation and reduction will continue. \nThe message may be cited.\n",
"published": "2025-09-08T08:08:41.228300Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:41.228327Z",
"modified": "2025-09-08T08:08:41.233076Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773610,
"topic": "gcn.circulars",
"uuid": "a7392bb2-b205-4155-af38-9da99ffdae7b",
"title": "EP250828a: Global MASTER-Net observations report",
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"authors": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41588"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250828a",
"subject": "EP250828a: Global MASTER-Net observations report",
"createdOn": 1756457661459,
"submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>",
"circularId": 41588,
"submittedHow": "email"
},
"message_text": "V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, \nG.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),\nO.Gress, N.Budnev (ISU),\nC.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),\nA. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),\nA.Sosnovskij (CrAO),\nA. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),\nD.Buckley (SAAO),\nR.Rebolo (The Instituto de Astrofisica de Canarias),\nL.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,\nA.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) \n\nMASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250828a ( EP Team et al., GCN 41574) errorbox 75567 sec after notice time and 1 days 1111 sec after trigger time at 2025-08-29 07:51:04 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 76 deg. The sun altitude is -39.8 deg. \n\nThe galactic latitude b = -26 deg., longitude l = 76 deg.\n\n\nReal time updated cover map and OT discovered available here: \nhttps://master.sai.msu.ru/site/master2/observ.php?id=2978651\n\nWe obtain a following upper limits. \n\nTmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment\n_________|_____________________|_____________________|____________________________________|_____|_______|_______|________\n\n 87541 | 2025-08-29 07:51:04 | MASTER-OAFA | (21h 51m 57.17s , +20d 28m 10.2s) | C | 60 | 18.8 | \n 87618 | 2025-08-29 07:52:21 | MASTER-OAFA | (21h 52m 02.14s , +20d 27m 10.6s) | C | 60 | 18.6 | \n 87694 | 2025-08-29 07:53:37 | MASTER-OAFA | (21h 51m 56.69s , +20d 26m 10.1s) | C | 60 | 18.6 | \n 87771 | 2025-08-29 07:54:54 | MASTER-OAFA | (21h 52m 01.95s , +20d 26m 11.4s) | C | 60 | 18.6 | \n 87831 | 2025-08-29 07:54:54 | MASTER-OAFA | (21h 52m 02.01s , +20d 26m 11.0s) | C | 180 | 18.5 | Coadd \n 87844 | 2025-08-29 07:56:07 | MASTER-OAFA | (21h 50m 57.78s , +20d 27m 39.7s) | C | 60 | 18.5 | \n 87918 | 2025-08-29 07:57:20 | MASTER-OAFA | (21h 50m 57.71s , +20d 27m 39.6s) | C | 60 | 18.5 | \n 87991 | 2025-08-29 07:58:34 | MASTER-OAFA | (21h 50m 57.62s , +20d 27m 39.5s) | C | 60 | 18.5 | \n 88064 | 2025-08-29 07:59:46 | MASTER-OAFA | (21h 50m 57.50s , +20d 27m 39.7s) | C | 60 | 18.4 | \n 88137 | 2025-08-29 08:00:59 | MASTER-OAFA | (21h 50m 57.38s , +20d 27m 40.1s) | C | 60 | 18.3 | \n 88723 | 2025-08-29 08:10:46 | MASTER-OAFA | (21h 52m 01.43s , +20d 26m 02.4s) | C | 60 | 17.4 | \n 88801 | 2025-08-29 08:12:04 | MASTER-OAFA | (21h 51m 59.20s , +20d 27m 52.2s) | C | 60 | 17.3 | \n 88879 | 2025-08-29 08:13:22 | MASTER-OAFA | (21h 51m 59.14s , +20d 26m 02.3s) | C | 60 | 17.3 | \n 88939 | 2025-08-29 08:13:22 | MASTER-OAFA | (21h 51m 59.16s , +20d 26m 02.1s) | C | 180 | 17.4 | Coadd \n 88954 | 2025-08-29 08:14:36 | MASTER-OAFA | (21h 52m 02.29s , +20d 27m 53.3s) | C | 60 | 17.0 | \n 89030 | 2025-08-29 08:15:53 | MASTER-OAFA | (21h 51m 56.83s , +20d 26m 54.8s) | C | 60 | 16.6 | \n 89107 | 2025-08-29 08:17:09 | MASTER-OAFA | (21h 51m 55.72s , +20d 27m 52.7s) | C | 60 | 16.0 | \n 89182 | 2025-08-29 08:18:25 | MASTER-OAFA | (21h 52m 01.38s , +20d 26m 50.8s) | C | 60 | 15.7 | \n 89256 | 2025-08-29 08:19:38 | MASTER-OAFA | (21h 51m 55.58s , +20d 25m 48.1s) | C | 60 | 15.1 | \n 89331 | 2025-08-29 08:20:53 | MASTER-OAFA | (21h 52m 01.76s , +20d 26m 13.7s) | C | 60 | 13.9 | \nFilter C is a clear (unfiltred) band. \n\n\nThe observation and reduction will continue. \nThe message may be cited.\n",
"published": "2025-08-29T08:54:28.150317Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-29T08:54:28.150331Z",
"modified": "2025-08-29T08:54:28.156598Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776817,
"topic": "gcn.circulars",
"uuid": "325ad7e1-6f7b-4469-94eb-85ef8104aa75",
"title": "EP250828a: KAIT optical upper limit",
"submitter": "Weikang Zheng at UC Berkeley <weikang@berkeley.edu>",
"authors": "Weikang Zheng at UC Berkeley <weikang@berkeley.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41586"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41586....1Z",
"eventId": "EP250828a",
"subject": "EP250828a: KAIT optical upper limit",
"createdOn": 1756448196359,
"submitter": "Weikang Zheng at UC Berkeley <weikang@berkeley.edu>",
"circularId": 41586,
"submittedHow": "email"
},
"message_text": "WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and\n\nAlexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:\n\n\nThe 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at\n\nLick Observatory, observed the field of EP250828a (Liu et al.,\n\nGCN 41574) starting at 09:30, Aug 28 UT, about 1.97 hours after\n\nthe burst. A set of clear (roughly R) filter images were obtained.\n\nIn our coadd image, we did not detect the reported afterglow\n\n(Taguchi et al., GCN 41582; Yao et al., GCN 41583; Fu et al., GCN\n\n41584) down to a limiting mag of 20.5 mag (Vega) at a mid-time of\n\n2.67 hours after the burst.\n",
"published": "2025-09-08T08:09:02.937321Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:09:02.937338Z",
"modified": "2025-09-08T08:09:02.942378Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773568,
"topic": "gcn.circulars",
"uuid": "1048feff-66e8-46ff-b4be-826001af2263",
"title": "EP250828a: KAIT optical upper limit",
"submitter": "Weikang Zheng at UC Berkeley <weikang@berkeley.edu>",
"authors": "Weikang Zheng at UC Berkeley <weikang@berkeley.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41586"
},
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250828a",
"subject": "EP250828a: KAIT optical upper limit",
"createdOn": 1756448196359,
"submitter": "Weikang Zheng at UC Berkeley <weikang@berkeley.edu>",
"circularId": 41586,
"submittedHow": "email"
},
"message_text": "WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and\n\nAlexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:\n\n\nThe 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at\n\nLick Observatory, observed the field of EP250828a (Liu et al.,\n\nGCN 41574) starting at 09:30, Aug 28 UT, about 1.97 hours after\n\nthe burst. A set of clear (roughly R) filter images were obtained.\n\nIn our coadd image, we did not detect the reported afterglow\n\n(Taguchi et al., GCN 41582; Yao et al., GCN 41583; Fu et al., GCN\n\n41584) down to a limiting mag of 20.5 mag (Vega) at a mid-time of\n\n2.67 hours after the burst.\n",
"published": "2025-08-29T06:16:44.675236Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-29T06:16:44.675253Z",
"modified": "2025-08-29T06:16:44.681806Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5773617,
"topic": "gcn.circulars",
"uuid": "af4fbd04-5c93-49ca-ad77-58cc88786fab",
"title": "EP250828a: Liverpool Telescope upper limits",
"submitter": "A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>",
"authors": "A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41590"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "EP250828a",
"subject": "EP250828a: Liverpool Telescope upper limits",
"createdOn": 1756459718380,
"submitter": "A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>",
"circularId": 41590,
"submittedHow": "web"
},
"message_text": "A. Bochenek and D. A. Perley (LJMU) report:\n\nWe observed the field of the fast X-ray transient EP250828a (Liu et al., GCN 41574) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x100s exposures in the SDSS r’ and i’ filters starting at 2025-08-29 22:33:53 UT, approximately 15 hours after the trigger.\n \nWe do not detect the reported optical counterpart (Taguchi et al., GCN 41582; Yao et al., GCN 41583) or any new objects within the EP/FXT error region of the transient (Liu et al., GCN 41574). The 3-sigma limiting magnitudes on the stacked images are r > 23.7 mag and i > 23.6 mag. This is consistent with the detection of an optical counterpart candidate by NOT at r ~ 24.4 at 15.2 hours post trigger (Fu et al., GCN 41584).",
"published": "2025-08-29T09:28:47.562543Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-08-29T09:28:47.562557Z",
"modified": "2025-08-29T09:28:47.565940Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776722,
"topic": "gcn.circulars",
"uuid": "cbb6c433-fc7b-4b96-84f9-ba464c2a0593",
"title": "EP250828a: Liverpool Telescope upper limits",
"submitter": "A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>",
"authors": "A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41590"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41590....1B",
"eventId": "EP250828a",
"subject": "EP250828a: Liverpool Telescope upper limits",
"createdOn": 1756459718380,
"submitter": "A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>",
"circularId": 41590,
"submittedHow": "web"
},
"message_text": "A. Bochenek and D. A. Perley (LJMU) report:\n\nWe observed the field of the fast X-ray transient EP250828a (Liu et al., GCN 41574) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x100s exposures in the SDSS r’ and i’ filters starting at 2025-08-29 22:33:53 UT, approximately 15 hours after the trigger.\n \nWe do not detect the reported optical counterpart (Taguchi et al., GCN 41582; Yao et al., GCN 41583) or any new objects within the EP/FXT error region of the transient (Liu et al., GCN 41574). The 3-sigma limiting magnitudes on the stacked images are r > 23.7 mag and i > 23.6 mag. This is consistent with the detection of an optical counterpart candidate by NOT at r ~ 24.4 at 15.2 hours post trigger (Fu et al., GCN 41584).",
"published": "2025-09-08T08:08:49.618533Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:49.618552Z",
"modified": "2025-09-08T08:08:49.622595Z",
"nonlocalizedevents": [],
"targets": []
},
{
"id": 5776595,
"topic": "gcn.circulars",
"uuid": "ac02c856-f1d3-4241-a06f-267466b137e4",
"title": "EP250828a: NOT optical counterpart confirmation",
"submitter": "syfu@nao.cas.cn",
"authors": "syfu@nao.cas.cn",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/41584"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41584....1F",
"eventId": "EP250828a",
"subject": "EP250828a: NOT optical counterpart confirmation",
"createdOn": 1756440042487,
"submitter": "syfu@nao.cas.cn",
"circularId": 41584,
"submittedHow": "web"
},
"message_text": "S.Y. Fu (HUST), J. An, L.B. He, S.Q. Jiang, X. Liu, Z.P. Zhu, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), A. Henderson (NOT) report:\n\nWe observed the field of EP250828a (Liu et al., GCN 41574) using the Nordic Optical Telescope (NOT) located in La Palma (Canary Islands, Spain). Observations were carried out in the r and z filters.\n\nThe previously reported counterpart (candidate) within the EP/FXT error circle by Seimei (Taguchi et al., GCN 41582) and SVOM/VT (Yao et al., GCN 41583) is detected in our stacked r-band image and has decayed to r ~ 24.4 (AB) at a median time of 0.634 day post-trigger, calibrated with PanSTARRS-DR2 and not corrected for Galactic extinction. We thus confirm it is the counterpart of EP2508028a.",
"published": "2025-09-08T08:08:41.768406Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-08T08:08:41.768421Z",
"modified": "2025-09-08T08:08:41.772695Z",
"nonlocalizedevents": [],
"targets": []
}
]
}