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"title": " LIGO/Virgo/KAGRA S251103f: Identification of a GW compact binary merger candidate",
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"subject": " LIGO/Virgo/KAGRA S251103f: Identification of a GW compact binary merger candidate",
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"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe identified the compact binary merger candidate S251103f during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-11-03 22:05:26.540 UTC (GPS time: 1446242744.540). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], PyCBC Live [6], and SPIIR [7] analysis pipelines.\n\nS251103f is an event of interest because its false alarm rate, as estimated by the online analysis, is 4.2e-14 Hz, or about one in 1e6 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S251103f\n\nThe classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%).\n\nAssuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [8] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [8] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%.\n\nThe source chirp mass falls with highest probability in the bin (11.0, 22.0) solar masses, assuming the candidate is astrophysical in origin.\n\nTwo sky maps are available at this time and can be retrieved from the GraceDB event page:\n * amplfi.multiorder.fits,0, an initial localization generated by AMPLFI [9], distributed via GCN and SCiMMA notices about 20 seconds after the candidate event time.\n * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [10], distributed via GCN and SCiMMA notices about 4 minutes after the candidate event time.\n\nThe preferred sky map at this time is bayestar.multiorder.fits,0. For the bayestar.multiorder.fits,0 sky map, the 90% credible region is 981 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2158 +/- 568 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010\n [2] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004\n [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018\n [4] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008\n [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234\n [6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a\n [7] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023\n [8] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [9] Chatterjee et al. MLST 5, 045030 (2024) doi:10.1088/2632-2153/ad8982\n [10] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013\n",
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"title": "LIGO/Virgo/KAGRA S251103f: Updated Sky localization",
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"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S251103f (GCN Circular 42564). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:\n\nhttps://gracedb.ligo.org/superevents/S251103f\n\nFor the Bilby.multiorder.fits,0 sky map, the 90% credible region is 757 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2158 +/- 537 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040",
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"title": " LIGO/Virgo/KAGRA S251103f: Identification of a GW compact binary merger candidate",
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{
"id": 5800211,
"topic": "gcn.circulars",
"uuid": "139143ac-260d-4b59-8af1-6755962d803d",
"title": "LIGO/Virgo/KAGRA S251108dn: Updated Sky localization",
"submitter": "Abhishek Sharma at IIT Gandhinagar <abhishek.sharma@ligo.org>",
"authors": "Abhishek Sharma at IIT Gandhinagar <abhishek.sharma@ligo.org>",
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},
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"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42627....1L",
"eventId": "LIGO/Virgo/KAGRA S251108dn",
"subject": "LIGO/Virgo/KAGRA S251108dn: Updated Sky localization",
"createdOn": 1762678117587,
"submitter": "Abhishek Sharma at IIT Gandhinagar <abhishek.sharma@ligo.org>",
"circularId": 42627,
"submittedHow": "web"
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"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S251108dn (GCN Circular 42619). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:\n\nhttps://gracedb.ligo.org/superevents/S251108dn\n\nFor the Bilby.multiorder.fits,0 sky map, the 90% credible region is 370 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1089 +/- 246 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040",
"published": "2025-11-17T10:18:31.577323Z",
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{
"id": 5800170,
"topic": "gcn.circulars",
"uuid": "f18f144a-2b93-421c-b985-81188cd316e9",
"title": "LIGO/Virgo/KAGRA S251108dn: Identification of a GW compact binary merger candidate",
"submitter": "FRANCESCO STOLZI at Unisi <stolzi3@unisi.it>",
"authors": "FRANCESCO STOLZI at Unisi <stolzi3@unisi.it>",
"data": {
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},
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"bibcode": "2025GCN.42619....1L",
"eventId": "LIGO/Virgo/KAGRA S251108dn",
"subject": "LIGO/Virgo/KAGRA S251108dn: Identification of a GW compact binary merger candidate",
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"submitter": "FRANCESCO STOLZI at Unisi <stolzi3@unisi.it>",
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},
"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe identified the compact binary merger candidate S251108dn during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-11-08 10:32:43.578 UTC (GPS time: 1446633181.578). The candidate was found by the Aframe [1], cWB BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines.\n\nS251108dn is an event of interest because its false alarm rate, as estimated by the online analysis, is 9.4e-18 Hz, or about one in 1e10 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S251108dn\n\nThe classification of the GW signal, in order of descending probability, is BBH (>99%), NSBH (<1%), Terrestrial (<1%), or BNS (<1%).\n\nNoise transients (glitches) were present in the LIGO Livingston and Virgo detector data within two seconds of the event time, which may affect the parameters or the significance of the candidate.\n\nAssuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [7] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [7] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 2%.\n\nThe source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses, assuming the candidate is astrophysical in origin.\n\nTwo sky maps are available at this time and can be retrieved from the GraceDB event page:\n * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 26 seconds after the candidate event time.\n * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time.\n\nThe preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 697 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1165 +/- 309 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010\n [2] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018\n [3] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008\n [4] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234\n [5] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a\n [6] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023\n [7] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [8] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013\n",
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{
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"title": "LIGO/Virgo/KAGRA S251108dn: Updated Sky localization",
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"authors": "Abhishek Sharma at IIT Gandhinagar <abhishek.sharma@ligo.org>",
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"createdOn": 1762678117587,
"submitter": "Abhishek Sharma at IIT Gandhinagar <abhishek.sharma@ligo.org>",
"circularId": 42627,
"submittedHow": "web"
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"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S251108dn (GCN Circular 42619). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:\n\nhttps://gracedb.ligo.org/superevents/S251108dn\n\nFor the Bilby.multiorder.fits,0 sky map, the 90% credible region is 370 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1089 +/- 246 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040",
"published": "2025-11-09T08:48:44.918289Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-09T08:48:44.918311Z",
"modified": "2025-11-09T08:48:44.928022Z",
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{
"id": 5793841,
"topic": "gcn.circulars",
"uuid": "38173e35-16e4-4ea6-83bc-6c14333d17e9",
"title": "LIGO/Virgo/KAGRA S251108dn: Identification of a GW compact binary merger candidate",
"submitter": "FRANCESCO STOLZI at Unisi <stolzi3@unisi.it>",
"authors": "FRANCESCO STOLZI at Unisi <stolzi3@unisi.it>",
"data": {
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"eventId": "LIGO/Virgo/KAGRA S251108dn",
"subject": "LIGO/Virgo/KAGRA S251108dn: Identification of a GW compact binary merger candidate",
"createdOn": 1762602125875,
"submitter": "FRANCESCO STOLZI at Unisi <stolzi3@unisi.it>",
"circularId": 42619,
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"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe identified the compact binary merger candidate S251108dn during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-11-08 10:32:43.578 UTC (GPS time: 1446633181.578). The candidate was found by the Aframe [1], cWB BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines.\n\nS251108dn is an event of interest because its false alarm rate, as estimated by the online analysis, is 9.4e-18 Hz, or about one in 1e10 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S251108dn\n\nThe classification of the GW signal, in order of descending probability, is BBH (>99%), NSBH (<1%), Terrestrial (<1%), or BNS (<1%).\n\nNoise transients (glitches) were present in the LIGO Livingston and Virgo detector data within two seconds of the event time, which may affect the parameters or the significance of the candidate.\n\nAssuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [7] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [7] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 2%.\n\nThe source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses, assuming the candidate is astrophysical in origin.\n\nTwo sky maps are available at this time and can be retrieved from the GraceDB event page:\n * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 26 seconds after the candidate event time.\n * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time.\n\nThe preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 697 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1165 +/- 309 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010\n [2] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018\n [3] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008\n [4] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234\n [5] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a\n [6] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023\n [7] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [8] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013\n",
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"central_frequency": null
},
"alert_type": "UPDATE",
"sequence_num": 4,
"time_created": "2025-11-09T08:50:15Z",
"superevent_id": "S251108fi",
"external_coinc": null
},
"message_text": "",
"published": "2025-11-09T08:50:16.336247Z",
"message_parser": "IGWN Alert Avro Parser v1",
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"created": "2025-11-09T08:50:16.336271Z",
"modified": "2025-11-09T08:50:16.342512Z"
}
}
],
"references": [
{
"id": 5800226,
"topic": "gcn.circulars",
"uuid": "3d1aec07-76ad-4bef-bd01-714f8dbbdf58",
"title": "LIGO/Virgo/KAGRA S251108fi: Updated Sky localization",
"submitter": "Abhishek Sharma at IIT Gandhinagar <abhishek.sharma@ligo.org>",
"authors": "Abhishek Sharma at IIT Gandhinagar <abhishek.sharma@ligo.org>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42628"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42628....1L",
"eventId": "LIGO/Virgo/KAGRA S251108fi",
"subject": "LIGO/Virgo/KAGRA S251108fi: Updated Sky localization",
"createdOn": 1762678406915,
"submitter": "Abhishek Sharma at IIT Gandhinagar <abhishek.sharma@ligo.org>",
"circularId": 42628,
"submittedHow": "web"
},
"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S251108fi (GCN Circular 42624). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:\n\nhttps://gracedb.ligo.org/superevents/S251108fi\n\nFor the Bilby.multiorder.fits,0 sky map, the 90% credible region is 528 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2972 +/- 957 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040",
"published": "2025-11-17T10:18:31.836466Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:31.836480Z",
"modified": "2025-11-17T10:18:31.841961Z",
"targets": []
},
{
"id": 5800122,
"topic": "gcn.circulars",
"uuid": "cd077128-0d34-45d4-b420-1754998e1f74",
"title": "LIGO/Virgo/KAGRA S251108fi: DDOTI Optical Candidate",
"submitter": "Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx>",
"authors": "Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42632"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42632....1B",
"eventId": "LIGO/Virgo/KAGRA S251108fi",
"subject": "LIGO/Virgo/KAGRA S251108fi: DDOTI Optical Candidate",
"createdOn": 1762759082033,
"submitter": "Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx>",
"circularId": 42632,
"submittedHow": "web"
},
"message_text": "Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report:\n\nWe observe the field of the gravitational wave candidate S251108fi (LVKC, GCN Circ. 42624) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-11-10 UTC.\n\nDDOTI observed from 02:22 UTC to 04:35 UTC (T+31.4 h to T+33.6 h after the trigger), with a total exposure time of 72 minutes, pointing the region reported by the IceCube Collaboration (GCN Circ. 42630).\n\nComparing our observations with the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we identify an uncatalogued source at:\n\nRA = 00:57:11.36 (14.2973 d)\nDEC= +07:39:07.1 (7.6520 d)\n\nwith a preliminary magnitude AB magnitude of:\n\nw = 20.11 +/- 0.11.\n\nThis source lies outside the IceCube region but within the 90% credible region reported by the LVK Collaboration (GCN Circ. 42628). It is located approximately 4\" from a known galaxy with a photometric redshift of z = 0.214 ± 0.031 in the Legacy Survey DR10 (Dey et al. 2019). If they are associated, such a redshift would make a connection with the GW candidate unlikely.\n\nHowever, further observations and analysis are ongoing.\n\nThis value is not corrected for the Galactic extinction.\n\nWe thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir.",
"published": "2025-11-17T10:18:30.372218Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:30.372234Z",
"modified": "2025-11-17T10:18:30.377676Z",
"targets": []
},
{
"id": 5800121,
"topic": "gcn.circulars",
"uuid": "7a373672-f763-4ed8-9f4d-c1a3a99892d0",
"title": "LIGO/Virgo/KAGRA S251108fi: Identification of a GW compact binary merger candidate",
"submitter": "joshua.freed@ligo.org",
"authors": "joshua.freed@ligo.org",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42624"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42624....1L",
"eventId": "LIGO/Virgo/KAGRA S251108fi",
"subject": "LIGO/Virgo/KAGRA S251108fi: Identification of a GW compact binary merger candidate",
"createdOn": 1762631125038,
"submitter": "joshua.freed@ligo.org",
"circularId": 42624,
"submittedHow": "web"
},
"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe identified the compact binary merger candidate S251108fi during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-11-08 19:13:28.506 UTC (GPS time: 1446664426.506). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], and PyCBC Live [6] analysis pipelines.\n\nS251108fi is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.3e-12 Hz, or about one in 1e4 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S251108fi\n\nThe classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%).\n\nAssuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [7] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [7] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%.\n\nThe source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin.\n\nTwo sky maps are available at this time and can be retrieved from the GraceDB event page:\n * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 25 seconds after the candidate event time.\n * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 4 minutes after the candidate event time.\n\nThe preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 1524 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3537 +/- 1032 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010\n [2] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004\n [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018\n [4] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008\n [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234\n [6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a\n [7] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [8] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013\n\n",
"published": "2025-11-17T10:18:30.347553Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:30.347568Z",
"modified": "2025-11-17T10:18:30.352999Z",
"targets": []
},
{
"id": 5800080,
"topic": "gcn.circulars",
"uuid": "1b2a6103-26f1-4a1c-a99c-b878f87face5",
"title": "LIGO/Virgo/KAGRA S251108fi: One counterpart neutrino candidate from IceCube neutrino searches",
"submitter": "Alicia Mand at IceCube/UW-Madison <aemand@wisc.edu>",
"authors": "Alicia Mand at IceCube/UW-Madison <aemand@wisc.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42630"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42630....1I",
"eventId": "LIGO/Virgo/KAGRA S251108fi",
"subject": "LIGO/Virgo/KAGRA S251108fi: One counterpart neutrino candidate from IceCube neutrino searches",
"createdOn": 1762728126619,
"submitter": "Alicia Mand at IceCube/UW-Madison <aemand@wisc.edu>",
"circularId": 42630,
"submittedHow": "web"
},
"message_text": "IceCube Collaboration (http://icecube.wisc.edu/) reports:\n\nSearches for track-like muon neutrino events detected by IceCube consistent with the sky localization of gravitational-wave candidate S251108fi (GCN 42628) in a time range of 1000 seconds centered on the alert event time (2025-11-08 19:05:08.506 UTC to 2025-11-08 19:21:48.506 UTC) have been performed [1,2]. During this time period IceCube was collecting good quality data. Two hypothesis tests were conducted. The first search is a maximum likelihood analysis which searches for a generic point-like neutrino source coincident with the given GW skymap. The second uses a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors, such as GW source distance, in the significance estimate [3].\n\nOne track-like event is found in spatial and temporal coincidence with the gravitational-wave candidate S251108fi calculated from the map circulated in the 4-Update notice. This represents an overall p-value of 0.0076 from the generic transient search and an overall p-value of 0.0421 for the Bayesian search. These p-values measure the consistency of the observed track-like events with the known atmospheric backgrounds for this single map (not trials corrected for multiple GW events). The most probable multi-messenger source direction based on the neutrinos and GW skymap is RA 15.12, Dec 9.06 degrees.\n\nThe reported p-values can differ due to the estimated distance of the GW candidate. The distance is used as a prior in the Bayesian binary merger search, while it is not taken into account in the generic transient point-like source search. The false alarm rate of these coincidences can be obtained by multiplying the p-values with their corresponding GW trigger rates. Further details are available at https://gcn.nasa.gov/missions/icecube. Additional details and updates will be posted at https://roc.icecube.wisc.edu/public/LvkNuTrackSearch/.\n\nProperties of the coincident event are shown below.\n\n| dt(s) | RA(deg) | Dec(deg) | Angular uncertainty(deg)| p-value(generic transient)| p-value(Bayesian) |\n|-------|----------|----------|-------------------------|---------------------------|-----------------------|\n|-242.48 | 15.01 | 9.06 | 1.13 | 0.0076 | 0.0421 |\n\nwhere:\ndt = Time of track event minus time of GW trigger (sec).\nAngular uncertainty = Angular uncertainty of track event: the radius of a circle \n representing 90% CL containment by area.\np-value = the p-value for this specific track event from each search. \n Event p-values are provided when the per-event p-value is less than 0.1 in either search.\n\nThe IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu\n\n\n[1] M. G. Aartsen et al 2020 ApJL 898 L10\n[2] Abbasi et al. Astrophys.J. 944 (2023) 1, 80\n[3] I. Bartos et al. 2019 Phys. Rev. D 100, 083017\n",
"published": "2025-11-17T10:18:29.640831Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:29.640844Z",
"modified": "2025-11-17T10:18:29.646593Z",
"targets": []
},
{
"id": 5794271,
"topic": "gcn.circulars",
"uuid": "47f55f49-d15c-4a3b-b79f-e1ab9161deff",
"title": "LIGO/Virgo/KAGRA S251108fi: DDOTI Optical Candidate",
"submitter": "Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx>",
"authors": "Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42632"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251108fi",
"subject": "LIGO/Virgo/KAGRA S251108fi: DDOTI Optical Candidate",
"createdOn": 1762759082033,
"submitter": "Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx>",
"circularId": 42632,
"submittedHow": "web"
},
"message_text": "Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report:\n\nWe observe the field of the gravitational wave candidate S251108fi (LVKC, GCN Circ. 42624) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-11-10 UTC.\n\nDDOTI observed from 02:22 UTC to 04:35 UTC (T+31.4 h to T+33.6 h after the trigger), with a total exposure time of 72 minutes, pointing the region reported by the IceCube Collaboration (GCN Circ. 42630).\n\nComparing our observations with the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we identify an uncatalogued source at:\n\nRA = 00:57:11.36 (14.2973 d)\nDEC= +07:39:07.1 (7.6520 d)\n\nwith a preliminary magnitude AB magnitude of:\n\nw = 20.11 +/- 0.11.\n\nThis source lies outside the IceCube region but within the 90% credible region reported by the LVK Collaboration (GCN Circ. 42628). It is located approximately 4\" from a known galaxy with a photometric redshift of z = 0.214 ± 0.031 in the Legacy Survey DR10 (Dey et al. 2019). If they are associated, such a redshift would make a connection with the GW candidate unlikely.\n\nHowever, further observations and analysis are ongoing.\n\nThis value is not corrected for the Galactic extinction.\n\nWe thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir.",
"published": "2025-11-10T07:18:09.480767Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-10T07:18:09.480788Z",
"modified": "2025-11-10T07:18:09.489989Z",
"targets": []
},
{
"id": 5794170,
"topic": "gcn.circulars",
"uuid": "3bb0c292-ffc9-49cf-9058-d1dfa5fb5448",
"title": "LIGO/Virgo/KAGRA S251108fi: One counterpart neutrino candidate from IceCube neutrino searches",
"submitter": "Alicia Mand at IceCube/UW-Madison <aemand@wisc.edu>",
"authors": "Alicia Mand at IceCube/UW-Madison <aemand@wisc.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42630"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251108fi",
"subject": "LIGO/Virgo/KAGRA S251108fi: One counterpart neutrino candidate from IceCube neutrino searches",
"createdOn": 1762728126619,
"submitter": "Alicia Mand at IceCube/UW-Madison <aemand@wisc.edu>",
"circularId": 42630,
"submittedHow": "web"
},
"message_text": "IceCube Collaboration (http://icecube.wisc.edu/) reports:\n\nSearches for track-like muon neutrino events detected by IceCube consistent with the sky localization of gravitational-wave candidate S251108fi (GCN 42628) in a time range of 1000 seconds centered on the alert event time (2025-11-08 19:05:08.506 UTC to 2025-11-08 19:21:48.506 UTC) have been performed [1,2]. During this time period IceCube was collecting good quality data. Two hypothesis tests were conducted. The first search is a maximum likelihood analysis which searches for a generic point-like neutrino source coincident with the given GW skymap. The second uses a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors, such as GW source distance, in the significance estimate [3].\n\nOne track-like event is found in spatial and temporal coincidence with the gravitational-wave candidate S251108fi calculated from the map circulated in the 4-Update notice. This represents an overall p-value of 0.0076 from the generic transient search and an overall p-value of 0.0421 for the Bayesian search. These p-values measure the consistency of the observed track-like events with the known atmospheric backgrounds for this single map (not trials corrected for multiple GW events). The most probable multi-messenger source direction based on the neutrinos and GW skymap is RA 15.12, Dec 9.06 degrees.\n\nThe reported p-values can differ due to the estimated distance of the GW candidate. The distance is used as a prior in the Bayesian binary merger search, while it is not taken into account in the generic transient point-like source search. The false alarm rate of these coincidences can be obtained by multiplying the p-values with their corresponding GW trigger rates. Further details are available at https://gcn.nasa.gov/missions/icecube. Additional details and updates will be posted at https://roc.icecube.wisc.edu/public/LvkNuTrackSearch/.\n\nProperties of the coincident event are shown below.\n\n| dt(s) | RA(deg) | Dec(deg) | Angular uncertainty(deg)| p-value(generic transient)| p-value(Bayesian) |\n|-------|----------|----------|-------------------------|---------------------------|-----------------------|\n|-242.48 | 15.01 | 9.06 | 1.13 | 0.0076 | 0.0421 |\n\nwhere:\ndt = Time of track event minus time of GW trigger (sec).\nAngular uncertainty = Angular uncertainty of track event: the radius of a circle \n representing 90% CL containment by area.\np-value = the p-value for this specific track event from each search. \n Event p-values are provided when the per-event p-value is less than 0.1 in either search.\n\nThe IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu\n\n\n[1] M. G. Aartsen et al 2020 ApJL 898 L10\n[2] Abbasi et al. Astrophys.J. 944 (2023) 1, 80\n[3] I. Bartos et al. 2019 Phys. Rev. D 100, 083017\n",
"published": "2025-11-09T22:42:15.678519Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-09T22:42:15.678542Z",
"modified": "2025-11-09T22:42:15.699615Z",
"targets": []
},
{
"id": 5794056,
"topic": "gcn.circulars",
"uuid": "32995fca-8c88-4a7a-8fb8-551ad63bef4d",
"title": "LIGO/Virgo/KAGRA S251108fi: Updated Sky localization",
"submitter": "Abhishek Sharma at IIT Gandhinagar <abhishek.sharma@ligo.org>",
"authors": "Abhishek Sharma at IIT Gandhinagar <abhishek.sharma@ligo.org>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42628"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251108fi",
"subject": "LIGO/Virgo/KAGRA S251108fi: Updated Sky localization",
"createdOn": 1762678406915,
"submitter": "Abhishek Sharma at IIT Gandhinagar <abhishek.sharma@ligo.org>",
"circularId": 42628,
"submittedHow": "web"
},
"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S251108fi (GCN Circular 42624). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:\n\nhttps://gracedb.ligo.org/superevents/S251108fi\n\nFor the Bilby.multiorder.fits,0 sky map, the 90% credible region is 528 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2972 +/- 957 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040",
"published": "2025-11-09T08:53:27.950327Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-09T08:53:27.950348Z",
"modified": "2025-11-09T08:53:27.956219Z",
"targets": []
},
{
"id": 5793922,
"topic": "gcn.circulars",
"uuid": "ab3a03d5-30f1-4eeb-b99b-1ea25e941255",
"title": "LIGO/Virgo/KAGRA S251108fi: Identification of a GW compact binary merger candidate",
"submitter": "joshua.freed@ligo.org",
"authors": "joshua.freed@ligo.org",
"data": {
"urls": {
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},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251108fi",
"subject": "LIGO/Virgo/KAGRA S251108fi: Identification of a GW compact binary merger candidate",
"createdOn": 1762631125038,
"submitter": "joshua.freed@ligo.org",
"circularId": 42624,
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"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe identified the compact binary merger candidate S251108fi during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-11-08 19:13:28.506 UTC (GPS time: 1446664426.506). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], and PyCBC Live [6] analysis pipelines.\n\nS251108fi is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.3e-12 Hz, or about one in 1e4 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S251108fi\n\nThe classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%).\n\nAssuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [7] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [7] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%.\n\nThe source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin.\n\nTwo sky maps are available at this time and can be retrieved from the GraceDB event page:\n * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 25 seconds after the candidate event time.\n * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 4 minutes after the candidate event time.\n\nThe preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 1524 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3537 +/- 1032 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010\n [2] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004\n [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018\n [4] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008\n [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234\n [6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a\n [7] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [8] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013\n\n",
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{
"id": 5801644,
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"uuid": "fdf06f66-f9f2-4884-aec8-3aef9090cc97",
"title": "LIGO/Virgo/KAGRA S251105aj: SVOM/VT optical observations and preliminary results on SVOM J2320.0-2901",
"submitter": "Yinuo Ma <mayn@bao.ac.cn>",
"authors": "Yinuo Ma <mayn@bao.ac.cn>",
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"message_text": "Y. N. Ma, H. L. Li, L. P. Xin, Z. H. Yao, Y. L. Qiu, C. Wu, 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), H. Yang, O. Godet, J.-L. Atteia, M. Brunet, S. Guillot (IRAP), M. Pillas (IAP) report on behalf of the SVOM/VT team. \n \nSVOM/VT performed a Target of Opportunity observation of the high-energy transient SVOM J2320.0-2901 detected by SVOM/ECLAIRs (Yang et al., GCN 42797), right after S251105aj reported by LIGO/Virgo/KAGRA (The LIGO-Virgo-Kagra Collaboration, GCN 42587; GCN 42616). The observation began at 2025-11-16T00:47:45 UT, 10.5 days after SVOM/ECLAIRs detection, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. \n \nThe VT field of view covered 96% of the 90% C.L. ECLAIRs error region, but no uncataloged sources were detected within the error box of ECL. VT also covered three EP/FXT sources (source#1: RA, Dec = 349.8643, -29.0602 deg; source#2: 350.1419, -29.0148 deg; source#3: 349.9737, -28.8522 deg) reported by Guillot et al. (GCN 42818). None of the known sources became apparent brighter within errorbox of three FXT candidates compared with Legacy Survey DR10. The 3 sigma upper limit was VT_R > 23.6 mag and VT_B > 23.8 mag with the exposure time of 65*70 sec.\n \nFurther analysis is ongoing.\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.",
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"submittedHow": "web"
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"message_text": "S. Guillot, H. Yang, O. Godet, J.-L. Atteia (IRAP), M. Pillas (IAP), L. P. Xin, Y. N. Ma, H. W. Pan, T. Zhao (NAOC), Y. J. Yi, A. Li (BNU), R. X. Hu (WHU), D. Z. Du (ZJU), C. Y. Wang (THU) on behalf of the Einstein Probe (EP) team:\n\nEP-FXT performed a Target of Opportunity observation of the high-energy transient SVOM J2320.0-2901 detected by SVOM/ECLAIRs (Yang et al., GCN 42797), in a search for possible counterparts of the compact binary merger candidate S251105aj (The LIGO-Virgo-Kagra Collaboration, GCN 42587). The observation was conducted at 2025-11-15T21:39:22 UTC with an exposure of 5 ks, about 10.36 days after the GW trigger and the detection time of SVOM J2320.0-2901. EP-FXT covered the full area of the 90% C.L. ECLAIRs error region and detected six sources above a SNR of 4.5 within 15 arcminutes from SVOM J2320.0-2901. Their information is summarized below (RA/Dec in degrees with 10\" error radius (90% C.L.); fluxes are the observed ones in 0.5–10 keV):\n# | Name | RA | Dec | Flux (erg/s/cm^2) | SNR\n—----------------------------------------------------------------------------------------------------\n1 | EPF_J231927.4-290337 | 349.8643 | -29.0602 | 1.4e-13 | 4.7\n2 | EPF_J232034.0-290053 | 350.1419 | -29.0148 | 2.2e-13 | 10.0\n3 | EPF_J231953.7-285108 | 349.9737 | -28.8522 | 1.7e-13 | 5.7\n4 | EPF_J231906.2-290806 | 349.7760 | -29.1351 | 3.4e-13 | 5.8\n5 | EPF_J232051.4-285356 | 350.2140 | -28.8990 | 2.4e-13 | 8.4\n6 | EPF_J232108.1-290032 | 350.2839 | -29.0088 | 2.6e-13 | 7.9\n\nWe cross-matched all six FXT detections against the SIMBAD, NED, and Vizier catalogues, using a 20″ matching radius (for a galaxy at 2000 Mpc, this corresponds to an offset of ~200 kpc). Five FXT detections (#2,3,4,5,6) are matched to five optical quasars correspondingly, with their redshifts in a range of 0.721 to 1.641, higher than z=0.374 estimated for the GW event. The remaining source (#1) is matched to a source from the KiDSDR4 QSOs photometric redshifts catalog (Nakoneczny et al., 2021), which is classified as a quasar with 68% probability and a photometric redshift of 0.5 +/- 1.2 based on machine learning estimates. \nWe conducted SVOM/VT on this field with the results reported in GCN 42819. \n\nFurther FXT observations of these candidates will be conducted.\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",
"published": "2025-11-24T15:05:57.894943Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-24T15:05:57.894966Z",
"modified": "2025-11-24T15:05:57.900382Z",
"targets": []
},
{
"id": 5801287,
"topic": "gcn.circulars",
"uuid": "17879914-ca00-4b73-b687-0917052e4a09",
"title": "LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient SVOM J2320.0-2901 through targeted search",
"submitter": "SVOM_group <svomgroup@bao.ac.cn>",
"authors": "SVOM_group <svomgroup@bao.ac.cn>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42797"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251105aj",
"subject": "LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient SVOM J2320.0-2901 through targeted search",
"version": 2,
"editedBy": "Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>",
"editedOn": 1763845732059,
"createdOn": 1763805614820,
"submitter": "SVOM_group <svomgroup@bao.ac.cn>",
"circularId": 42797,
"submittedHow": "web"
},
"message_text": "H. Yang, O. Godet, J.-L. Atteia, M. Brunet, S. Guillot (IRAP), M. Pillas (IAP), L. P. Xin, Y. N. Ma (NAOC)\n\nUsing the event-by-event data downloaded through the X-band ground stations, we report on the identification of a faint SVOM/ECLAIRs transient SVOM J2320.0-2901 detected at 2025-11-05T13:00:48.34 UTC (T0), 88.4 s after the compact binary merger candidate S251105aj (The LIGO-Virgo-Kagra Collaboration, GCN 42587). This transient was detected through an offline targeted search for possible counterparts of the GW event S251105aj. \n\nSVOM J2320.0-2901 was detected with a timescale of 82 s and below 60 keV, with a best signal-to-noise ratio of 6.1 starting at T0.\n\nThe localization of SVOM J2320.0-2901 is RA, Dec = 349.998, -29.022 degrees:\n\nRA (J2000) = 23h20m00s \nDec (J2000) = -29d01m19s\n\nwith a 90% C.L. radius of 13.9 arcmin (including a systematic error of 6 arcmin added in quadrature). This position is about 2 degrees outside the 99% area contour of the Bilby.multiorder.fits skymap of S251105aj. At the time of the GW trigger, ECLAIRs was covering 88% of the skymap 99% area. \n\nThe time-averaged spectrum from T0 to T0+82 s in the energy range of 5-60 keV is well fitted by a blackbody (BB) model, with a measured temperature of 7.8 (+1.5/-1.2) keV. With this model, the total 4-120 keV flux is (3.6+/-0.8)e-9 erg/cm^2/s. Assuming a distance of 2071 Mpc (z=0.374) for the source, this corresponds to a luminosity of 1.8e48 erg/s and a BB emission radius of 1.9e6 cm. \nA broken power-law model is also tested, providing a comparable fit, though with less well-constrained parameters of photon index 1 around -0.5, break energy of 22 (+21/-10) keV, and photon index 2 around 2.9. \n \nAt this stage, the nature of SVOM J2320.0-2901 is unknown. \n\nWe conducted SVOM/VT and EP/FXT follow-up observations on this field. The results will be published in dedicated circulars. \n\nAll the quoted errors are at the 68% confidence level.\n\nThe Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC.\n\nThe SVOM/ECLAIRs point of contact for this source is: Hui Yang (IRAP) (hui.yang@irap.omp.eu) ",
"published": "2025-11-22T21:08:55.482503Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-22T21:08:55.482527Z",
"modified": "2025-11-22T21:08:55.504774Z",
"targets": []
},
{
"id": 5801184,
"topic": "gcn.circulars",
"uuid": "084b3125-8959-4e5b-9a3c-0af2724216f4",
"title": "LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient through targeted search",
"submitter": "SVOM_group <svomgroup@bao.ac.cn>",
"authors": "SVOM_group <svomgroup@bao.ac.cn>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42797"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251105aj",
"subject": "LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient through targeted search",
"createdOn": 1763805614820,
"submitter": "SVOM_group <svomgroup@bao.ac.cn>",
"circularId": 42797,
"submittedHow": "web"
},
"message_text": "H. Yang, O. Godet, J.-L. Atteia, M. Brunet, S. Guillot (IRAP), M. Pillas (IAP), L. P. Xin, Y. N. Ma (NAOC)\n\nUsing the event-by-event data downloaded through the X-band ground stations, we report on the identification of a faint SVOM/ECLAIRs transient detected at 2025-11-05T13:00:48.34 UTC (T0), 88.4 s after the compact binary merger candidate S251105aj (The LIGO-Virgo-Kagra Collaboration, GCN 42587). This transient was detected through an offline targeted search for possible counterparts of the GW event S251105aj. \n\nThe ECLAIRs source was detected with a timescale of 82 s and below 60 keV, with a best signal-to-noise ratio of 6.1 starting at T0.\n\nThe localization of the source is RA, Dec = 349.998, -29.022 degrees:\n\nRA (J2000) = 23h20m00s \nDec (J2000) = -29d01m19s\n\nwith a 90% C.L. radius of 13.9 arcmin (including a systematic error of 6 arcmin added in quadrature). This position is about 2 degrees outside the 99% area contour of the Bilby.multiorder.fits skymap of S251105aj. At the time of the GW trigger, ECLAIRs was covering 88% of the skymap 99% area. \n\nThe time-averaged spectrum from T0 to T0+82 s in the energy range of 5-60 keV is well fitted by a blackbody (BB) model, with a measured temperature of 7.8 (+1.5/-1.2) keV. With this model, the total 4-120 keV flux is (3.6+/-0.8)e-9 erg/cm^2/s. Assuming a distance of 2071 Mpc (z=0.374) for the source, this corresponds to a luminosity of 1.8e48 erg/s and a BB emission radius of 1.9e6 cm. \nA broken power-law model is also tested, providing a comparable fit, though with less well-constrained parameters of photon index 1 around -0.5, break energy of 22 (+21/-10) keV, and photon index 2 around 2.9. \n \nAt this stage, the nature of this transient is unknown. \n\nWe conducted SVOM/VT and EP/FXT follow-up observations on this field. The results will be published in dedicated circulars. \n\nAll the quoted errors are at the 68% confidence level.\n\nThe Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC.\n\nThe SVOM/ECLAIRs point of contact for this source is: Hui Yang (IRAP) (hui.yang@irap.omp.eu) ",
"published": "2025-11-22T10:00:22.934309Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-22T10:00:22.934352Z",
"modified": "2025-11-22T10:00:22.953072Z",
"targets": []
},
{
"id": 5800215,
"topic": "gcn.circulars",
"uuid": "e7c43d00-a54d-41dd-b4e9-e61dbbe13e4f",
"title": "LIGO/Virgo/KAGRA S251105aj: Updated Sky localization",
"submitter": "Lorenzo Pompili at Max Planck Institute for Gravitational Physics <lorenzo.pompili@aei.mpg.de>",
"authors": "Lorenzo Pompili at Max Planck Institute for Gravitational Physics <lorenzo.pompili@aei.mpg.de>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42616"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42616....1L",
"eventId": "LIGO/Virgo/KAGRA S251105aj",
"subject": "LIGO/Virgo/KAGRA S251105aj: Updated Sky localization",
"createdOn": 1762536184034,
"submitter": "Lorenzo Pompili at Max Planck Institute for Gravitational Physics <lorenzo.pompili@aei.mpg.de>",
"circularId": 42616,
"submittedHow": "web"
},
"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S251105aj (GCN Circular 42587). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:\n\nhttps://gracedb.ligo.org/superevents/S251105aj\n\nFor the Bilby.multiorder.fits,0 sky map, the 90% credible region is 376 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2483 +/- 735 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040",
"published": "2025-11-17T10:18:31.651083Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:31.651097Z",
"modified": "2025-11-17T10:18:31.656771Z",
"targets": []
},
{
"id": 5800118,
"topic": "gcn.circulars",
"uuid": "94774e18-7e1d-4790-bc4a-30d126a4b3a6",
"title": "LIGO/Virgo/KAGRA S251105aj: Identification of a GW compact binary merger candidate",
"submitter": "Jeremias Sobrinho <jeremiasbezerra.sobrinho@ligo.org>",
"authors": "Jeremias Sobrinho <jeremiasbezerra.sobrinho@ligo.org>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42587"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42587....1L",
"eventId": "LIGO/Virgo/KAGRA S251105aj",
"subject": "LIGO/Virgo/KAGRA S251105aj: Identification of a GW compact binary merger candidate",
"createdOn": 1762350215595,
"submitter": "Jeremias Sobrinho <jeremiasbezerra.sobrinho@ligo.org>",
"circularId": 42587,
"submittedHow": "web"
},
"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe identified the compact binary merger candidate S251105aj during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-11-05 12:59:19.959 UTC (GPS time: 1446382777.959). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], PyCBC Live [6], and SPIIR [7] analysis pipelines.\n\nS251105aj is an event of interest because its false alarm rate, as estimated by the online analysis, is 8e-13 Hz, or about one in 1e5 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S251105aj\n\nThe classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%).\n\nAssuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [8] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [8] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%.\n\nThe source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin.\n\nTwo sky maps are available at this time and can be retrieved from the GraceDB event page:\n * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 27 seconds after the candidate event time.\n * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time.\n\nThe preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 721 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2071 +/- 545 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010\n [2] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004\n [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018\n [4] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008\n [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234\n [6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a\n [7] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023\n [8] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [9] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013\n",
"published": "2025-11-17T10:18:30.296073Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:30.296090Z",
"modified": "2025-11-17T10:18:30.301858Z",
"targets": []
},
{
"id": 5793306,
"topic": "gcn.circulars",
"uuid": "080ea8b7-bc96-4b4f-84db-988cdbf84224",
"title": "LIGO/Virgo/KAGRA S251105aj: Identification of a GW compact binary merger candidate",
"submitter": "Jeremias Sobrinho <jeremiasbezerra.sobrinho@ligo.org>",
"authors": "Jeremias Sobrinho <jeremiasbezerra.sobrinho@ligo.org>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42587"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251105aj",
"subject": "LIGO/Virgo/KAGRA S251105aj: Identification of a GW compact binary merger candidate",
"createdOn": 1762350215595,
"submitter": "Jeremias Sobrinho <jeremiasbezerra.sobrinho@ligo.org>",
"circularId": 42587,
"submittedHow": "web"
},
"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe identified the compact binary merger candidate S251105aj during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-11-05 12:59:19.959 UTC (GPS time: 1446382777.959). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], PyCBC Live [6], and SPIIR [7] analysis pipelines.\n\nS251105aj is an event of interest because its false alarm rate, as estimated by the online analysis, is 8e-13 Hz, or about one in 1e5 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S251105aj\n\nThe classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%).\n\nAssuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [8] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [8] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%.\n\nThe source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin.\n\nTwo sky maps are available at this time and can be retrieved from the GraceDB event page:\n * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 27 seconds after the candidate event time.\n * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time.\n\nThe preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 721 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2071 +/- 545 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010\n [2] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004\n [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018\n [4] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008\n [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234\n [6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a\n [7] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023\n [8] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [9] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013\n",
"published": "2025-11-05T13:43:42.959414Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-05T13:43:42.959441Z",
"modified": "2025-11-05T13:43:42.966457Z",
"targets": []
}
]
},
{
"event_id": "S251112cm",
"sequences": [
{
"id": 11086,
"sequence_number": 1,
"sequence_type": "PRELIMINARY",
"message": {
"id": 5795135,
"topic": "igwn.gwalert",
"uuid": "287b6f41-467a-4fe8-b009-9c50dbe18b18",
"title": "S251112cm - PRELIMINARY",
"submitter": "cody.messick-30d512c8",
"authors": "LVK",
"data": {
"urls": {
"skymap": "https://gracedb.ligo.org/api/superevents/S251112cm/files/bayestar.multiorder.fits,0",
"gracedb": "https://gracedb.ligo.org/superevents/S251112cm/view/"
},
"event": {
"far": 5.102904e-09,
"time": "2025-11-12T15:18:45.362Z",
"group": "CBC",
"search": "SSM",
"area_50": 368.8695570703079,
"area_90": 1219.703489903128,
"duration": null,
"pipeline": "MBTA",
"properties": {
"HasNS": 0.08,
"HasSSM": 1.0,
"HasMassGap": 0.0
},
"instruments": [
"H1",
"L1",
"V1"
],
"significant": true,
"skymap_hash": "0e3f3a92d6b3a64e58a1542aa6aba6db",
"classification": {},
"skymap_version": 0,
"central_frequency": null
},
"alert_type": "PRELIMINARY",
"sequence_num": 1,
"time_created": "2025-11-12T15:19:43Z",
"superevent_id": "S251112cm",
"external_coinc": null
},
"message_text": "",
"published": "2025-11-12T15:19:45.416484Z",
"message_parser": "IGWN Alert Avro Parser v1",
"retracted": false,
"created": "2025-11-12T15:19:45.416510Z",
"modified": "2025-11-12T15:19:45.504012Z"
}
},
{
"id": 11087,
"sequence_number": 2,
"sequence_type": "PRELIMINARY",
"message": {
"id": 5795136,
"topic": "igwn.gwalert",
"uuid": "a6984168-a1af-4bc1-97f0-5c3482664b37",
"title": "S251112cm - PRELIMINARY",
"submitter": "cody.messick-30d512c8",
"authors": "LVK",
"data": {
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}
},
{
"id": 11088,
"sequence_number": 3,
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"message": {
"id": 5795139,
"topic": "igwn.gwalert",
"uuid": "d66aef35-0e19-45ee-b1a0-aa35bd737594",
"title": "S251112cm - INITIAL",
"submitter": "cody.messick-30d512c8",
"authors": "LVK",
"data": {
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"time_created": "2025-11-12T15:44:10Z",
"superevent_id": "S251112cm",
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},
"message_text": "",
"published": "2025-11-12T15:44:11.260368Z",
"message_parser": "IGWN Alert Avro Parser v1",
"retracted": false,
"created": "2025-11-12T15:44:11.260395Z",
"modified": "2025-11-12T15:44:11.280008Z"
}
},
{
"id": 11104,
"sequence_number": 4,
"sequence_type": "UPDATE",
"message": {
"id": 5798139,
"topic": "igwn.gwalert",
"uuid": "8a096d47-57ce-40d0-9f95-12be05a9013a",
"title": "S251112cm - UPDATE",
"submitter": "cody.messick-30d512c8",
"authors": "LVK",
"data": {
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"duration": null,
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"time_created": "2025-11-15T00:30:32Z",
"superevent_id": "S251112cm",
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},
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"published": "2025-11-15T00:30:33.274414Z",
"message_parser": "IGWN Alert Avro Parser v1",
"retracted": false,
"created": "2025-11-15T00:30:33.274447Z",
"modified": "2025-11-15T00:30:33.290799Z"
}
}
],
"references": [
{
"id": 5802493,
"topic": "gcn.circulars",
"uuid": "927269af-1e90-472d-aff5-ab47cd5d88ec",
"title": "LIGO/Virgo/KAGRA S251112cm: GECKO/KMTNet tiling observations and transient candidates",
"submitter": "Mankeun Jeong <jmk5040@gmail.com>",
"authors": "Mankeun Jeong <jmk5040@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42867"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: GECKO/KMTNet tiling observations and transient candidates",
"createdOn": 1764317718075,
"submitter": "Mankeun Jeong <jmk5040@gmail.com>",
"circularId": 42867,
"submittedHow": "web"
},
"message_text": "Mankeun Jeong, Myungshin Im, Seo-Won Chang, Hyeonho Choi (SNU/SNU ARC), Gregory S.-H. Paek (IfA), and Chung-Uk Lee (KASI), on behalf of the GECKO team\n\nWe observed the S251112cm sky localization region (Updated; GCN 42690) following the LIGO/Virgo/KAGRA trigger. Optical imaging was obtained with the three 1.6-m Korea Microlensing Telescope Network (KMTNet) telescopes at CTIO, SAAO, and SSO, with most of the data taken from SSO.\n\nWe surveyed the southern portion (decl. < -10 deg) of the S251112cm 90% localization region, covering ~1,012 deg^2 from 2025-11-13 to 2025-11-27. During the first three nights, we obtained R and I imaging with 480 sec total exposure per field (four dithered 120 sec exposures) over ~180 deg^2. For the remainder of the run, observations were conducted in R-band only with the same 480 sec per-field exposure.\n\nA fraction of the surveyed area overlaps with regions having KMTNet Synoptic Survey of the Southern Sky (KS4) reference images. Difference image analysis has been completed for ~60 deg^2, with additional processing ongoing.\n\nBelow we list transient candidates re-identified from TNS and new GECKO sources detected in our imaging. Redshifts are adopted from the GLADE+ host-galaxy associations.\n\nName | RA (deg) | Dec (deg) | R (AB mag) | I (AB mag) | Date-Obs (UTC) | Redshift\n-----|----------|-----------|------------|------------|-------------------|---------\nAT2025aebs | 354.16948 | -33.01666 | 20.42 ± 0.05 | 20.66 ± 0.07 | 2025-11-16T12:24:50 | 0.1642\nAT2025adbw | 3.31215 | -36.40843 | 19.07 ± 0.02 | — | 2025-11-14T14:23:37 | —\nAT2025abnc | 7.50565 | -34.96515 | 19.95 ± 0.05 | 20.54 ± 0.08 | 2025-11-14T12:40:10 | 0.1067\nGECKO25dryb | 1.69517 | -33.38614 | 18.95 ± 0.01 | 19.05 ± 0.05 | 2025-11-14T13:39:42 | 0.2094\nGECKO25drxk | 1.53192 | -35.03043 | 18.89 ± 0.01 | 18.86 ± 0.03 | 2025-11-14T13:39:42 | 0.2408\nGECKO25dulp | 358.59508 | -35.91373 | 19.58 ± 0.06 | 18.65 ± 0.03 | 2025-11-16T13:40:59 | 0.0859\nGECKO25dukb | 356.10091 | -34.07094 | 18.37 ± 0.01 | 18.13 ± 0.01 | 2025-11-16T12:24:50 | 0.1269\n\nAll newly identified GECKO candidates lie close to the center of the host galaxy, whose redshifts exceed the estimated distance of S251112cm, indicating they are unrelated to the GW event's physical origin.\n\nFurther difference imaging and transient vetting across the remaining fields are underway.\n\nThe GECKO network (Im et al. 2023; Paek et al. 2024) operates 0.5–1 m class telescopes worldwide for EM follow-up of gravitational-wave events. KMTNet is operated by the Korea Astronomy and Space Science Institute. We thank the KMTNet staff for their support during these observations.",
"published": "2025-11-28T08:15:24.714806Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-28T08:15:24.714829Z",
"modified": "2025-11-28T08:15:24.735430Z",
"targets": []
},
{
"id": 5801665,
"topic": "gcn.circulars",
"uuid": "305e8cdb-28d2-4069-8cfb-b6d3f1db20eb",
"title": "LIGO/Virgo/KAGRA S251112cm: AT 2025adht Kinder follow-up observations",
"submitter": "Janet Chen at National Central University <janetstars@gmail.com>",
"authors": "Janet Chen at National Central University <janetstars@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42825"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: AT 2025adht Kinder follow-up observations",
"createdOn": 1764004951941,
"submitter": "Janet Chen at National Central University <janetstars@gmail.com>",
"circularId": 42825,
"submittedHow": "web"
},
"message_text": "J. H. Gillanders (Oxford), A. Aryan, T.-W. Chen, Y.-H. Lee, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), S. J. Smartt (Oxford), Y. J. Yang (NYUAD), A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, C.-H. Lai, W.-J. Hou, H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: \n\nHere we report follow-up observations of the candidate optical counterpart AT 2025adht (first reported by Franz et al., GCN 42675; see also Anand et al., GCN 42677; Burkhonov et al., GCN 42798) to the LIGO-Virgo-KAGRA (LVK) gravitational-wave event S251112cm (LVK Collaboration, GCN 42650).\n\nWe observed AT 2025adht utilizing the 1m LOT at Lulin Observatory in Taiwan, as part of the Kinder collaboration (Chen & Yang et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations began at 20:31 UTC on November 21, 2025 (MJD 61000.855), 9.225 days after the GW trigger. The second LOT epoch began at 20:16 UTC, or MJD 61001.845, 10.207 days after the GW trigger.\n\nWe utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 images using the 'hotpants' (Becker 2015, ascl.soft. ascl:1504.004) algorithm. \n\nMoreover, we further utilized AutoPhOT to perform PSF photometry. The details of the observations and the measured magnitudes (in the AB system) are as follows:\n\nTelescope | Filter | MJD (start) | t - t0 (d) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass\nLOT | r | 61000.855 | 9.225 | 300 * 6 | 21.83 +/- 0.06 | 1\".2 | 1.41\nLOT | r | 61001.845 | 10.207 | 300 * 6 | 21.86 +/- 0.08 | 1\".2 | 1.46 \n\nBurkhonov et al. (GCN 42698) report a (PS1-equivalent) r-band magnitude of 21.64 +/- 0.1 on MJD 60994.009 (2.37 days post-GW trigger). Our observations indicate that AT 2025adht has faded only slightly in the ~week since detection. The slow evolution indicates that AT 2025adht is not some rapidly declining kilonova-like transient; we instead suspect that AT 2025adht is a background supernova near peak, hence the slow evolution. This interpretation is supported by the Legacy Survey's host galaxy phot-z estimate (0.139 +/- 0.033; see also Anand et al., GCN 42677).\n\nThe presented magnitudes are calibrated using field stars from the ATLAS-RefCat2 catalog from MAST (Tonry et al. 2018, ApJ, 867, 105) and are not corrected for the expected Galactic foreground extinction of A_r = 0.06 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology and details on the capabilities of Lulin observatory telescopes can be found in Aryan et al. 2025, ApJS, 281, 20. doi:10.3847/1538-4365/adfc69.\n\n",
"published": "2025-11-24T17:22:39.079352Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-24T17:22:39.079377Z",
"modified": "2025-11-24T17:22:39.083809Z",
"targets": []
},
{
"id": 5801288,
"topic": "gcn.circulars",
"uuid": "fc39b22d-0c7b-40dd-9d28-7ed97b80b1bd",
"title": "LIGO/Virgo/KAGRA S251112cm: SOAR spectroscopy of three TROVE TNS candidates",
"submitter": "Hemanth kumar <hemanth.bommireddy195@gmail.com>",
"authors": "Hemanth kumar <hemanth.bommireddy195@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42796"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: SOAR spectroscopy of three TROVE TNS candidates",
"version": 2,
"editedBy": "Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Hemanth kumar <hemanth.bommireddy195@gmail.com>",
"editedOn": 1763845744924,
"createdOn": 1763796492677,
"submitter": "Hemanth kumar <hemanth.bommireddy195@gmail.com>",
"circularId": 42796,
"submittedHow": "web"
},
"message_text": "Hemanth Bommireddy (U de Chile), Regis Cartier (UA), Felipe Olivares (U Hawaii), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) spectroscopy team:\n\nWe report spectroscopic observations of the transients AT2025adgp, AT2025adhf, and AT2025adhs obtained with the SOAR telescope on 2025-11-14 at 04:10:05 UTC (PI: Bommireddy). For each source, we obtained an exposure of approximately 900s. The spectra were preliminarily reduced and classified using the NGSF spectral classification software (Goldwasser et al. 2022). Based on the reported redshifts (GCN 42675), the top 3 template fits for each event are listed below.\n\n| event | SN type/event/instrument (χ²/dof) |\n| -----------| --------------------------------------------------------------------------- |\n| AT2025adgp | II/2013fs/KAST (~0.83), Ic-BL/1998bw/DFOSC (~0.82), IIn/2010jl/KAST (~0.88)\n| AT2025adhf | Ic-BL/1998bw/DFOSC (~1.96), Ic-BL/1998bw/EFOSC2-3.6 (~1.99), Ic-BL/1998bw/DFOSC (~2.06)|\n| AT2025adhs | SLSN-I/PTF10aagc/LRIS (~1.57), Ia-pec/2000cx/KAST (~1.61), SLSN-I/PTF12dam/DBSP (~1.62)|\n\nWe thank the SOAR staff for their support during these observations.\n",
"published": "2025-11-22T21:09:05.565059Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-22T21:09:05.565083Z",
"modified": "2025-11-22T21:09:05.585215Z",
"targets": []
},
{
"id": 5801162,
"topic": "gcn.circulars",
"uuid": "95dc3725-6455-465a-a865-b5cf34537560",
"title": "LIGO/Virgo/KAGRA S251112cm: SOAR spectroscopy of three TROVE TNS candidates",
"submitter": "Hemanth kumar <hemanth.bommireddy195@gmail.com>",
"authors": "Hemanth kumar <hemanth.bommireddy195@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42796"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: SOAR spectroscopy of three TROVE TNS candidates",
"createdOn": 1763796492677,
"submitter": "Hemanth kumar <hemanth.bommireddy195@gmail.com>",
"circularId": 42796,
"submittedHow": "web"
},
"message_text": "Hemanth Bommireddy (U de Chile), Regis Cartier (UA), Felipe Olivares (U Hawaii), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) spectroscopy team:\n\nWe report spectroscopic observations of the transients AT2025adgp, AT2025adhf, and AT2025adhs obtained with the SOAR telescope on 2025-11-14 at 04:10:05 UTC (PI: Bommireddy). For each source, we obtained an exposure of approximately 900s. The spectra were preliminarily reduced and classified using the NGSF spectral classification software (Goldwasser et al. 2022). Based on the reported redshifts (GCN 42675), the top 3 template fits for each event are listed below.\n\n| event | SN type/event/instrument (χ²/dof) |\n| -----------| --------------------------------------------------------------------------- |\n| AT2025adgp | II/2013fs/KAST (~0.83), Ic-BL/1998bw/DFOSC (~0.82), IIn/2010jl/KAST (~0.82)\n| AT2025adhf | Ic-BL/1998bw/DFOSC (~1.96), Ic-BL/1998bw/EFOSC2-3.6 (~1.99), Ic-BL/1998bw/DFOSC (~2.06)|\n| AT2025adhs | SLSN-I/PTF10aagc/LRIS (~1.57), Ia-pec/2000cx/KAST (~1.61), SLSN-I/PTF12dam/DBSP (~1.62)|\n\nWe thank the SOAR staff for their support during these observations.\n",
"published": "2025-11-22T07:28:20.510482Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-22T07:28:20.510507Z",
"modified": "2025-11-22T07:28:20.517080Z",
"targets": []
},
{
"id": 5800641,
"topic": "gcn.circulars",
"uuid": "64860ce5-368c-4d67-9727-b704ac954cbb",
"title": "LIGO/Virgo/KAGRA S251112cm: SVOM/VT optical observations and preliminary results",
"submitter": "Yinuo Ma <mayn@bao.ac.cn>",
"authors": "Yinuo Ma <mayn@bao.ac.cn>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42777"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: SVOM/VT optical observations and preliminary results",
"createdOn": 1763623294170,
"submitter": "Yinuo Ma <mayn@bao.ac.cn>",
"circularId": 42777,
"submittedHow": "web"
},
"message_text": "Y. N. Ma, L. P. Xin, Z. H. Yao, 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/VT performed the Target of Opportunity observations of 3 candidates of S251112cm reported by LIGO/Virgo/KAGRA (GCN 42650, GCN 42690). SVOM/VT began observing the field at 2025-11-17, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. \n\nWe observed AT2025adhf (GCN 42675, GCN 42724), AT2025adkl (GCN 42691), and AT2025addc (GCN 42658), which were reported by the Vera C. Rubin Observatory (GCN 42707). We found that AT2025adhf is located within a galaxy, while AT2025adkl is situated at a galaxy's edge. Here we provide the total magnitudes of the supernovae and the galaxies (using the galactic nuclei as the photometric center), since we do not have the templates for this sources. AT2025addc is an isolated source, and we also provide its magnitude. The magnitudes are:\n\nName |Observation Date(UTC) |VT_B(AB_mag) |VT_R(AB_mag) \n----------------------|----------------------|-------------|------------- \nAT2025adhf(+galaxy) |2025-11-17 |17.19+-0.01 |16.41+-0.01\nAT2025adkl(+galaxy) |2025-11-18 |20.14+-0.05 |19.50+-0.04\nAT2025addc |2025-11-17 |20.45+-0.04 |20.75+-0.07 \n\nOur photometry was not corrected for Galactic extinction.\n\nFurther analysis of these candidates is ongoing.\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.",
"published": "2025-11-20T07:21:39.903829Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-20T07:21:39.903842Z",
"modified": "2025-11-20T07:21:39.909925Z",
"targets": []
},
{
"id": 5800246,
"topic": "gcn.circulars",
"uuid": "d2918c8d-06c7-43ae-8e8e-efc870fb458f",
"title": "LIGO/Virgo/KAGRA S251112cm: EP-FXT follow-up 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/42714"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: EP-FXT follow-up observations",
"createdOn": 1763373505124,
"submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
"circularId": 42714,
"submittedHow": "web"
},
"message_text": "Q. Y. Wu, J. W. Hu, Y. Liu (NAO, CAS), B. Zhang (HKU) on behalf of the Einstein Probe (EP) team:\n\nEP-FXT performed a series of follow-up observations of the LIGO/Virgo/KAGRA gravitational-wave event S251112cm (GCN 42650, GCN 42690), with 100 galaxy-targeted observations have been completed. These observations were conducted from 2025-11-12T15:38:36 to 2025-11-14T10:28:28 (UTC), with each pointing having an exposure of approximately 300 s. EP-FXT covered 88 deg2 (8.9% in probability) of the updated sky localization area (GCN 42690)\n\nWe cross-matched all FXT detections from these pointings against the updated list of NED galaxies provided in GCN 42693, using a 100″ matching radius (for a galaxy at 100 Mpc this corresponds to an offset of ~50 kpc). Most matched sources have prior X-ray detections with FXT fluxes comparable to historical values. There are two weak sources without prior X-ray counterparts within the FXT error region. Their information is summarized below (RA/Dec in degrees with 10\" error radius (90% C.L.); fluxes are the observed ones in 0.5–10 keV):\nName | RA | Dec | Matched NED Galaxy | Sep. (arcsec) | Flux (erg/s/cm^2) | SNR\n----------------------------------------------------------------------------------------------------------------------------\nEPF_J234847.8-282639 | 357.1990 | -28.4442 | WISEA J234841.30-282641.1 | 85.2 | 7.4e-13| 6.6\nEPF_J010845.7-463304 | 17.1904 | -46.5512 | SMDG J0108452-463428 | 83.8 | 1.4e-13| 4.2\n\nIn addition, FXT detected 8 sources with no prior X-ray detections, no matches to the NED galaxies and no obvious AGN or stellar counterparts within the FXT error regions. Their information is summarized below (RA/Dec in degrees with 10\" error radius (90% C.L.); fluxes are the observed ones in 0.5–10 keV):\nName | RA | Dec | Flux (erg/s/cm^2) | SNR\n-------------------------------------------------------------------------\nEPF_J000245.6-341925 | 0.6899 | -34.3235 | 2.0e-13| 4.0\nEPF_J020544.2-520424 | 31.4343 | -52.0734 | 1.7e-13| 4.1\nEPF_J092041.9-081815 | 140.1746 | -8.3041 | 2.1e-13| 4.9\nEPF_J093255.2-020027 | 143.2301 | -2.0076 | 4.3e-13| 3.5\nEPF_J111043.0+362227 | 167.6792 | 36.3742 | 1.6e-13| 4.6\nEPF_J113825.2+432218 | 174.6051 | 43.3716 | 7.3e-14| 5.4\nEPF_J232328.1-114600 | 350.8670 | -11.7667 | 1.5e-13| 3.9\nEPF_J234628.3-290057 | 356.6177 | -29.0158 | 7.9e-13| 4.5\n\nFurther FXT observations of these candidates will be conducted.\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": "2025-11-17T10:18:32.108473Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:32.108487Z",
"modified": "2025-11-17T10:18:32.113755Z",
"targets": []
},
{
"id": 5800222,
"topic": "gcn.circulars",
"uuid": "9e8bce1b-8548-4226-9f1e-d69963ca5f06",
"title": "LIGO/Virgo/KAGRA S251112cm: Candidates from the Zwicky Transient Facility",
"submitter": "Shreya Anand <shreyasahasram08@gmail.com>",
"authors": "Shreya Anand <shreyasahasram08@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42677"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42677....1A",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Candidates from the Zwicky Transient Facility",
"createdOn": 1763086819370,
"submitter": "Shreya Anand <shreyasahasram08@gmail.com>",
"circularId": 42677,
"submittedHow": "web"
},
"message_text": "S. Anand (Stanford), R. Stein (UMD), X. J. Hall (CMU), V. Swain (IIT-B), A. Saikia (IIT-B), T. Mohan (IIT-B), V. Bhalerao (IIT-B), D. Cook (Caltech/IPAC), A. Singh (SU), M. M. Kasliwal (Caltech), E. C. Bellm (UW), M. Coughlin (UMN), T. du Laz (Caltech), V. Karambelkar (Columbia), G. Waratkar (Caltech), I. Andreoni (UNC), A. Palmese (CMU) report,\n\non behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: \n\nWe observed the localization region of the LVK sub-solar mass candidate S251112cm (GCN 42650) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2025-11-12 09:21 UTC, approximately 18 hours after merger, covering 38.3% of the probability within the 90% credible region of the LVK skymap in g- and r-bands. This estimate accounts for chip gaps. Each exposure was 300s with a median r-band depth of 21.14 mag. \n \nThe images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019), removing candidates with history of variability prior to the merger time. \n\nBecause of the nature of the GW trigger as a sub-solar mass merger candidate, we do not exclude any candidates that may be consistent with being young stripped envelope supernovae (SESNe). Disk fragmentation or core fissioning in SESNe may lead to the formation of subsolar mass neutron stars (Metzger et al. 2024, Kasliwal et al. 2025).\n\nAfter filtering, 8 transient candidates remain, all within the 95.0% localization of the skymap. Candidates marked as FAR have redshifts from Legacy Survey or from SDSS (shown below). Redshift lower limits come from Legacy Survey (l95; a conservative lower limit on the photometric redshift). We list the 8 candidates found in the table below: \n\n| ZTF Name | RA (deg) | DEC (deg) | MJD | Filt | Mag | MagErr | Redshift | Note |\n| ------------- | ---------- | --------- | -------- | ---- | ----- | ------ | --------------------------------------- | ---------------------------------------- |\n| ZTF25aceekrn* | 180.101460 | 49.047764 | 60992.43 | g | 21.04 | 0.22 | photo-z=0.14 (LS); photo-z=0.189 (SDSS) | FAR |\n| ZTF25aceekwp | 181.804049 | 55.653636 | 60992.44 | g | 21.23 | 0.20 | photo-z>0.24 (LS) | FAR |\n| ZTF25aceelgz | 190.811137 | 57.328886 | 60992.47 | g | 21.15 | 0.13 | spec-z=0.476 (SDSS) | AGN-like; w1-w2=0.97 |\n| ZTF25aceelbm | 169.544486 | 41.094776 | 60992.41 | g | 21.20 | 0.23 | photo-z=0.21 (LS); photo-z=0.24 (SDSS) | FAR |\n| ZTF25aceemla | 185.395941 | 56.586289 | 60992.46 | r | 21.25 | 0.23 | photo-z>0.28 (LS) | FAR |\n| ZTF25aceekzz | 169.076786 | 39.863435 | 60992.41 | g | 21.32 | 0.26 | photo-z=0.528 (LS) | AGN-like; ZTF pre-detections; w1-w2=1.13 |\n| ZTF25aceelmh | 184.916369 | 57.167778 | 60992.47 | g | 21.61 | 0.22 | photo-z>0.41 (LS); photo-z=0.42 (SDSS) | FAR |\n| ZTF25aceempu | 169.569004 | 35.985827 | 60992.49 | r | 21.60 | 0.21 | photo-z>0.23 (LS) | FAR |\n\n*ZTF25aceekrn (AT 2025adht) was previously reported by the TROVE team (GCN 42675) with a photo-z=0.11 +/- 0.07 (nominally consistent with the LVK distance posterior). A spectrum can help resolve this discrepancy.\n\nNone of the other candidates reported here warrant additional follow-up.\n\nAll candidates have been reported to the Transient Name Server, and some are pending assignment of a TNS name. \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. GROWTH acknowledges the generous support of the NSF under PIRE Grant No 1545949. Alert database searches are done by AMPEL (Nordin et al. 2019) and Kowalski (Duev et al. 2019). The GROWTH India Telescope (GIT, Kumar et al., 2022) is set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. Its operations are partially supported by funding from the IIT Bombay alumni batch of 1994. The Fritz and SkyPortal projects acknowledge the generous support of The Gordon and Betty Moore Foundation.",
"published": "2025-11-17T10:18:31.776216Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:31.776230Z",
"modified": "2025-11-17T10:18:31.782275Z",
"targets": []
},
{
"id": 5800220,
"topic": "gcn.circulars",
"uuid": "a1e5bce4-1356-4a57-835e-62cd2282ebec",
"title": "LIGO/Virgo/KAGRA S251112cm: FTW observations of galaxies within localization region",
"submitter": "Julius Gassert at Ludwig-Maximilians-Universität München <julius.gassert@campus.lmu.de>",
"authors": "Julius Gassert at Ludwig-Maximilians-Universität München <julius.gassert@campus.lmu.de>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42674"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42674....1G",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: FTW observations of galaxies within localization region",
"createdOn": 1763064743669,
"submitter": "Julius Gassert at Ludwig-Maximilians-Universität München <julius.gassert@campus.lmu.de>",
"circularId": 42674,
"submittedHow": "web"
},
"message_text": "Julius Gassert (CMU/LMU), Malte Busmann (LMU), Xander J. Hall (CMU), Brendan O’Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report:\n\nWe observed a sample of 19 DESI galaxies, ranked by 3D position and brightness following the methodology laid out in Hall et al. (2025), in the sky localization region of gravitational wave event S251112cm (GCN 42650) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J bands simultaneously. Observations started at 2025-11-12T17:43 (UT). Typical three-sigma limits for point sources are r, i ~ 21, and the field of view is 7’x7’. We do not identify any candidate GW counterpart in difference imaging with respect to Legacy Survey and PS1 data. The coordinates of the observed targets are listed below.\n\n| R.A. | dec |\n|---|---|\n| 164.426910134 | 37.65453732955 |\n| 165.5240393492 | 38.78722513647 |\n| 167.4811243685 | 36.94655132258 |\n| 173.5605908567 | 49.0431665104 |\n| 182.4385674509 | 56.52359456357 |\n| 182.8894005861 | 57.73745323273 |\n| 186.0084874694 | 58.38519262405 |\n| 196.9032263873 | 60.15719529696 |\n| 197.1937364898 | 62.27166824173 |\n| 250.834423606 | 70.63254712505 |\n| 341.1015299287 | -0.162034769873 |\n| 341.5808358893 | 3.210042314846 |\n| 343.2053071078 | 1.201113639068 |\n| 344.2120066199 | -8.967554297055 |\n| 344.5092848207 | -3.76968999454 |\n| 345.0369565289 | -12.80783236183 |\n| 346.7423345683 | -9.286127524436 |\n| 347.1867614296 | -12.63952485965 |\n| 349.7190055484 | -10.25928200595 |\n\nWe thank Christoph Ries from the Wendelstein Observatory staff for obtaining these observations.",
"published": "2025-11-17T10:18:31.737176Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:31.737190Z",
"modified": "2025-11-17T10:18:31.742643Z",
"targets": []
},
{
"id": 5800218,
"topic": "gcn.circulars",
"uuid": "0e2dda74-86da-437e-bc3d-c3922a4f1b41",
"title": "LIGO/Virgo/KAGRA S251112cm: Detection of two young transients by BlackGEM/MeerLICHT: AT2025adgp and AT2025adgq",
"submitter": "Paul Groot at Radboud University Nijmegen <p.groot@astro.ru.nl>",
"authors": "Paul Groot at Radboud University Nijmegen <p.groot@astro.ru.nl>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42663"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42663....1G",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Detection of two young transients by BlackGEM/MeerLICHT: AT2025adgp and AT2025adgq",
"createdOn": 1763023570662,
"submitter": "Paul Groot at Radboud University Nijmegen <p.groot@astro.ru.nl>",
"circularId": 42663,
"submittedHow": "web"
},
"message_text": "P.J. Groot (Radboud/UCT/SAAO) , H. Tranin (Barcelona), J. van Roestel (ISTA), P.M. Vreeswijk (Radboud), D. Pieterse (Radboud), G. Leloudas (DTU Space), N. Blagorodnova (Barcelona), S. Bloemen (Radboud), G. Ramsay (Armagh), S. Scaringi (Durham) report on behalf of the BlackGEM and MeerLICHT consortia: \n\n\"The BlackGEM and MeerLICHT telescopes (Groot et al., 2024) reacted to the LVK-announced gravitational wave event S251112cm (LVK2025, GCN Circ. 42650). Both telescope systems covered about 50% of the 90% error box, primarily the part located in the Southern Hemisphere. A detailed overview of observations will be given in a subsequent report. Here we report the detection of AT2025adgp (BGEM J014746.20-514925.5), and AT2025adgq (MLT J002931.8-393051.6) as two newly detected transients in the BlackGEM/MeerLICHT footprint, which, on average, had a limiting magnitude for new transients of q~19.8. \n\nAT2025adgp is located at RA, Dec (ICRS) = 01:47:46.202 -51:49:25.52 (26.942508d, -51.823756d) with an uncertainty of 0.1\" in each coordinate. It was detected on 2025-11-13 03:09:48 and 03:25:29 UT in the BlackGEM q-band (440-720 nm) filter using the BG-2 telescope, at, respectively, q=19.31+/-0.12 and q=19.29+/-0.12. The first detection was 11h50m after the LVK Trigger time. The transient is located in the southern outskirts of a face-on spiral galaxy WISExSCOS J014746.23-514922.5, listed in the Regalade catalog (Tranin et al., 2025) at a luminosity distance of D_L =246 Mpc with a large standard deviation, and in the GLADE+ (Dalya et al., 2020) catalog at D_L = 250 +/- 45 Mpc. If the galaxy is the host of AT2025adgp this would put its distance at the upper edge of consistency with the distance to S251112cm as announced by the LVK collaboration at D_S251112cm = 96 +/- 29 Mpc. \n\nAT2025adgq is located at RA,Dec (ICRS) = 00:29:31.8, -39:30:51.6 (7.38245842d, -39.5143190d) with an uncertainty of 0.1” in each coordinate. It was detected on 2025-11-13 00:03:38 and 00:04:43 UT in the BlackGEM q-band (440-720 nm) filter using the MeerLICHT telescope at, q=19.28+/-0.10 in each exposure. The first detection was 08h44m after the LVK trigger. The BlackGEM array also detected AT2025adgq on 2025-11-13 01:05:23 UT and 01:22:00 UT using the BG-2 telescope at q=19.28 +/- 0.10 and q=19.41 +/- 0.1, respectively. The transient is located in the north-eastern elongation of an oblated galaxy, WISExSCOS J002932.49-393059.7, listed in the Regalade catalog at a luminosity distance of D_L = 279 +/- 130 Mpc, and in the GLADE+ catalog at D_L = 300 +/- 68 Mpc. If the galaxy is the host of AT2025adqp this would put its distance at the upper edge of consistency with the distance to S251112cm as announced by the LVK collaboration. \n\nWe encourage spectroscopic classification of AT2025adgp and AT2025adgq to confirm their nature and distance, and therefore the possibility of them being a counterpart to S251112cm.\"\n\nReferences: \nGroot et al., 2024, PASP 136, 5003, Tranin et al., 2025, arXiv250813267T, Dalya et al., 2020, VizieR On-line Data Catalog: VII/275; LVK2025, 2025, GCN 42650\n\n",
"published": "2025-11-17T10:18:31.700467Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:31.700481Z",
"modified": "2025-11-17T10:18:31.706172Z",
"targets": []
},
{
"id": 5800212,
"topic": "gcn.circulars",
"uuid": "cad41e04-6be7-4ad2-9cd5-0918c12270a8",
"title": "LIGO/Virgo/KAGRA S251112cm: Initial GOTO-South observations",
"submitter": "kendall.ackley@warwick.ac.uk",
"authors": "kendall.ackley@warwick.ac.uk",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42658"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42658....1A",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Initial GOTO-South observations",
"version": 2,
"editedBy": "Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of kendall.ackley@warwick.ac.uk",
"editedOn": 1763001737175,
"createdOn": 1762987643407,
"submitter": "kendall.ackley@warwick.ac.uk",
"circularId": 42658,
"submittedHow": "web"
},
"message_text": "K. Ackley, B. Godson, D. O'Neill, B. P. Gompertz, M. Dyer, J. Lyman, K. Ulaczyk, S. Belkin, T. Killestein, A. Kumar, M. Pursiainen, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, J. Casares Velásquez, L. K. Nuttall, report on behalf of the GOTO collaboration:\n\nWe carried out optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al 2024) in response to the LIGO/Virgo/KAGRA gravitational wave candidate event S251112cm (GCN 42650).\n\nTargeted observations were performed by GOTO-South (Siding Spring, Australia) starting at 2025-11-12 16:09:51 UT, (+0.85h post trigger) and continued through to 2025-11-12 17:51:21 UT (+2.54h post trigger). A total of 39 image sets with exposures of 4x60s and 4x90s were taken across 6 unique pointings, covering 250.5 sq. degrees within the 90% localisation contour of the initial skymap. We covered approximately 14.6% of the total 2D localisation probability with an average 5-sigma depth of L~19.9 mag (AB). \n\nImages were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks.\n\nWithin the initial skymap, we identify 2 optical sources within the 90% contour and 1 optical source within the 99% probability contour. We find no convincing evidence of excess flux in either GOTO25jyg/AT2025addc or GOTO25jya/AT2025adcv prior to the GW trigger time in previous GOTO observations or the ZTF observations provided by the Lasair broker (Smith et al. 2019). The ATLAS forced photometry server (Shingles et al. 2021) returns recent detections for GOTO25jyg and GOTO25jya, albeit at low significance. We encourage further analysis to confirm these pre-detections.\n\nWe note that GOTO25jya appears to be associated with a GLADE+ galaxy HyperLEDA 422311 with zphot ~ 0.01 (D_L~474 Mpc) which, if correct, would put it outside the nominal luminosity distance estimates of S251112cm. \n\nWe do not find a host galaxy underlying GOTO25jyg. There is a galaxy located 9.27 arcsec from the candidate’s position within the Legacy DR10 photometric redshift catalog with zphot ~ 0.3 (Dey et al. 2019). \n\nGOTO25jye/AT2025adcy is located outside of the 90% probability contour of the initial skymap and is potentially associated with a GLADE+ galaxy HyperLEDA 389528 at zphot ~ 0.13 (D_L~664 Mpc). This association would make this candidate unlikely to be related to S251112cm.\n\n\n| Internal name | IAU name | RA(J2000) | Dec(J2000) | Mag(AB) |\n| ------------- | ---------- | ----------- | ------------ |--------------- |\n| GOTO25jyg | AT2025addc | 04:55:26.13 | -53:09:43.61 | 19.93 +/- 0.20 |\n| GOTO25jya | AT2025adcv | 03:05:58.60 | -54:09:06.60 | 19.30 +/- 0.10 |\n| GOTO25jye | AT2025adcy | 04:35:28.56 | -57:28:31.64 | 19.71 +/- 0.12 |\n\t\n\nMagnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and not corrected for Galactic extinction. Continued observations are planned from both GOTO sites, weather permitting.\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, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC).\n",
"published": "2025-11-17T10:18:31.601875Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:31.601891Z",
"modified": "2025-11-17T10:18:31.607361Z",
"targets": []
},
{
"id": 5800189,
"topic": "gcn.circulars",
"uuid": "46205fe6-09b6-48ec-9ab9-e05fbb63cbcd",
"title": "LIGO/Virgo/KAGRA S251112cm: TROVE Vetting of TNS Candidates",
"submitter": "Noah Franz at University of Arizona/Steward Observatory <noahfranz13@gmail.com>",
"authors": "Noah Franz at University of Arizona/Steward Observatory <noahfranz13@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42675"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42675....1F",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: TROVE Vetting of TNS Candidates",
"createdOn": 1763073011684,
"submitter": "Noah Franz at University of Arizona/Steward Observatory <noahfranz13@gmail.com>",
"circularId": 42675,
"submittedHow": "web"
},
"message_text": "N. Franz (U. Arizona), N. Vieira (Northwestern), C. D. Kilpatrick (Northwestern), D. J. Sand (U. Arizona), B. Subrayan (U. Arizona), G. Hosseinzadeh (UC San Diego), M. Shrestha (Monash U), K. D. Alexander (U. Arizona), W. Fong (Northwestern), report on behalf of the TROVE collaboration:\n\nWe analyzed candidate counterparts to the LIGO/Virgo/KAGRA (LVK) gravitational wave event S251112cm (GCN 42650) using the Multi-messenger Tool for Rapid Object Vetting and Examination (TROVE). We searched within the 95th percentile localization region for candidate optical counterparts in host galaxies at the approximate luminosity distance of S251112cm. We further crossmatch to minor planet and point source catalogs and rule out sources that do not appear photometrically similar to kilonova light curves. For additional details, see the vetting procedures described in N. Franz, et al., 2025, arXiv:2510.17104.\n\nBelow, we report all candidates that remain viable after running our vetting procedure using publicly available information on all publicly reported sources, to date, on the Transient Name Server (TNS). We include their TNS identifier, coordinates, cumulative probability at the coordinate location in the latest LVK map, most likely host redshift, most recent magnitude, and the initial reporting group. Candidates are ranked using a scoring procedure designed to identify kilonova counterparts to GW events (N. Franz, et al., 2025, arXiv:2510.17104). The reported candidates are not clearly identified as kilonovae, but we note that the progenitor system of S251112cm is poorly constrained given the exceptional attributes of the event as reported by LIGO: a probability of the system containing a neutron star < 8%, probability of containing a sub-solar mass object >99%, and a chirp mass in the range 0.1 to 0.87 solar masses.\n\n\n| TNS Name | RA [HMS] | Dec [DMS] | Localization Probability Contour | Most likely Host-z | Most recent public magnitude | Discovery Survey | Comments |\n| ------- | ------ | ------- | ------- | ------- | ------- | ------- | ------- |\n| AT2025adht | 12:00:24.350 |+49:02:51.95 | 0.83 | 0.11 +/- 0.07 (photo-z) | g=21.4 +/- 0.2 | ZTF | |\n| AT2025adgp | 01:47:46.202 | -51:49:25.52 | 0.20 | 0.06 +/- 0.02 (photo-z) | o=19.1 +/- 0.05 | BlackGEM | ATLAS pre-detection ~6 hours before S251112cm. This candidate was initially presented in GCN42663 and the ATLAS pre-detections were noted in GCN 42666. |\n| AT2025adhf | 02:43:44.411 | -55:19:06.44 | 0.15 | 0.11 +/- 0.02 (photo-z) | o=19.22 +/- 0.05 | ATLAS | ATLAS pre-detections in the ~week leading up to S251112cm. |\n| AT2025adhs | 04:12:56.396 | -54:11:46.41 | 0.09 | 0.04 (spec-z) | o=20.71 +/- 0.22 | BlackGEM | |\n\nWe encourage additional follow up of these candidates to determine whether they remain viable counterparts to S251112cm. We note that there are 10 other transients reported to the TNS in the 95% localization region that we rule out for other reasons (e.g., excessive pre-detections, incorrect host distance as compared to S251112cm, etc.): AT2025adhj, AT2025addc, AT2025adhr, AT2025adhu, AT2025adhg, AT2025addb, AT2025adhh, AT2025adda, AT2025adhe, AT2025adgq.",
"published": "2025-11-17T10:18:31.289915Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:31.289929Z",
"modified": "2025-11-17T10:18:31.295691Z",
"targets": []
},
{
"id": 5800182,
"topic": "gcn.circulars",
"uuid": "2e7e832d-ad92-4c6f-a6d2-a5dae459bf8d",
"title": "LIGO/Virgo/KAGRA S251112cm: ATLAS pre-detections of AT2025adgp and AT2025adgq",
"submitter": "James Gillanders at University of Oxford <jhgillanders.astro@gmail.com>",
"authors": "James Gillanders at University of Oxford <jhgillanders.astro@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42666"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42666....1G",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: ATLAS pre-detections of AT2025adgp and AT2025adgq",
"createdOn": 1763035943691,
"submitter": "James Gillanders at University of Oxford <jhgillanders.astro@gmail.com>",
"circularId": 42666,
"submittedHow": "web"
},
"message_text": "J. H. Gillanders (Oxford), S. J. Smartt, K. W. Smith (Oxford/QUB), S. Srivastav, H. Stevance, F. Stoppa, A. Cooper (Oxford), M. Nicholl, D. R. Young, C. R. Angus, M. D. Fulton, T. Moore, A. Aamer, M. McCollum, S. Sim, J. Weston, X. Sheng, D. Magill, P. Ramsden (QUB), L. Shingles (GSI/QUB), L. Rhodes (TSI/McGill), L. Denneau, J. Tonry, H. Weiland, R. Siverd (IfA, University of Hawaii), N. Erasmus, W. Koorts (South African Astronomical Observatory), A. Rest (STScI), T.-W. Chen (NCU), C. Stubbs (Harvard), J. Sommer (LMU/QUB), B. Schmidt (ANU):\n\nWe are currently observing the skymap of the LIGO/Virgo/KAGRA GW event S251112cm (LVK Collaboration, GCN 42650) with ATLAS (Tonry et al., 2018, PASP, 13, 164505; Licandro et al., 2023, arXiv:2302.07954). ATLAS is a quintuple 0.5-m optical telescope survey system (Hawaii x2, South Africa, Chile, Tenerife) employing three filters, cyan, orange and ‘clear’. In our primary NASA mission for Near-Earth Object discovery, we cover the entire visible night sky every 24 hours to a magnitude depth of m ~ 19.5, weather and Moon permitting. We will report our candidate discoveries in an upcoming GCN.\n\nGroot et al. (GCN 42663) report on BlackGEM/MeerLICHT observations of the GW skymap of S251112cm (GCN 42650), and they present two candidate counterparts: AT2025adgp and AT2025adgq. \n\nHere, we note that both AT2025adgp and AT2025adgq have historical detections in ATLAS, which precede the GW detection. The public ATLAS data (for these and any other transient) are accessible through the ATLAS Forced Photometry Server (Shingles et al. AstroNote #2021-7).\n\nMore specifically:\nAT2025adgp was first detected on MJD 60991.136 (~0.5 days pre-GW) in the c-band with magnitude, m_c = 19.22 +/- 0.25 (AB) mag.\nAT2025adgq was first detected on MJD 60988.111 (~3.5 days pre-GW) in the o-band with magnitude, m_o = 19.03 +/- 0.18 (AB) mag.\n\nGiven these pre-detections, we expect that both AT2025adgp and AT2025adgq are young, rising supernovae, unrelated to the GW signal, S251112cm. However, the exact nature of the optical counterpart to a sub-solar-mass compact object merger event is uncertain, and so we cannot rule out that these transient phenomena are related in some way. Further monitoring of these candidate events will occur with ATLAS.\n\nThe Asteroid Terrestrial-impact Last Alert System (ATLAS) project is primarily funded to search for Near-Earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, University of Oxford, the Queen's University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile.",
"published": "2025-11-17T10:18:31.184818Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:31.184834Z",
"modified": "2025-11-17T10:18:31.190487Z",
"targets": []
},
{
"id": 5800181,
"topic": "gcn.circulars",
"uuid": "d508970f-d36f-46cb-9c89-e284da47e78c",
"title": "LIGO/Virgo/KAGRA S251112cm: NED Galaxies in the 3-Initial Localization Volume",
"submitter": "David Cook at Caltech/IPAC-NED <dcook@ipac.caltech.edu>",
"authors": "David Cook at Caltech/IPAC-NED <dcook@ipac.caltech.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42653"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42653....1C",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: NED Galaxies in the 3-Initial Localization Volume",
"createdOn": 1762966807827,
"submitter": "David Cook at Caltech/IPAC-NED <dcook@ipac.caltech.edu>",
"circularId": 42653,
"submittedHow": "web"
},
"message_text": "David O. Cook (Caltech/IPAC), Rick Ebert (Caltech/IPAC), George Helou (Caltech/IPAC), Joseph M. Mazzarella (Caltech/IPAC), Marion Schmitz (Caltech/IPAC), and Leo Singer (NASA/GSFC)\n\nOn behalf of the NASA/IPAC Extragalactic Database (NED) Team.\n\nWe spatially cross-matched the LVK S251112cm-3-Initial sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023; https://ned.ipac.caltech.edu/NED::LVS/) which is a subset of NED with a redshift or redshift-independent distance less than 1000 Mpc. We find 7731 galaxies within the 90% containment volume, and we list here the top 20 galaxies sorted by the joint probability of the 3D localization and the WISE W1 luminosity (an observable proxy for stellar mass). For the full or top 20 list of galaxies in the 90% volume go either to the NED Gravitational Wave Followup service at https://ned.ipac.caltech.edu/uri/NED::GWF/ or click on the following links:\n\nFull List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S251112cm/3 \nTop 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S251112cm/3/20\n\nThe NED-GWF service provides downloadable galaxy lists and visualizations for candidate host galaxies. For each GW alert, these products are automatically generated and made available within minutes to expedite efficient electromagnetic follow-up observations. The NED top 20 list is sorted by the joint probability of the 3D localization and the WISE W1 luminosity, but users can sort on additional pre-computed prioritization metrics (star formation rate, P_3D * P_SFR; and specific star formation rate, P_3D * P_sSFR; etc.) which are available via downloading the entire galaxy list inside the event's probability volume.\n\n| objname| ra| dec|objtype| DistMpc|DistMpc_unc| m_NUV| m_NUV_unc| m_Ks| m_Ks_unc| m_W1| m_W1_unc| P_3D|P_3D_LumW1|\n|-------------------------|--------------|--------------|-------|-----------|-----------|------------|------------|------------|------------|------------|------------|--------|----------|\n| NGC 2960| 145.15161| 3.57703| G| 76.97| 7.94| 17.522| 0.003| 9.783| 0.038| 9.672| 0.002|1.71e-05| 1.08e-08|\n| IC 1471| 347.18676| -12.63948| G| 83.00| 17.58| 17.246| 0.027| 10.334| 0.035| 10.290| 0.006|1.79e-05| 7.44e-09|\n| NGC 7396| 343.09426| 1.09241| G| 81.16| 8.50| 17.854| 0.004| 8.699| 0.022| 8.557| 0.012|3.66e-06| 7.25e-09|\n| UGC 05226| 146.51479| 4.40348| G| 66.86| 15.78| 18.763| 0.092| 10.211| 0.041| 10.083| 0.089|2.17e-05| 7.08e-09|\n| IC 0564| 146.58792| 3.07130| G| 75.75| 2.62| null| null| 10.033| 0.035| 10.010| 0.006|1.51e-05| 6.79e-09|\n| NGC 3070| 149.52893| 10.35980| G| 60.25| 5.89| 18.225| 0.068| 9.260| 0.030| 9.503| 0.006|1.45e-05| 6.56e-09|\n| IC 1464B| 345.79587| -8.98909| G| 105.88| 0.59| null| null| 10.015| 0.036| 9.741| 0.006|5.69e-06| 6.38e-09|\n|WISEA J100012.04+093856.0| 150.05020| 9.64890| G| 78.82| 0.30| null| null| 11.073| 0.096| 10.233| 0.006|1.53e-05| 6.05e-09|\n| UGCA 150| 137.70611| -8.89069| G| 28.38| 0.82| null| null| 7.704| 0.006| 7.044| 0.041|5.28e-06| 5.11e-09|\n| IC 1633| 17.48145| -45.93116| G| 96.06| 3.43| null| null| 8.396| 0.025| 8.999| 0.006|2.80e-06| 5.10e-09|\n| NGC 3540| 167.31704| 36.02108| G| 93.24| 0.04| 19.626| 0.150| 10.168| 0.041| 10.319| 0.006|9.87e-06| 5.03e-09|\n| NGC 2987| 146.42281| 4.94189| G| 54.46| 0.58| 17.338| 0.002| 10.146| 0.048| 9.912| 0.006|1.97e-05| 4.99e-09|\n| NGC 7646| 351.02906| -11.86050| G| 79.59| 2.73| 16.328| 0.004| 10.358| 0.037| 8.371| 0.005|2.21e-06| 4.94e-09|\n| MCG -01-24-010| 140.09147| -7.88074| G| 53.94| 2.54| 15.885| 0.007| 10.054| 0.032| 9.821| 0.030|1.78e-05| 4.81e-09|\n| ESO 197- G 021| 31.13585| -52.17213| G| 87.54| 0.39| null| null| 9.099| 0.026| 9.375| 0.006|4.26e-06| 4.56e-09|\n| NGC 4187| 183.37201| 50.74150| G| 120.62| 5.52| 18.691| 0.027| 9.772| 0.027| 9.930| 0.006|3.73e-06| 4.56e-09|\n| UGC 05267| 147.47044| 9.09562| G| 80.08| 3.03| null| null| 10.147| 0.042| 10.208| 0.006|1.08e-05| 4.52e-09|\n| NGC 7364| 341.10153| -0.16213| G| 76.48| 8.25| 16.366| 0.001| 9.478| 0.028| 9.218| 0.003|4.69e-06| 4.46e-09|\n| NGC 0010| 2.14394| -33.85835| G| 87.84| 3.70| null| null| 9.205| 0.042| 9.975| 0.006|7.18e-06| 4.45e-09|\n| UGC 05855| 161.15400| 26.18153| G| 91.46| 2.06| 17.681| 0.037| 10.212| 0.028| 10.184| 0.006|7.99e-06| 4.45e-09|\n\nTable 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S251112cm sorted by the joint probability of 3D position and WISE W1 luminosity (P_3D * P_LumW1). Galaxy is the NED preferred name. RA and Dec are the Equatorial coordinates in degrees (J2000). Objtype is the object type of the galaxy candidate. Distance is the distance to the galaxy in Mpc. m_NUV and mErr_NUV are the apparent magnitude and error from GALEX. m_Ks and mErr_Ks are the apparent magnitude and error from 2MASS. m_W1 and mErr_W1 are the apparent magnitude and error from AllWISE. P_3D is the probability that the galaxy is in the volume given the distance of GW event. P_3D_LumW1 is the joint probability within the volume weighted by the WISE1 luminosity of the galaxy (P_3D * P_LumW1). \n",
"published": "2025-11-17T10:18:31.160680Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:31.160695Z",
"modified": "2025-11-17T10:18:31.166213Z",
"targets": []
},
{
"id": 5800113,
"topic": "gcn.circulars",
"uuid": "d12501a3-af6c-4be5-b4d2-be2787ef08e5",
"title": "LIGO/Virgo/KAGRA S251112cm: Identification of a GW compact binary merger candidate",
"submitter": "Alicia Calafat <alicia.calafat@ligo.org>",
"authors": "Alicia Calafat <alicia.calafat@ligo.org>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42650"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42650....1L",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Identification of a GW compact binary merger candidate",
"createdOn": 1762962925787,
"submitter": "Alicia Calafat <alicia.calafat@ligo.org>",
"circularId": 42650,
"submittedHow": "web"
},
"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe identified the compact binary merger candidate S251112cm during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-11-12 15:18:45.362 UTC (GPS time: 1446995943.362). The candidate was found by the MBTA SSM [1] analysis pipeline.\n\nS251112cm is an event of interest because its false alarm rate, as estimated by the online analysis, is 5.1e-09 Hz, or about one in 6 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S251112cm\n\nThe analysis which found this candidate used a template bank including sub-solar-mass components. The usual classification probabilities for BNS, NSBH, or BBH binaries versus Terrestrial noise are not calculated for this candidate. The probability of matter remaining outside the final compact object (HasRemnant) [2] is not estimated either.\n\nAssuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass between 1 and 3 solar masses (HasNS) is 8%. [2] The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. The probability that the lighter compact object is below 1 solar mass (HasSSM) is >99%.\n\nThe source chirp mass falls with highest probability in the bin (0.1, 0.87) solar masses, assuming the candidate is astrophysical in origin.\n\nTwo sky maps are available at this time and can be retrieved from the GraceDB event page:\n * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices about 57 seconds after the candidate event time.\n * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time.\n\nThe preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 1220 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 96 +/- 29 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234\n [2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [3] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013",
"published": "2025-11-17T10:18:30.181492Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:30.181508Z",
"modified": "2025-11-17T10:18:30.187370Z",
"targets": []
},
{
"id": 5800112,
"topic": "gcn.circulars",
"uuid": "5ec62796-31eb-48ce-9b97-0bc044b6f493",
"title": "LIGO/Virgo/KAGRA S251112cm: Coverage and upper limits from MAXI/GSC observations",
"submitter": "Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>",
"authors": "Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42659"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42659....1H",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Coverage and upper limits from MAXI/GSC observations",
"createdOn": 1763000967453,
"submitter": "Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>",
"circularId": 42659,
"submittedHow": "web"
},
"message_text": "H. Hiramatsu, S. Sugita, M. Serino, Y. Kawakubo, Y. Kondo (AGU)\nH. Negoro, M. Nakajima, K. Takagi (Nihon U.),\nN. Kawai, T. Mihara, (RIKEN),\n\nreport on behalf of the MAXI team:\n\nWe examined MAXI/GSC all-sky X-ray images (2-20 keV)\nafter compact binary merger candidate S251112cm at 2025-11-12 15:18:45.362 UTC (GCN #42650).\n\nAt the trigger time of S251112cm, the high-voltage of MAXI/GSC was on.\nThe instantaneous field of view of GSC at the GW trigger time covered 1% of the 90% credible region\nof the bayestar sky map, in which we found no significant new X-ray source.\nThe first one-orbit (92 min) scan observation with GSC after the event covered 72%\nof the 90% credible region of the bayestar skymap from 15:18:45 to 16:50:09 UTC (T0+0 to T0+5484 sec).\n\nNo significant new source was found in the region in the one-orbit scan observation.\nA typical 1-sigma averaged upper limit obtained in one scan observation\nis 20 mCrab at 2-20 keV.\n\nIf you require information about X-ray flux by MAXI/GSC at specific coordinates,\nplease contact the submitter of this circular by email.",
"published": "2025-11-17T10:18:30.154251Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:30.154266Z",
"modified": "2025-11-17T10:18:30.159982Z",
"targets": []
},
{
"id": 5800082,
"topic": "gcn.circulars",
"uuid": "2e7feb2b-8ae4-4e86-a460-0a51cca88890",
"title": "LIGO/Virgo/KAGRA S251112cm: Upper limits from Fermi-GBM Observations",
"submitter": "Angus Jameson <abj0023@uah.edu>",
"authors": "Angus Jameson <abj0023@uah.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42655"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.42655....1B",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Upper limits from Fermi-GBM Observations",
"createdOn": 1762983477642,
"submitter": "Angus Jameson <abj0023@uah.edu>",
"circularId": 42655,
"submittedHow": "web"
},
"message_text": "S. Bala (USRA) & A. Jameson (UAH) reports on behalf of the Fermi-GBM Team:\n\nFor S251112cm (GCN 42650) and using the initial/updated bayestar/Bilby skymap, Fermi-GBM was observing 68.6% of the localization probability at event time.\n\nThere was a Fermi-GBM onboard trigger 784653403/251112637, around two mins before the event time of the LIGO/Virgo/KAGRA (LVK) detection of GW S251112cm, due to local particles (GCN 42652). An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM also identified no counterpart candidates. The GBM targeted search, the most sensitive, coherent search for GRB-like signals, was run from +/-30 s around merger time, and also identified no counterpart candidates.\n\nPart of the LVK localization region is behind the Earth for Fermi, located at an RA=4.4, Dec=25.2 with a radius of 68 degrees. We therefore set upper limits on impulsive gamma-ray emission for the GW localization region visible to Fermi at merger time. Using the representative soft, normal, and hard GRB-like templates described in arXiv:1612.02395, we set the following 3 sigma flux upper limits over 10-1000 keV, weighted by GW localization probability (in units of 10^-7 erg/s/cm^2):\n\nTimescale Soft Normal Hard (Please put these in the appropriate units for 10^-7 erg/s/cm^2)\n------------------------------------\n0.128 s: 4.1 6.1 7.7\n1.024 s: 2.0 2.7 3.4\n8.192 s: 1.0 1.4 1.3\n\nAssuming the median luminosity distance of 96 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^47 erg/s):\n\nTimescale Soft Normal Hard\n------------------------------------\n0.128s: 6.9 9.6 19.8\n1.024s: 3.3 4.2 8.7\n8.192s: 1.7 2.2 3.3",
"published": "2025-11-17T10:18:29.690200Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-17T10:18:29.690214Z",
"modified": "2025-11-17T10:18:29.695505Z",
"targets": []
},
{
"id": 5799940,
"topic": "gcn.circulars",
"uuid": "481839b5-7db6-467c-9ebd-1122cbbd466d",
"title": "LIGO/Virgo/KAGRA S251112cm: Observations with the NSF-DOE Vera C. Rubin Observatory",
"submitter": "Sean MacBride at University of Zurich <sean.p.macbride@gmail.com>",
"authors": "Sean MacBride at University of Zurich <sean.p.macbride@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42707"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Observations with the NSF-DOE Vera C. Rubin Observatory",
"createdOn": 1763335353838,
"submitter": "Sean MacBride at University of Zurich <sean.p.macbride@gmail.com>",
"circularId": 42707,
"submittedHow": "web"
},
"message_text": "Sean MacBride (University of Zurich), Erin Howard, Ian Sullivan, Peter Yoachim, Eric Bellm (University of Washington), Shreya Anand (Stanford University), Federica Bianco (University of Delaware), Tiago Ribeiro, Lynne Jones, Alysha Shugart, Narayan Khadka, Kshitija Kelkar, Danica Zilkova, Kevin Fanning, Paulina Venegas, Kate Napier, Erik Dennihy, Anastasia Alexov, Bob Blum (NSF-DOE Vera C Rubin Observatory), Yousuke Utsumi (National Astronomical Observatory of Japan), Robert Lupton (Princeton University), Keith Bechtol (University of Wisconsin-Madison), reporting on behalf of NSF-DOE Vera C Rubin Observatory:\n\nWe observed the localization region of the sub-solar mass merger S251112cm, reported by LIGO/Virgo/KAGRA (GCN 42650, GCN 42690) with the 9.6 square degree field of view LSST Camera mounted on the 8.4-m Simonyi Survey Telescope at the Vera C. Rubin Observatory. As reported in GCN 42690, S251112cm has a reported 90% localization area of 1681 square degrees and an expected false alarm rate of approximately one in four years. This is the first Target-of-Opportunity observation with Rubin Observatory since the transition to operations in late October 2025.\n\nRubin Observatory is in an early operations period of continued system optimization, prior to beginning sustained LSST observations [1]. During this period, data quality and acquisition rate are variable. Not all data products that will be available during the Legacy Survey of Space and Time (LSST) operations are currently available [2]. \n\nObservations were conducted through engagement of the new Rubin Target-of-Opportunity advisory board, as a sub-solar mass merger does not meet the typical alert quality criteria for Rubin Target-of-Opportunity (ToO) observation [3]. The observing strategy for this event is to image the localization area in LSST g and i bands, with one 30 second visit for each band, on nights 0, 2, 4, and 6 of the observing campaign.\n\nOn November 15 2025, at 01:49:27 UTC, we began observing the localization region of S251112cm, using the initial localization information provided in GCN 42650. We observed 39.2% (849.1 deg^2) of the localization area in the g-band, and 33.5% (754.9 deg^2) of the localization area in the i band. The difference in coverage was due to the localization area of S251112cm setting early in the night in Chile, before the telescope could observe the region in i band. For these observations, we reached a median depth of 24.8 mag in g band, 23.7 mag in the i band.\n\n\n\nDue to the lack of prior Rubin observations in most of the imaging area, we performed image differencing against DECam templates. To support the usage of DECam templates, we devised a custom image processing task to create DECam templates from DES templates for use with LSSTCam observations. Apart from the DECam template task, we utilize the standard LSST data release production pipeline to obtain difference images and photometry on difference image sources [4]. \n\nWith only a single epoch of observations at Rubin Observatory, we are unable to characterize viable candidates from Rubin observations alone. Here, we report on candidates reported in GCN 42658, 42663, 42666, 42675, 42677, 42681, 42682, and 42691. We do not recover several candidates from these GCN’s for one of many reasons: lack of signal in the difference images, poor image subtraction near the source, or a lack of imaging in the region. Here, we report the candidates that pass these criteria, and comment on any notable nearby galaxies, given the reported luminosity distance from LVK (GCN 42650).\n\nWe perform visual inspection on difference images that are coincident with previously reported candidates. We positively detect AT2025adgq, AT2025adhf, AT2025adkl, AT2025adjp, and AT2025addc. AT2025adhf and AT2025adkl were only detected unambiguously in one band (g and i respectively). Whether they are not detected in the other band is still under investigation.. AT2025adgq is detected unambiguously in two bands, separated from a host galaxy by ~10 arcseconds. AT2025adhf is nuclear to a barred spiral galaxy (WISEA J024344.38-551906.1), but its WISE colors are not consistent with the host being an AGN. AT2025adkl is offset by 90’ from a galaxy within the NED volume (GCN 42653), slightly offset from a small distant galaxy, and detected unambiguously in one band. AT2025adjp and AT2025addc are isolated sources detected unambiguously in two bands. \n\nHere we report difference photometry for the aforementioned candidates:\n\n| AT Name | Observation Date [UTC] | RA | Dec | g | unc_g | i | unc_i |\n|------------|------------------------|---------|----------|-------|-------|-------|-------|\n| AT2025adgq | 2025-11-15 | 7.3825 | -39.5143 | 19.55 | 0.005 | 19.52 | 0.003 |\n| AT2025adhf | 2025-11-15 | 40.9351 | -55.3184 | - | - | 19.21 | 0.004 |\n| AT2025adkl | 2025-11-15 | 7.5357 | -41.0787 | 21.58 | 0.014 | - | - |\n| AT2025adjp | 2025-11-15 | 4.5396 | -33.8543 | 21.17 | 0.010 | 20.90 | 0.016 |\n| AT2025addc | 2025-11-15 | 73.8589 | -53.1621 | 20.91 | 0.009 | 21.25 | 0.022 |\n\nAnalysis of these candidates is ongoing. We will continue to observe the localization area of S251112cm in the coming days according to the observing plan.\n\nWe thank all who contributed to the design and implementation of the Vera C. Rubin Observatory Target-of-Opportunity system, including but not limited to, the LSST Transients and Variable Stars Science Collaboration Multiwavelength Characterization and Counterparts subgroup. We especially thank the Rubin Observatory observers, who are instrumental to the performance and success of the LSST.\n\nThis material is based upon work supported in part by the National Science Foundation through Cooperative Agreements AST-1258333 and AST-2241526 and Cooperative Support Agreements AST-1202910 and 2211468 managed by the Association of Universities for Research in Astronomy (AURA), and the Department of Energy under Contract No. DE-AC02-76SF00515 with the SLAC National Accelerator Laboratory managed by Stanford University. Additional Rubin Observatory funding comes from private donations, grants to universities, and in-kind support from LSST-DA Institutional Members.\n\n[1] sitcomtn-005.lsst.io, §6\n\n[2] lse-163.lsst.io\n\n[3] www.inspirehep.net/literature/2846480 \n\n[4] pstn-019.lsst.io\n",
"published": "2025-11-16T23:23:45.817985Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-16T23:23:45.818010Z",
"modified": "2025-11-16T23:25:06.995855Z",
"targets": []
},
{
"id": 5798959,
"topic": "gcn.circulars",
"uuid": "2667eec6-8f72-4863-9248-69f00fd375db",
"title": "LIGO/Virgo/KAGRA S251112cm: GRANDMA observations of the skymap",
"submitter": "antier@ijclab.in2p3.fr",
"authors": "antier@ijclab.in2p3.fr",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42699"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: GRANDMA observations of the skymap",
"createdOn": 1763241003147,
"submitter": "antier@ijclab.in2p3.fr",
"circularId": 42699,
"submittedHow": "web"
},
"message_text": "P. Hello (IJCLAB), D. Akl (NYUAD), S. Antier (IJCLAB), A. Klotz (IRAP), M. Mazek (FZU), M. Pillas (IAP), O. Pyshna (Caltech), C. Andrade (UMN), M. Coughlin (UMN), C. Douzet (IJCLAB), S. Karpov (FZU), T. duLaz (Caltech), R. LeMontagner (IJCLAB), C. Limonta (OCA), Y. Rajabov (UBAI), D. Turpin (CEA-AIM) on behalf of the GRANDMA collaboration:\n\nWe observed the S251112cm (Initial, as provided by GCN 42650, LVK collaboration) sky localization area with wide field telescopes TAROT/TRE, TAROT/TCH, TAROT/TCA, FRAM-FZU,together with the 60 cm telescope at Les Makes Observatory. Observations started at 2025-11-12 17:14 UTC, e.g 1h56 after the trigger time and during 14h. We used the SkyPortal application (skyportal.io) and associated services to monitor this observational campaign (Coughlin et al. 2018, 2023).\n\nOur sensivity map of the GW sky localization area has been computed using Pillas et al., 2025 and is accessible at https://grandma-owncloud.ijclab.in2p3.fr/index.php/s/TqGach7PpbM4d3K. \n\nWe covered 22% of the Initial sky localization area (Bayestar, GCN 42650 LVK collaboration) and 16% of the Updated sky localization area (Bilby, GCN 2690, LVK collaboration). Preliminary analysis did not reveal any clear candidate that can be associated to the event (with limit magnitudes ranging from 17 to 21 mag in r-band at 5 sigma). We re-conducted a second epoch of observations the day after.\n\nAll the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2025). Images obtained were calibrated using the PanSTARRS DR1 catalog.\n\nWe are currently investigating candidates reported by other collaborations.\n\nGRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).\n",
"published": "2025-11-15T22:38:45.158779Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-15T22:38:45.158801Z",
"modified": "2025-11-15T22:38:45.164927Z",
"targets": []
},
{
"id": 5798761,
"topic": "gcn.circulars",
"uuid": "5ba9af93-ed67-473c-af12-74228dcf7934",
"title": "LIGO/Virgo/KAGRA S251112cm: AT2025adht follow-up at Maidanak observatory by GRANDMA",
"submitter": "Yodgor Rajabov at UBAI <rajabov@astrin.uz>",
"authors": "Yodgor Rajabov at UBAI <rajabov@astrin.uz>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42698"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: AT2025adht follow-up at Maidanak observatory by GRANDMA",
"createdOn": 1763214843900,
"submitter": "Yodgor Rajabov at UBAI <rajabov@astrin.uz>",
"circularId": 42698,
"submittedHow": "web"
},
"message_text": "O. Burkhonov, Y. Rajabov, Y. Tillayev (UBAI), P. Hello (IJCLAB), A. Klotz (IRAP), M. Coughlin (UMN), S. Karpov (FZU), M. Pillas (IAP), M. Mazek (FZU ), S. Antier (IJCLAB), O. Pyshna (Caltech) on behalf of GRANDMA:\n\nWe detected transient event 2025adht in RA_J2000=12:00:24.3431, Dec_J2000=+49:02:51.7 reported by (GCN 42677 Anand et al., Franz GCN 42675 et al.,). Observations were carried out at the 1.5-meter telescope Maidanak Observatory by using 4Kx4K SNUCAM CCD. All observations were taken using a Bessel R filter. The observations started at 2025-11-15T00:13:15 UTC and ended at 2025-11-15T00:40:17 UTC. A total of 6 CCD images with an exposure of 300 seconds were obtained.\n\nDespite the fact that this object is located far from the equator, we checked for the presence of small bodies in this region using the small body database from 14 November 2025. The check was negative. Cross-identification results indicated the same galaxy without any transient events: DSS J120024.56+490254.3, WISEA J120024.53+490254.1, and GALEXASC J120024.49+490252.9.\nWe analyzed our data using our standard pipeline and with STDWeb/STDPipe (Karpov, 2025). We present stacked results after galaxy soustraction.\n \n MJD | DATE-OBS | MAG |M_ERR|U.L.|FILTER| Telescope| MAG system\n--------------------------------------------------------------------------------------\n60994.00920139 | 2025-11-15 00:29 | 21.54|0.1|22.10|R|UBAI/AZT-22|Vega, Gaia DR3\n\nWhich has an equivalent using PS1 of 21.64+/- 0.1 in sdssr using PS1 (color term 0.13).\n\nMore observations are planned.\n \nGRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/)",
"published": "2025-11-15T13:54:13.309541Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-15T13:54:13.309561Z",
"modified": "2025-11-15T13:54:13.378632Z",
"targets": []
},
{
"id": 5798655,
"topic": "gcn.circulars",
"uuid": "1ddb6dce-c6ab-46b4-a6da-f12f45875c78",
"title": "LIGO/Virgo/KAGRA S251112cm: NED Galaxies in the 4-Update Localization Volume",
"submitter": "David Cook at Caltech/IPAC-NED <dcook@ipac.caltech.edu>",
"authors": "David Cook at Caltech/IPAC-NED <dcook@ipac.caltech.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42693"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: NED Galaxies in the 4-Update Localization Volume",
"createdOn": 1763178416572,
"submitter": "David Cook at Caltech/IPAC-NED <dcook@ipac.caltech.edu>",
"circularId": 42693,
"submittedHow": "web"
},
"message_text": "David O. Cook (Caltech/IPAC), Rick Ebert (Caltech/IPAC), George Helou (Caltech/IPAC), Joseph M. Mazzarella (Caltech/IPAC), Marion Schmitz (Caltech/IPAC), and Leo Singer (NASA/GSFC)\n\nOn behalf of the NASA/IPAC Extragalactic Database (NED) Team.\n\nWe spatially cross-matched the LVK S251112cm-4-Update sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023; https://ned.ipac.caltech.edu/NED::LVS/) which is a subset of NED with a redshift or redshift-independent distance less than 1000 Mpc. We find 9047 galaxies within the 90% containment volume, and we list here the top 20 galaxies sorted by the joint probability of the 3D localization and the WISE W1 luminosity (an observable proxy for stellar mass). For the full or top 20 list of galaxies in the 90% volume go either to the NED Gravitational Wave Followup service at https://ned.ipac.caltech.edu/uri/NED::GWF/ or click on the following links:\n\nFull List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S251112cm/4 \nTop 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S251112cm/4/20\n\nThe NED-GWF service provides downloadable galaxy lists and visualizations for candidate host galaxies. For each GW alert, these products are automatically generated and made available within minutes to expedite efficient electromagnetic follow-up observations. The NED top 20 list is sorted by the joint probability of the 3D localization and the WISE W1 luminosity, but users can sort on additional pre-computed prioritization metrics (star formation rate, P_3D * P_SFR; and specific star formation rate, P_3D * P_sSFR; etc.) which are available via downloading the entire galaxy list inside the event's probability volume.\n\n| objname| ra| dec|objtype| DistMpc|DistMpc_unc| m_NUV| m_NUV_unc| m_Ks| m_Ks_unc| m_W1| m_W1_unc| P_3D|P_3D_LumW1|\n|-------------------------|--------------|--------------|-------|-----------|-----------|------------|------------|------------|------------|------------|------------|--------|----------|\n| IC 1633| 17.48145| -45.93116| G| 96.06| 3.43| null| null| 8.396| 0.025| 8.999| 0.006|8.02e-06| 1.10e-08|\n| IC 0564| 146.58792| 3.07130| G| 75.75| 2.62| null| null| 10.033| 0.035| 10.010| 0.006|2.41e-05| 8.10e-09|\n| IC 1464B| 345.79587| -8.98909| G| 105.88| 0.59| null| null| 10.015| 0.036| 9.741| 0.006|8.31e-06| 6.98e-09|\n|WISEA J100012.04+093856.0| 150.05020| 9.64890| G| 78.82| 0.30| null| null| 11.073| 0.096| 10.233| 0.006|2.04e-05| 6.04e-09|\n| UGC 05226| 146.51479| 4.40348| G| 66.86| 15.78| 18.763| 0.092| 10.211| 0.041| 10.083| 0.089|2.21e-05| 5.42e-09|\n| ESO 197- G 021| 31.13585| -52.17213| G| 87.54| 0.39| null| null| 9.099| 0.026| 9.375| 0.006|6.49e-06| 5.21e-09|\n| MCG -01-24-010| 140.09147| -7.88074| G| 53.94| 2.54| 15.885| 0.007| 10.054| 0.032| 9.821| 0.030|2.49e-05| 5.05e-09|\n| MRK 0421| 166.11381| 38.20883| G| 85.15| 33.84| null| null| 9.996| 0.029| 9.258| 0.005|5.81e-06| 4.92e-09|\n| IC 1464A| 345.80030| -8.99285| G| 107.09| 0.04| null| null| 11.963| 0.011| 10.070| 0.006|7.57e-06| 4.81e-09|\n| NGC 7364| 341.10153| -0.16213| G| 76.48| 8.25| 16.366| 0.001| 9.478| 0.028| 9.218| 0.003|6.74e-06| 4.80e-09|\n| IC 1471| 347.18676| -12.63948| G| 83.00| 17.58| 17.246| 0.027| 10.334| 0.035| 10.290| 0.006|1.49e-05| 4.63e-09|\n| ESO 243- G 051| 17.83050| -45.93204| G| 94.78| 0.36| 17.032| 0.008| 10.015| 0.031| 10.036| 0.006|8.85e-06| 4.53e-09|\n| NGC 2951 NED01| 144.92019| -0.23515| G| 70.23| 0.53| 18.380| 0.003| 10.498| 0.057| 10.537| 0.004|2.33e-05| 4.19e-09|\n| IC 2471| 141.30071| -6.82994| G| 58.50| 12.39| 18.644| 0.054| 9.949| 0.034| 10.076| 0.006|2.19e-05| 4.12e-09|\n| NGC 3070| 149.52893| 10.35980| G| 60.25| 5.89| 18.225| 0.068| 9.260| 0.030| 9.503| 0.006|1.21e-05| 4.12e-09|\n| ESO 197- G 018| 30.62846| -50.93160| G| 110.00| 24.82| null| null| 9.612| 0.028| 9.779| 0.006|4.35e-06| 3.80e-09|\n| NGC 2951 NED02| 144.91664| -0.23524| G| 71.31| 0.04| 18.383| 0.003| 12.873| 0.052| 10.592| 0.004|2.13e-05| 3.75e-09|\n| ESO 243- G 045| 17.26888| -45.77349| G| 82.00| 9.44| 18.245| 0.024| 9.713| 0.035| 9.964| 0.006|9.07e-06| 3.71e-09|\n| IC 0563| 146.58473| 3.04574| G| 57.00| 22.05| 16.948| 0.010| 10.810| 0.054| 10.328| 0.027|2.54e-05| 3.62e-09|\n| ESO 197- G 010| 28.30237| -49.56039| G| 76.43| 6.54| null| null| 8.882| 0.034| 9.458| 0.006|6.17e-06| 3.50e-09|\n\nTable 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S251112cm sorted by the joint probability of 3D position and WISE W1 luminosity (P_3D * P_LumW1). Galaxy is the NED preferred name. RA and Dec are the Equatorial coordinates in degrees (J2000). Objtype is the object type of the galaxy candidate. Distance is the distance to the galaxy in Mpc. m_NUV and mErr_NUV are the apparent magnitude and error from GALEX. m_Ks and mErr_Ks are the apparent magnitude and error from 2MASS. m_W1 and mErr_W1 are the apparent magnitude and error from AllWISE. P_3D is the probability that the galaxy is in the volume given the distance of GW event. P_3D_LumW1 is the joint probability within the volume weighted by the WISE1 luminosity of the galaxy (P_3D * P_LumW1). \n",
"published": "2025-11-15T03:47:02.586680Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-15T03:47:02.586698Z",
"modified": "2025-11-15T03:47:02.595601Z",
"targets": []
},
{
"id": 5798646,
"topic": "gcn.circulars",
"uuid": "681c9567-a9b0-4088-9639-1ed184fc3252",
"title": "LIGO/Virgo/KAGRA S251112cm: DECam GW-MMADS candidates",
"submitter": "Xander J Hall at Carnegie Mellon University <xjh@andrew.cmu.edu>",
"authors": "Xander J Hall at Carnegie Mellon University <xjh@andrew.cmu.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42691"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: DECam GW-MMADS candidates",
"createdOn": 1763176595431,
"submitter": "Xander J Hall at Carnegie Mellon University <xjh@andrew.cmu.edu>",
"circularId": 42691,
"submittedHow": "web"
},
"message_text": "Xander J. Hall (CMU), Tomás Cabrera (CMU), Julius Gassert (CMU/LMU), Lei Hu (UPenn), Antonella Palmese (CMU), Brendan O’Connor (CMU), Igor Andreoni (UNC), on behalf of the Gravitational Wave MultiMessenger Astronomy DECam Survey (GW-MMADS) team report:\n\nWe observed the high probability area of the LVK gravitational wave candidate S251112cm (GCN 42650) using the wide-field Dark Energy Camera (DECam) on the 4m Blanco telescope. Observations started at 2025-11-14 00:03 UTC (Prop ID: 2023B-851374; PI Palmese & Andreoni) and focused on the southern lobe of the Bilby skymap (GCN 42690; 30% of the total posterior probability).\n\nWe run the SFFT difference imaging (Hu et al. 2022) on the available images, filter out likely stars and moving objects, and then visually inspect the remaining transients. We report on TNS 54 new transients within the observed area, and we report here select transients:\n\n| id | AT name | ra | dec | discovery_date (UT) | mag_g | mag_g_err | mag_g-mag_i | NED separation |\n| ------------------------ | ---------- | ---------- | ---------- | ----------------------- | ------ | ----- | ----- | ----- |\n| T202511140018095m335115* | AT 2025adjp | 4.539622 | -33.854284 | 2025-11-14 02:08:26.016 | 21.13 | 0.04 | 0.25 | 92.7\", 94.5\", 94.6\"\n| T202511140030086m410443 | AT 2025adkl | 7.535766 | -41.078709 | 2025-11-14 02:13:43.104 | 20.91 | 0.03 | -0.14 | 90.5\"\n\n*This transient is within 2' of three NED in-volume galaxies.\n\nWe note while both of these transients are within 2' of a NED in-volume galaxy (GCN 42653), they are both near galaxies with LS DR9 photo-z > 0.12 which would place them outside of the volume. \n\nFurther analysis is underway.\n\nWe thank the CTIO and NOIRLab staff for supporting these observations and the data calibration.",
"published": "2025-11-15T03:16:41.642709Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-15T03:16:41.642732Z",
"modified": "2025-11-15T03:16:41.740734Z",
"targets": []
},
{
"id": 5798174,
"topic": "gcn.circulars",
"uuid": "7e812629-daa7-4150-881b-5be9389a208e",
"title": "LIGO/Virgo/KAGRA S251112cm: Updated Sky localization and false alarm rate estimate",
"submitter": "Colm Talbot at Princeton University <talbotcolm@gmail.com>",
"authors": "Colm Talbot at Princeton University <talbotcolm@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42690"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Updated Sky localization and false alarm rate estimate",
"createdOn": 1763167289305,
"submitter": "Colm Talbot at Princeton University <talbotcolm@gmail.com>",
"circularId": 42690,
"submittedHow": "web"
},
"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S251112cm (GCN Circular 42650). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,1, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:\n\nhttps://gracedb.ligo.org/superevents/S251112cm\n\nFor the Bilby.multiorder.fits,1 sky map, the 90% credible region is 1681 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 93 +/- 27 Mpc (a posteriori mean +/- standard deviation).\n\nThe false alarm rate, as estimated by the MBTA SSM analysis pipeline with an updated background model, has been updated to about one in 4 years.\n\nThe online search for sub-solar-mass regions is covered by two independent pipelines: MBTA SSM and GstLAL SSM [2]. For the parameter space relevant to the present candidate, only MBTA SSM provides online coverage; therefore, the candidate was triggered solely by MBTA SSM.\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040\n\n [2] https://emfollow.docs.ligo.org/userguide/analysis/index.html#false-alarm-rate-for-alerts-and-trials-factor",
"published": "2025-11-15T00:41:38.351117Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-15T00:41:38.351137Z",
"modified": "2025-11-15T00:41:38.363967Z",
"targets": []
},
{
"id": 5796255,
"topic": "gcn.circulars",
"uuid": "14bd98d5-7440-4dc2-839f-b13fa85b5bfd",
"title": "LIGO/Virgo/KAGRA S251112cm: ATLAS targeted observations of the skymap",
"submitter": "Adam Smith at Queen's University Belfast <asmith67@qub.ac.uk>",
"authors": "Adam Smith at Queen's University Belfast <asmith67@qub.ac.uk>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42682"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: ATLAS targeted observations of the skymap",
"createdOn": 1763135960573,
"submitter": "Adam Smith at Queen's University Belfast <asmith67@qub.ac.uk>",
"circularId": 42682,
"submittedHow": "web"
},
"message_text": "A. Smith, M. Nicholl, (QUB), J. Gillanders, S. J. Smart, K. W. Smith, (Oxford), D. R. Young, C. R. Angus, M. D. Fulton, T. Moore, A. Aamer, S. Sim, J. Weston, X. Sheng, D. Magill, P. Ramsden (QUB), S. Srivastav, H. Stevance, F. Stoppa, A. Cooper, J. Tweddle, L. Eastman (Oxford), L. Shingles (GSI/QUB), L. Rhodes (TSI/McGill), L. Denneau, J. Tonry, H. Weiland, R. Siverd (IfA, University of Hawaii), N. Erasmus, W. Koorts (South African Astronomical Observatory), A. Rest (STScI), T.-W. Chen (NCU), C. Stubbs (Harvard), J. Sommer (LMU/QUB), B. Schmidt (ANU):\n\n\nWe report observations of the Bilby.fits skymap of the compact binary merger candidate S251112cm (The LIGO-Virgo-Kagra Collaboration, GCN 42650) with the ATLAS telescope system (Tonry et al., 2018, PASP, 13, 164505). ATLAS is a quintuple 0.5m optical telescope survey system (Hawaii x 2, South Africa, Chile, Tenerife) employing three filters, cyan, orange, and ‘clear’. In our primary NASA mission for Near-Earth Object discovery, we cover the entire visible night sky every 24hrs to AB magnitude depths m ~ 19.5, weather and Moon permitting.\n\nDuring focused science operations, we covered part of the accessible skymap of S251112cm. A sequence of quads (4 x 120-sec images) was taken at each pointing position. The images were processed with the ATLAS pipeline, and reference images were subtracted from each one. Transient candidates were identified and run through our standard filtering procedures (Smith et al., 2020, PASP, 132, 1). We covered 665.14 square degrees of the bilby.fits skymap 90% area, and covered a sky region totalling 45.08% of the event's full localisation likelihood, South of declination = 11 degrees. Data acquisition began at MJD 60991.811354 or 2025-11-12 19:28:20 (UTC), 3.5hrs after the LVC Preliminary/Initial notice and 4.2hrs after the merger event at 2025-11-12 15:18:45.362 (UTC).\n\nObservations lasted between ~4.2hrs to 41.3hrs after the GW detection. The depths of our images typically reached m_o < 19.5 AB mag. We found 26 transient sources, including 5 previously unreported transients. However, all had been previously detected by ATLAS before the merger event, or reported to the IAU Transient name server (https://www.wis-tns.org) and/or are associated with host galaxies with photometric redshifts beyond z > 0.05. We are reporting all discoveries to the TNS, where they can be tracked, classified, searched, and commented upon. We encourage further information to be reported on the TNS object pages. \n\nWe checked the ATLAS forced photometry for the 3 GOTO objects reported by Ackley et al. (GCN 42658), and confirmed that all three have flux detected before the S251112cm GW event time. This flux on the individual 30 sec images are each below 5-sigma significance but the combined detections over multiple nights indicate the source was detected. These detections can be checked on ATLAS forced photometry server (Shingles et al. AstroNote 2021-7). \n\nThe Asteroid Terrestrial-impact Last Alert System (ATLAS) project is primarily funded to search for Near-Earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, the University of Oxford, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile.\n",
"published": "2025-11-14T15:59:30.198504Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-14T15:59:30.198524Z",
"modified": "2025-11-14T15:59:30.214698Z",
"targets": []
},
{
"id": 5796089,
"topic": "gcn.circulars",
"uuid": "d2bc40ab-2193-43fb-a01d-c2499a959138",
"title": "LIGO/Virgo/KAGRA S251112cm: Swift XRT observations, 20 X-ray sources",
"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/42681"
},
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Swift XRT observations, 20 X-ray sources",
"createdOn": 1763133333584,
"submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
"circularId": 42681,
"submittedHow": "email"
},
"message_text": "K.L. Page (U. Leicester), P.A. Evans (U. Leicester), J.A. Kennea (PSU), A.\nTohuvavohu (Cosmic Frontier Labs), S.B. Cenko (NASA/GSFC), R.A.J. Eyles-Ferris (U.\nLeicester), A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), A.A. Breeveld\n(UCL-MSSL), S. Campana (INAF-OAB), J.J. Delaunay (PSU), M. De Pasquale (University\nof Messina), S. Dichiara (PSU), P. D’Avanzo (INAF-OAB), A. D’Aì (INAF-IASFPA) ,\nV. D’Elia (ASI-SSDC & INAF-OAR), C. Gronwall (PSU), D. Hartmann (Clemson\nUniversity), N. Klingler (NASA-GSFC / UMBC / CRESST II), N.P.M. Kuin (UCL-MSSL), S.\nLaha (NASA/GSFC), S.R. Oates (U. Birmingham), J.P. Osborne (U. Leicester), P.\nO’Brien (U. Leicester), M.J. Page (UCL-MSSL), G. Raman (PSU) S. Ronchini (PSU), T.\nSbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.H. Siegel (PSU), G. Tagliaferri\n(INAF-OAB), E. Troja (U Tor Vergata, INAF) report on behalf of the Swift team:\n\nSwift has carried out 105 observations of the LVK error region for the GW trigger\nS251112cm convolved with the 2MPZ catalogue (Bilicki et al. 2014, ApJS, 210, 9),\nusing the 'BAYESTAR' (version BAYESTAR.fits.gz) GW localisation map. As this is a 3D\nskymap, galaxy distances were taken into account in selecting which ones to observe.\nThe observations currently span from 7.6 ks to 117 ks after the LVK trigger, and the\nXRT has covered 12.7 deg^2 on the sky (corrected for overlaps). This covers 1.3% of\nthe probability in the 'BAYESTAR' (version BAYESTAR.fits.gz) skymap, and 20% after\nconvolving with the 2MPZ galaxy catalogue, as described by Evans et al. (2016,\nMNRAS,\t462, 1591).\n\nWe have detected 20 X-ray sources. Each source is assigned a rank of 1-4 which\ndescribes how likely it is to be related to the GW trigger, with 1 being the most\nlikely and 4 being the least likely. The ranks are described at\nhttps://www.swift.ac.uk/ranks.php.\n\nWe have found:\n\n * 0 sources of rank 1\n * 0 sources of rank 2\n * 7 sources of rank 3\n * 13 sources of rank 4\n\n\nRANK 3 sources\n==============\n\nThese are uncatalogued X-ray sources, however they are not brighter than previous\nupper limits, so do not stand out as likely counterparts to the GW trigger.\n\n| Source ID\t | RA\t\t | Dec \t | Err90 | Detection Flag\t|\n| S251112cm_X1 | 11 09 55.90 | +36 08 20.7 |\t8.0\" |\t\t POOR |\n| S251112cm_X38 | 23 47 03.18 | -28 07 08.2 |\t9.5\" |\t\t POOR |\n| S251112cm_X53 | 11 08 18.65 | +36 11 04.6 |\t8.1\" |\t\t POOR |\n| S251112cm_X72 | 12 22 09.27 | +55 52 20.4 |\t5.9\" |\t\t GOOD |\n| S251112cm_X73 | 01 08 29.26 | -46 59 48.1 |\t8.9\" |\t\t POOR |\n| S251112cm_X78 | 23 48 35.23 | -28 14 05.5 |\t9.8\" |\t\t POOR |\n| S251112cm_X79 | 23 48 06.04 | -28 04 35.1 | 12.3\" |\t\t POOR |\n\n\nRANK 4 sources\n==============\n\nThese are catalogued X-ray sources, showing no signs of outburst compared to\nprevious observations, so they are not likely to be related to the GW trigger.\n\n| Source ID\t | RA\t\t | Dec \t | Err90 | Detection Flag\t|\n| S251112cm_X2 | 11 12 06.93 | +35 27 45.6 |\t6.8\" |\t\t GOOD |\n| S251112cm_X3 | 09 20 46.26 | -08 03 21.4 |\t5.5\" |\t\t GOOD |\n| S251112cm_X5 | 23 51 37.99 | -28 18 18.1 |\t7.6\" |\t\t POOR |\n| S251112cm_X50 | 11 37 24.49 | +47 27 44.7 |\t7.4\" |\t\t GOOD |\n| S251112cm_X51 | 01 08 20.79 | -47 07 36.3 |\t7.4\" |\t\t POOR |\n| S251112cm_X52 | 01 07 42.60 | -46 54 24.5 |\t6.1\" |\t\t GOOD |\n| S251112cm_X67 | 11 11 04.66 | +35 13 59.3 |\t6.9\" |\t\t GOOD |\n| S251112cm_X68 | 22 44 47.97 | -00 06 17.5 |\t8.8\" |\t\t GOOD |\n| S251112cm_X69 | 02 36 19.70 | -54 51 50.8 |\t5.8\" |\t\t GOOD |\n| S251112cm_X70 | 13 06 57.05 | +59 58 48.1 | 10.7\" |\t REASONABLE |\n| S251112cm_X71 | 12 23 00.00 | +55 40 04.4 |\t5.1\" |\t\t GOOD |\n| S251112cm_X87 | 11 12 01.25 | +37 58 26.3 |\t6.1\" |\t\t GOOD |\n| S251112cm_X88 | 11 04 27.52 | +38 12 36.6 |\t3.5\" |\t\t GOOD |\n\nFor all flux conversions and comparisons with catalogues and upper limits from other\nmissions, we assumed a power-law spectrum with NH=3x10^20 cm^-2, and photon index\n(Gamma)=1.7, unless otherwise stated.\n\nThe results of the XRT automated analysis, including details of the sources listed\nabove, are online at https://www.swift.ac.uk/LVC/S251112cm\n\nThis circular is an official product of the Swift XRT team.\n\n\n",
"published": "2025-11-14T15:15:42.417254Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-14T15:15:42.417275Z",
"modified": "2025-11-14T15:15:42.426741Z",
"targets": []
},
{
"id": 5795879,
"topic": "gcn.circulars",
"uuid": "10b4ad21-06a4-434c-aaa9-3fc17115989a",
"title": "LIGO/Virgo/KAGRA S251112cm: Candidates from the Zwicky Transient Facility",
"submitter": "Shreya Anand <shreyasahasram08@gmail.com>",
"authors": "Shreya Anand <shreyasahasram08@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42677"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Candidates from the Zwicky Transient Facility",
"createdOn": 1763086819370,
"submitter": "Shreya Anand <shreyasahasram08@gmail.com>",
"circularId": 42677,
"submittedHow": "web"
},
"message_text": "S. Anand (Stanford), R. Stein (UMD), X. J. Hall (CMU), V. Swain (IIT-B), A. Saikia (IIT-B), T. Mohan (IIT-B), V. Bhalerao (IIT-B), D. Cook (Caltech/IPAC), A. Singh (SU), M. M. Kasliwal (Caltech), E. C. Bellm (UW), M. Coughlin (UMN), T. du Laz (Caltech), V. Karambelkar (Columbia), G. Waratkar (Caltech), I. Andreoni (UNC), A. Palmese (CMU) report,\n\non behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: \n\nWe observed the localization region of the LVK sub-solar mass candidate S251112cm (GCN 42650) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2025-11-12 09:21 UTC, approximately 18 hours after merger, covering 38.3% of the probability within the 90% credible region of the LVK skymap in g- and r-bands. This estimate accounts for chip gaps. Each exposure was 300s with a median r-band depth of 21.14 mag. \n \nThe images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019), removing candidates with history of variability prior to the merger time. \n\nBecause of the nature of the GW trigger as a sub-solar mass merger candidate, we do not exclude any candidates that may be consistent with being young stripped envelope supernovae (SESNe). Disk fragmentation or core fissioning in SESNe may lead to the formation of subsolar mass neutron stars (Metzger et al. 2024, Kasliwal et al. 2025).\n\nAfter filtering, 8 transient candidates remain, all within the 95.0% localization of the skymap. Candidates marked as FAR have redshifts from Legacy Survey or from SDSS (shown below). Redshift lower limits come from Legacy Survey (l95; a conservative lower limit on the photometric redshift). We list the 8 candidates found in the table below: \n\n| ZTF Name | RA (deg) | DEC (deg) | MJD | Filt | Mag | MagErr | Redshift | Note |\n| ------------- | ---------- | --------- | -------- | ---- | ----- | ------ | --------------------------------------- | ---------------------------------------- |\n| ZTF25aceekrn* | 180.101460 | 49.047764 | 60992.43 | g | 21.04 | 0.22 | photo-z=0.14 (LS); photo-z=0.189 (SDSS) | FAR |\n| ZTF25aceekwp | 181.804049 | 55.653636 | 60992.44 | g | 21.23 | 0.20 | photo-z>0.24 (LS) | FAR |\n| ZTF25aceelgz | 190.811137 | 57.328886 | 60992.47 | g | 21.15 | 0.13 | spec-z=0.476 (SDSS) | AGN-like; w1-w2=0.97 |\n| ZTF25aceelbm | 169.544486 | 41.094776 | 60992.41 | g | 21.20 | 0.23 | photo-z=0.21 (LS); photo-z=0.24 (SDSS) | FAR |\n| ZTF25aceemla | 185.395941 | 56.586289 | 60992.46 | r | 21.25 | 0.23 | photo-z>0.28 (LS) | FAR |\n| ZTF25aceekzz | 169.076786 | 39.863435 | 60992.41 | g | 21.32 | 0.26 | photo-z=0.528 (LS) | AGN-like; ZTF pre-detections; w1-w2=1.13 |\n| ZTF25aceelmh | 184.916369 | 57.167778 | 60992.47 | g | 21.61 | 0.22 | photo-z>0.41 (LS); photo-z=0.42 (SDSS) | FAR |\n| ZTF25aceempu | 169.569004 | 35.985827 | 60992.49 | r | 21.60 | 0.21 | photo-z>0.23 (LS) | FAR |\n\n*ZTF25aceekrn (AT 2025adht) was previously reported by the TROVE team (GCN 42675) with a photo-z=0.11 +/- 0.07 (nominally consistent with the LVK distance posterior). A spectrum can help resolve this discrepancy.\n\nNone of the other candidates reported here warrant additional follow-up.\n\nAll candidates have been reported to the Transient Name Server, and some are pending assignment of a TNS name. \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. GROWTH acknowledges the generous support of the NSF under PIRE Grant No 1545949. Alert database searches are done by AMPEL (Nordin et al. 2019) and Kowalski (Duev et al. 2019). The GROWTH India Telescope (GIT, Kumar et al., 2022) is set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. Its operations are partially supported by funding from the IIT Bombay alumni batch of 1994. The Fritz and SkyPortal projects acknowledge the generous support of The Gordon and Betty Moore Foundation.",
"published": "2025-11-14T02:20:27.724482Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-14T02:20:27.724515Z",
"modified": "2025-11-14T02:20:27.731153Z",
"targets": []
},
{
"id": 5795812,
"topic": "gcn.circulars",
"uuid": "49404912-3838-4cfd-a8b1-7cb7cb122fad",
"title": "LIGO/Virgo/KAGRA S251112cm: TROVE Vetting of TNS Candidates",
"submitter": "Noah Franz at University of Arizona/Steward Observatory <noahfranz13@gmail.com>",
"authors": "Noah Franz at University of Arizona/Steward Observatory <noahfranz13@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42675"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: TROVE Vetting of TNS Candidates",
"createdOn": 1763073011684,
"submitter": "Noah Franz at University of Arizona/Steward Observatory <noahfranz13@gmail.com>",
"circularId": 42675,
"submittedHow": "web"
},
"message_text": "N. Franz (U. Arizona), N. Vieira (Northwestern), C. D. Kilpatrick (Northwestern), D. J. Sand (U. Arizona), B. Subrayan (U. Arizona), G. Hosseinzadeh (UC San Diego), M. Shrestha (Monash U), K. D. Alexander (U. Arizona), W. Fong (Northwestern), report on behalf of the TROVE collaboration:\n\nWe analyzed candidate counterparts to the LIGO/Virgo/KAGRA (LVK) gravitational wave event S251112cm (GCN 42650) using the Multi-messenger Tool for Rapid Object Vetting and Examination (TROVE). We searched within the 95th percentile localization region for candidate optical counterparts in host galaxies at the approximate luminosity distance of S251112cm. We further crossmatch to minor planet and point source catalogs and rule out sources that do not appear photometrically similar to kilonova light curves. For additional details, see the vetting procedures described in N. Franz, et al., 2025, arXiv:2510.17104.\n\nBelow, we report all candidates that remain viable after running our vetting procedure using publicly available information on all publicly reported sources, to date, on the Transient Name Server (TNS). We include their TNS identifier, coordinates, cumulative probability at the coordinate location in the latest LVK map, most likely host redshift, most recent magnitude, and the initial reporting group. Candidates are ranked using a scoring procedure designed to identify kilonova counterparts to GW events (N. Franz, et al., 2025, arXiv:2510.17104). The reported candidates are not clearly identified as kilonovae, but we note that the progenitor system of S251112cm is poorly constrained given the exceptional attributes of the event as reported by LIGO: a probability of the system containing a neutron star < 8%, probability of containing a sub-solar mass object >99%, and a chirp mass in the range 0.1 to 0.87 solar masses.\n\n\n| TNS Name | RA [HMS] | Dec [DMS] | Localization Probability Contour | Most likely Host-z | Most recent public magnitude | Discovery Survey | Comments |\n| ------- | ------ | ------- | ------- | ------- | ------- | ------- | ------- |\n| AT2025adht | 12:00:24.350 |+49:02:51.95 | 0.83 | 0.11 +/- 0.07 (photo-z) | g=21.4 +/- 0.2 | ZTF | |\n| AT2025adgp | 01:47:46.202 | -51:49:25.52 | 0.20 | 0.06 +/- 0.02 (photo-z) | o=19.1 +/- 0.05 | BlackGEM | ATLAS pre-detection ~6 hours before S251112cm. This candidate was initially presented in GCN42663 and the ATLAS pre-detections were noted in GCN 42666. |\n| AT2025adhf | 02:43:44.411 | -55:19:06.44 | 0.15 | 0.11 +/- 0.02 (photo-z) | o=19.22 +/- 0.05 | ATLAS | ATLAS pre-detections in the ~week leading up to S251112cm. |\n| AT2025adhs | 04:12:56.396 | -54:11:46.41 | 0.09 | 0.04 (spec-z) | o=20.71 +/- 0.22 | BlackGEM | |\n\nWe encourage additional follow up of these candidates to determine whether they remain viable counterparts to S251112cm. We note that there are 10 other transients reported to the TNS in the 95% localization region that we rule out for other reasons (e.g., excessive pre-detections, incorrect host distance as compared to S251112cm, etc.): AT2025adhj, AT2025addc, AT2025adhr, AT2025adhu, AT2025adhg, AT2025addb, AT2025adhh, AT2025adda, AT2025adhe, AT2025adgq.",
"published": "2025-11-13T22:30:19.820529Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-13T22:30:19.820550Z",
"modified": "2025-11-13T22:30:19.848475Z",
"targets": []
},
{
"id": 5795773,
"topic": "gcn.circulars",
"uuid": "5a03d48a-1175-4867-8570-005baa0e34a2",
"title": "LIGO/Virgo/KAGRA S251112cm: FTW observations of galaxies within localization region",
"submitter": "Julius Gassert at Ludwig-Maximilians-Universität München <julius.gassert@campus.lmu.de>",
"authors": "Julius Gassert at Ludwig-Maximilians-Universität München <julius.gassert@campus.lmu.de>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42674"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v6.0.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: FTW observations of galaxies within localization region",
"createdOn": 1763064743669,
"submitter": "Julius Gassert at Ludwig-Maximilians-Universität München <julius.gassert@campus.lmu.de>",
"circularId": 42674,
"submittedHow": "web"
},
"message_text": "Julius Gassert (CMU/LMU), Malte Busmann (LMU), Xander J. Hall (CMU), Brendan O’Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report:\n\nWe observed a sample of 19 DESI galaxies, ranked by 3D position and brightness following the methodology laid out in Hall et al. (2025), in the sky localization region of gravitational wave event S251112cm (GCN 42650) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J bands simultaneously. Observations started at 2025-11-12T17:43 (UT). Typical three-sigma limits for point sources are r, i ~ 21, and the field of view is 7’x7’. We do not identify any candidate GW counterpart in difference imaging with respect to Legacy Survey and PS1 data. The coordinates of the observed targets are listed below.\n\n| R.A. | dec |\n|---|---|\n| 164.426910134 | 37.65453732955 |\n| 165.5240393492 | 38.78722513647 |\n| 167.4811243685 | 36.94655132258 |\n| 173.5605908567 | 49.0431665104 |\n| 182.4385674509 | 56.52359456357 |\n| 182.8894005861 | 57.73745323273 |\n| 186.0084874694 | 58.38519262405 |\n| 196.9032263873 | 60.15719529696 |\n| 197.1937364898 | 62.27166824173 |\n| 250.834423606 | 70.63254712505 |\n| 341.1015299287 | -0.162034769873 |\n| 341.5808358893 | 3.210042314846 |\n| 343.2053071078 | 1.201113639068 |\n| 344.2120066199 | -8.967554297055 |\n| 344.5092848207 | -3.76968999454 |\n| 345.0369565289 | -12.80783236183 |\n| 346.7423345683 | -9.286127524436 |\n| 347.1867614296 | -12.63952485965 |\n| 349.7190055484 | -10.25928200595 |\n\nWe thank Christoph Ries from the Wendelstein Observatory staff for obtaining these observations.",
"published": "2025-11-13T20:12:32.694619Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-13T20:12:32.694647Z",
"modified": "2025-11-13T20:12:32.705777Z",
"targets": []
},
{
"id": 5795612,
"topic": "gcn.circulars",
"uuid": "e7beda2b-6843-45f2-b95c-517b70f1939d",
"title": "LIGO/Virgo/KAGRA S251112cm: ATLAS pre-detections of AT2025adgp and AT2025adgq",
"submitter": "James Gillanders at University of Oxford <jhgillanders.astro@gmail.com>",
"authors": "James Gillanders at University of Oxford <jhgillanders.astro@gmail.com>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42666"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: ATLAS pre-detections of AT2025adgp and AT2025adgq",
"createdOn": 1763035943691,
"submitter": "James Gillanders at University of Oxford <jhgillanders.astro@gmail.com>",
"circularId": 42666,
"submittedHow": "web"
},
"message_text": "J. H. Gillanders (Oxford), S. J. Smartt, K. W. Smith (Oxford/QUB), S. Srivastav, H. Stevance, F. Stoppa, A. Cooper (Oxford), M. Nicholl, D. R. Young, C. R. Angus, M. D. Fulton, T. Moore, A. Aamer, M. McCollum, S. Sim, J. Weston, X. Sheng, D. Magill, P. Ramsden (QUB), L. Shingles (GSI/QUB), L. Rhodes (TSI/McGill), L. Denneau, J. Tonry, H. Weiland, R. Siverd (IfA, University of Hawaii), N. Erasmus, W. Koorts (South African Astronomical Observatory), A. Rest (STScI), T.-W. Chen (NCU), C. Stubbs (Harvard), J. Sommer (LMU/QUB), B. Schmidt (ANU):\n\nWe are currently observing the skymap of the LIGO/Virgo/KAGRA GW event S251112cm (LVK Collaboration, GCN 42650) with ATLAS (Tonry et al., 2018, PASP, 13, 164505; Licandro et al., 2023, arXiv:2302.07954). ATLAS is a quintuple 0.5-m optical telescope survey system (Hawaii x2, South Africa, Chile, Tenerife) employing three filters, cyan, orange and ‘clear’. In our primary NASA mission for Near-Earth Object discovery, we cover the entire visible night sky every 24 hours to a magnitude depth of m ~ 19.5, weather and Moon permitting. We will report our candidate discoveries in an upcoming GCN.\n\nGroot et al. (GCN 42663) report on BlackGEM/MeerLICHT observations of the GW skymap of S251112cm (GCN 42650), and they present two candidate counterparts: AT2025adgp and AT2025adgq. \n\nHere, we note that both AT2025adgp and AT2025adgq have historical detections in ATLAS, which precede the GW detection. The public ATLAS data (for these and any other transient) are accessible through the ATLAS Forced Photometry Server (Shingles et al. AstroNote #2021-7).\n\nMore specifically:\nAT2025adgp was first detected on MJD 60991.136 (~0.5 days pre-GW) in the c-band with magnitude, m_c = 19.22 +/- 0.25 (AB) mag.\nAT2025adgq was first detected on MJD 60988.111 (~3.5 days pre-GW) in the o-band with magnitude, m_o = 19.03 +/- 0.18 (AB) mag.\n\nGiven these pre-detections, we expect that both AT2025adgp and AT2025adgq are young, rising supernovae, unrelated to the GW signal, S251112cm. However, the exact nature of the optical counterpart to a sub-solar-mass compact object merger event is uncertain, and so we cannot rule out that these transient phenomena are related in some way. Further monitoring of these candidate events will occur with ATLAS.\n\nThe Asteroid Terrestrial-impact Last Alert System (ATLAS) project is primarily funded to search for Near-Earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, University of Oxford, the Queen's University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile.",
"published": "2025-11-13T12:12:31.452667Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-13T12:12:31.452694Z",
"modified": "2025-11-13T12:12:31.477891Z",
"targets": []
},
{
"id": 5795535,
"topic": "gcn.circulars",
"uuid": "d9b43feb-d5fb-4067-80b9-3b85c459f481",
"title": "LIGO/Virgo/KAGRA S251112cm: Detection of two young transients by BlackGEM/MeerLICHT: AT2025adgp and AT2025adgq",
"submitter": "Paul Groot at Radboud University Nijmegen <p.groot@astro.ru.nl>",
"authors": "Paul Groot at Radboud University Nijmegen <p.groot@astro.ru.nl>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42663"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Detection of two young transients by BlackGEM/MeerLICHT: AT2025adgp and AT2025adgq",
"createdOn": 1763023570662,
"submitter": "Paul Groot at Radboud University Nijmegen <p.groot@astro.ru.nl>",
"circularId": 42663,
"submittedHow": "web"
},
"message_text": "P.J. Groot (Radboud/UCT/SAAO) , H. Tranin (Barcelona), J. van Roestel (ISTA), P.M. Vreeswijk (Radboud), D. Pieterse (Radboud), G. Leloudas (DTU Space), N. Blagorodnova (Barcelona), S. Bloemen (Radboud), G. Ramsay (Armagh), S. Scaringi (Durham) report on behalf of the BlackGEM and MeerLICHT consortia: \n\n\"The BlackGEM and MeerLICHT telescopes (Groot et al., 2024) reacted to the LVK-announced gravitational wave event S251112cm (LVK2025, GCN Circ. 42650). Both telescope systems covered about 50% of the 90% error box, primarily the part located in the Southern Hemisphere. A detailed overview of observations will be given in a subsequent report. Here we report the detection of AT2025adgp (BGEM J014746.20-514925.5), and AT2025adgq (MLT J002931.8-393051.6) as two newly detected transients in the BlackGEM/MeerLICHT footprint, which, on average, had a limiting magnitude for new transients of q~19.8. \n\nAT2025adgp is located at RA, Dec (ICRS) = 01:47:46.202 -51:49:25.52 (26.942508d, -51.823756d) with an uncertainty of 0.1\" in each coordinate. It was detected on 2025-11-13 03:09:48 and 03:25:29 UT in the BlackGEM q-band (440-720 nm) filter using the BG-2 telescope, at, respectively, q=19.31+/-0.12 and q=19.29+/-0.12. The first detection was 11h50m after the LVK Trigger time. The transient is located in the southern outskirts of a face-on spiral galaxy WISExSCOS J014746.23-514922.5, listed in the Regalade catalog (Tranin et al., 2025) at a luminosity distance of D_L =246 Mpc with a large standard deviation, and in the GLADE+ (Dalya et al., 2020) catalog at D_L = 250 +/- 45 Mpc. If the galaxy is the host of AT2025adgp this would put its distance at the upper edge of consistency with the distance to S251112cm as announced by the LVK collaboration at D_S251112cm = 96 +/- 29 Mpc. \n\nAT2025adgq is located at RA,Dec (ICRS) = 00:29:31.8, -39:30:51.6 (7.38245842d, -39.5143190d) with an uncertainty of 0.1” in each coordinate. It was detected on 2025-11-13 00:03:38 and 00:04:43 UT in the BlackGEM q-band (440-720 nm) filter using the MeerLICHT telescope at, q=19.28+/-0.10 in each exposure. The first detection was 08h44m after the LVK trigger. The BlackGEM array also detected AT2025adgq on 2025-11-13 01:05:23 UT and 01:22:00 UT using the BG-2 telescope at q=19.28 +/- 0.10 and q=19.41 +/- 0.1, respectively. The transient is located in the north-eastern elongation of an oblated galaxy, WISExSCOS J002932.49-393059.7, listed in the Regalade catalog at a luminosity distance of D_L = 279 +/- 130 Mpc, and in the GLADE+ catalog at D_L = 300 +/- 68 Mpc. If the galaxy is the host of AT2025adqp this would put its distance at the upper edge of consistency with the distance to S251112cm as announced by the LVK collaboration. \n\nWe encourage spectroscopic classification of AT2025adgp and AT2025adgq to confirm their nature and distance, and therefore the possibility of them being a counterpart to S251112cm.\"\n\nReferences: \nGroot et al., 2024, PASP 136, 5003, Tranin et al., 2025, arXiv250813267T, Dalya et al., 2020, VizieR On-line Data Catalog: VII/275; LVK2025, 2025, GCN 42650\n\n",
"published": "2025-11-13T09:27:34.966904Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-13T09:27:34.966931Z",
"modified": "2025-11-13T09:27:34.974219Z",
"targets": []
},
{
"id": 5795408,
"topic": "gcn.circulars",
"uuid": "638f491a-abbe-448c-9467-9929aca60894",
"title": "LIGO/Virgo/KAGRA S251112cm: Initial GOTO-South observations",
"submitter": "kendall.ackley@warwick.ac.uk",
"authors": "kendall.ackley@warwick.ac.uk",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42658"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Initial GOTO-South observations",
"version": 2,
"editedBy": "Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of kendall.ackley@warwick.ac.uk",
"editedOn": 1763001737175,
"createdOn": 1762987643407,
"submitter": "kendall.ackley@warwick.ac.uk",
"circularId": 42658,
"submittedHow": "web"
},
"message_text": "K. Ackley, B. Godson, D. O'Neill, B. P. Gompertz, M. Dyer, J. Lyman, K. Ulaczyk, S. Belkin, T. Killestein, A. Kumar, M. Pursiainen, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, J. Casares Velásquez, L. K. Nuttall, report on behalf of the GOTO collaboration:\n\nWe carried out optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al 2024) in response to the LIGO/Virgo/KAGRA gravitational wave candidate event S251112cm (GCN 42650).\n\nTargeted observations were performed by GOTO-South (Siding Spring, Australia) starting at 2025-11-12 16:09:51 UT, (+0.85h post trigger) and continued through to 2025-11-12 17:51:21 UT (+2.54h post trigger). A total of 39 image sets with exposures of 4x60s and 4x90s were taken across 6 unique pointings, covering 250.5 sq. degrees within the 90% localisation contour of the initial skymap. We covered approximately 14.6% of the total 2D localisation probability with an average 5-sigma depth of L~19.9 mag (AB). \n\nImages were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks.\n\nWithin the initial skymap, we identify 2 optical sources within the 90% contour and 1 optical source within the 99% probability contour. We find no convincing evidence of excess flux in either GOTO25jyg/AT2025addc or GOTO25jya/AT2025adcv prior to the GW trigger time in previous GOTO observations or the ZTF observations provided by the Lasair broker (Smith et al. 2019). The ATLAS forced photometry server (Shingles et al. 2021) returns recent detections for GOTO25jyg and GOTO25jya, albeit at low significance. We encourage further analysis to confirm these pre-detections.\n\nWe note that GOTO25jya appears to be associated with a GLADE+ galaxy HyperLEDA 422311 with zphot ~ 0.01 (D_L~474 Mpc) which, if correct, would put it outside the nominal luminosity distance estimates of S251112cm. \n\nWe do not find a host galaxy underlying GOTO25jyg. There is a galaxy located 9.27 arcsec from the candidate’s position within the Legacy DR10 photometric redshift catalog with zphot ~ 0.3 (Dey et al. 2019). \n\nGOTO25jye/AT2025adcy is located outside of the 90% probability contour of the initial skymap and is potentially associated with a GLADE+ galaxy HyperLEDA 389528 at zphot ~ 0.13 (D_L~664 Mpc). This association would make this candidate unlikely to be related to S251112cm.\n\n\n| Internal name | IAU name | RA(J2000) | Dec(J2000) | Mag(AB) |\n| ------------- | ---------- | ----------- | ------------ |--------------- |\n| GOTO25jyg | AT2025addc | 04:55:26.13 | -53:09:43.61 | 19.93 +/- 0.20 |\n| GOTO25jya | AT2025adcv | 03:05:58.60 | -54:09:06.60 | 19.30 +/- 0.10 |\n| GOTO25jye | AT2025adcy | 04:35:28.56 | -57:28:31.64 | 19.71 +/- 0.12 |\n\t\n\nMagnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and not corrected for Galactic extinction. Continued observations are planned from both GOTO sites, weather permitting.\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, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC).\n",
"published": "2025-11-13T02:42:18.530563Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-13T02:42:18.530584Z",
"modified": "2025-11-13T02:42:18.540886Z",
"targets": []
},
{
"id": 5795398,
"topic": "gcn.circulars",
"uuid": "0ddf9c32-3f40-4ea0-bee8-5002e75fef94",
"title": "LIGO/Virgo/KAGRA S251112cm: Coverage and upper limits from MAXI/GSC observations",
"submitter": "Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>",
"authors": "Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42659"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Coverage and upper limits from MAXI/GSC observations",
"createdOn": 1763000967453,
"submitter": "Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>",
"circularId": 42659,
"submittedHow": "web"
},
"message_text": "H. Hiramatsu, S. Sugita, M. Serino, Y. Kawakubo, Y. Kondo (AGU)\nH. Negoro, M. Nakajima, K. Takagi (Nihon U.),\nN. Kawai, T. Mihara, (RIKEN),\n\nreport on behalf of the MAXI team:\n\nWe examined MAXI/GSC all-sky X-ray images (2-20 keV)\nafter compact binary merger candidate S251112cm at 2025-11-12 15:18:45.362 UTC (GCN #42650).\n\nAt the trigger time of S251112cm, the high-voltage of MAXI/GSC was on.\nThe instantaneous field of view of GSC at the GW trigger time covered 1% of the 90% credible region\nof the bayestar sky map, in which we found no significant new X-ray source.\nThe first one-orbit (92 min) scan observation with GSC after the event covered 72%\nof the 90% credible region of the bayestar skymap from 15:18:45 to 16:50:09 UTC (T0+0 to T0+5484 sec).\n\nNo significant new source was found in the region in the one-orbit scan observation.\nA typical 1-sigma averaged upper limit obtained in one scan observation\nis 20 mCrab at 2-20 keV.\n\nIf you require information about X-ray flux by MAXI/GSC at specific coordinates,\nplease contact the submitter of this circular by email.",
"published": "2025-11-13T02:29:33.382733Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-13T02:29:33.382752Z",
"modified": "2025-11-13T02:29:33.392384Z",
"targets": []
},
{
"id": 5795315,
"topic": "gcn.circulars",
"uuid": "e1596663-e69d-4ac9-8386-6500de543b3e",
"title": "LIGO/Virgo/KAGRA S251112cm: Initial GOTO-South observations",
"submitter": "kendall.ackley@warwick.ac.uk",
"authors": "kendall.ackley@warwick.ac.uk",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42658"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Initial GOTO-South observations",
"createdOn": 1762987643407,
"submitter": "kendall.ackley@warwick.ac.uk",
"circularId": 42658,
"submittedHow": "web"
},
"message_text": "K. Ackley, B. Godson, D. O'Neill, B. P. Gompertz, M. Dyer, J. Lyman, K. Ulaczyk, S. Belkin, T. Killestein, A. Kumar, M. Pursiainen, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, J. Casares Velásquez, L. K. Nuttall, report on behalf of the GOTO collaboration:\n\nWe carried out optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al 2024) in response to the LIGO/Virgo/KAGRA gravitational wave candidate event S251112cm (GCN 42650).\n\nTargeted observations were performed by GOTO-South (Siding Spring, Australia) starting at 2025-11-12 16:09:51 UT, (+0.85h post trigger) and continued through to 2025-11-12 17:51:21 UT (+2.54h post trigger). A total of 39 image sets with exposures of 4x60s and 4x90s were taken across 6 unique pointings, covering 250.5 sq. degrees within the 90% localisation contour of the initial skymap. We covered approximately 14.6% of the total 2D localisation probability with an average 5-sigma depth of L~19.9 mag (AB). \n\nImages were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks.\n\nWithin the initial skymap, we identify 2 optical sources within the 90% contour and 1 optical source within the 99% probability contour. We find no convincing evidence of excess flux in either GOTO25jyg/AT2025addc or GOTO25jya/AT2025adcv prior to the GW trigger time in previous GOTO observations or the ZTF observations provided by the Lasair broker (Smith et al. 2019). The ATLAS forced photometry server (Shingles et al. 2021) returns recent detections for GOTO25jyg and GOTO25jya, albeit at low significance. We encourage further analysis to confirm these pre-detections.\n\nWe note that GOTO25jya appears to be associated with a GLADE+ galaxy HyperLEDA 422311 with zphot~0.01 (D_L~474 Mpc) which, if correct, would put it outside the nominal luminosity distance estimates of S251112cm. \n\nWe do not find a host galaxy underlying GOTO25jyg. There is a galaxy located 9.27 arcsec from the candidate’s position within the Legacy DR10 photometric redshift catalog with zphot ~ 0.3 (Dey et al. 2019). \n\nGOTO25jye/AT2025adcy is located outside of the 90% probability contour of the initial skymap and is potentially associated with a GLADE+ galaxy HyperLEDA 389528 at zphot ~ 0.13 (D_L~664 Mpc). This association would make this candidate unlikely to be related to S251112cm.\n\n\n| Internal name | IAU name | RA(J2000) | Dec(J2000) | Mag(AB) |\n| ------------- | ---------- | ----------- | ------------ |--------------- |\n| GOTO25jyg | AT2025addc | 04:55:26.13 | -53:09:43.61 | 19.93 +/- 0.20 |\n| GOTO25jya | AT2025adcv | 03:05:58.60 | -54:09:06.60 | 19.30 +/- 0.10 |\n| GOTO25jye | AT2025adcy | 04:35:28.56 | -57:28:31.64 | 19.71 +/- 0.12 |\n\t\n\nMagnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and not corrected for Galactic extinction. Continued observations are planned from both GOTO sites, weather permitting.\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, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC).\n",
"published": "2025-11-13T00:34:31.788450Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-13T00:34:31.788473Z",
"modified": "2025-11-13T00:34:31.803368Z",
"targets": []
},
{
"id": 5795242,
"topic": "gcn.circulars",
"uuid": "bc5463bf-712f-4609-b8f0-e42f58812933",
"title": "LIGO/Virgo/KAGRA S251112cm: Upper limits from Fermi-GBM Observations",
"submitter": "Angus Jameson <abj0023@uah.edu>",
"authors": "Angus Jameson <abj0023@uah.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42655"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Upper limits from Fermi-GBM Observations",
"createdOn": 1762983477642,
"submitter": "Angus Jameson <abj0023@uah.edu>",
"circularId": 42655,
"submittedHow": "web"
},
"message_text": "S. Bala (USRA) & A. Jameson (UAH) reports on behalf of the Fermi-GBM Team:\n\nFor S251112cm (GCN 42650) and using the initial/updated bayestar/Bilby skymap, Fermi-GBM was observing 68.6% of the localization probability at event time.\n\nThere was a Fermi-GBM onboard trigger 784653403/251112637, around two mins before the event time of the LIGO/Virgo/KAGRA (LVK) detection of GW S251112cm, due to local particles (GCN 42652). An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM also identified no counterpart candidates. The GBM targeted search, the most sensitive, coherent search for GRB-like signals, was run from +/-30 s around merger time, and also identified no counterpart candidates.\n\nPart of the LVK localization region is behind the Earth for Fermi, located at an RA=4.4, Dec=25.2 with a radius of 68 degrees. We therefore set upper limits on impulsive gamma-ray emission for the GW localization region visible to Fermi at merger time. Using the representative soft, normal, and hard GRB-like templates described in arXiv:1612.02395, we set the following 3 sigma flux upper limits over 10-1000 keV, weighted by GW localization probability (in units of 10^-7 erg/s/cm^2):\n\nTimescale Soft Normal Hard (Please put these in the appropriate units for 10^-7 erg/s/cm^2)\n------------------------------------\n0.128 s: 4.1 6.1 7.7\n1.024 s: 2.0 2.7 3.4\n8.192 s: 1.0 1.4 1.3\n\nAssuming the median luminosity distance of 96 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^47 erg/s):\n\nTimescale Soft Normal Hard\n------------------------------------\n0.128s: 6.9 9.6 19.8\n1.024s: 3.3 4.2 8.7\n8.192s: 1.7 2.2 3.3",
"published": "2025-11-12T21:38:06.166906Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-12T21:38:06.166929Z",
"modified": "2025-11-12T21:38:06.183797Z",
"targets": []
},
{
"id": 5795161,
"topic": "gcn.circulars",
"uuid": "2e159b5f-6f01-429a-8d4c-5e818cd32a30",
"title": "LIGO/Virgo/KAGRA S251112cm: NED Galaxies in the 3-Initial Localization Volume",
"submitter": "David Cook at Caltech/IPAC-NED <dcook@ipac.caltech.edu>",
"authors": "David Cook at Caltech/IPAC-NED <dcook@ipac.caltech.edu>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42653"
},
"format": "text/markdown",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: NED Galaxies in the 3-Initial Localization Volume",
"createdOn": 1762966807827,
"submitter": "David Cook at Caltech/IPAC-NED <dcook@ipac.caltech.edu>",
"circularId": 42653,
"submittedHow": "web"
},
"message_text": "David O. Cook (Caltech/IPAC), Rick Ebert (Caltech/IPAC), George Helou (Caltech/IPAC), Joseph M. Mazzarella (Caltech/IPAC), Marion Schmitz (Caltech/IPAC), and Leo Singer (NASA/GSFC)\n\nOn behalf of the NASA/IPAC Extragalactic Database (NED) Team.\n\nWe spatially cross-matched the LVK S251112cm-3-Initial sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023; https://ned.ipac.caltech.edu/NED::LVS/) which is a subset of NED with a redshift or redshift-independent distance less than 1000 Mpc. We find 7731 galaxies within the 90% containment volume, and we list here the top 20 galaxies sorted by the joint probability of the 3D localization and the WISE W1 luminosity (an observable proxy for stellar mass). For the full or top 20 list of galaxies in the 90% volume go either to the NED Gravitational Wave Followup service at https://ned.ipac.caltech.edu/uri/NED::GWF/ or click on the following links:\n\nFull List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S251112cm/3 \nTop 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S251112cm/3/20\n\nThe NED-GWF service provides downloadable galaxy lists and visualizations for candidate host galaxies. For each GW alert, these products are automatically generated and made available within minutes to expedite efficient electromagnetic follow-up observations. The NED top 20 list is sorted by the joint probability of the 3D localization and the WISE W1 luminosity, but users can sort on additional pre-computed prioritization metrics (star formation rate, P_3D * P_SFR; and specific star formation rate, P_3D * P_sSFR; etc.) which are available via downloading the entire galaxy list inside the event's probability volume.\n\n| objname| ra| dec|objtype| DistMpc|DistMpc_unc| m_NUV| m_NUV_unc| m_Ks| m_Ks_unc| m_W1| m_W1_unc| P_3D|P_3D_LumW1|\n|-------------------------|--------------|--------------|-------|-----------|-----------|------------|------------|------------|------------|------------|------------|--------|----------|\n| NGC 2960| 145.15161| 3.57703| G| 76.97| 7.94| 17.522| 0.003| 9.783| 0.038| 9.672| 0.002|1.71e-05| 1.08e-08|\n| IC 1471| 347.18676| -12.63948| G| 83.00| 17.58| 17.246| 0.027| 10.334| 0.035| 10.290| 0.006|1.79e-05| 7.44e-09|\n| NGC 7396| 343.09426| 1.09241| G| 81.16| 8.50| 17.854| 0.004| 8.699| 0.022| 8.557| 0.012|3.66e-06| 7.25e-09|\n| UGC 05226| 146.51479| 4.40348| G| 66.86| 15.78| 18.763| 0.092| 10.211| 0.041| 10.083| 0.089|2.17e-05| 7.08e-09|\n| IC 0564| 146.58792| 3.07130| G| 75.75| 2.62| null| null| 10.033| 0.035| 10.010| 0.006|1.51e-05| 6.79e-09|\n| NGC 3070| 149.52893| 10.35980| G| 60.25| 5.89| 18.225| 0.068| 9.260| 0.030| 9.503| 0.006|1.45e-05| 6.56e-09|\n| IC 1464B| 345.79587| -8.98909| G| 105.88| 0.59| null| null| 10.015| 0.036| 9.741| 0.006|5.69e-06| 6.38e-09|\n|WISEA J100012.04+093856.0| 150.05020| 9.64890| G| 78.82| 0.30| null| null| 11.073| 0.096| 10.233| 0.006|1.53e-05| 6.05e-09|\n| UGCA 150| 137.70611| -8.89069| G| 28.38| 0.82| null| null| 7.704| 0.006| 7.044| 0.041|5.28e-06| 5.11e-09|\n| IC 1633| 17.48145| -45.93116| G| 96.06| 3.43| null| null| 8.396| 0.025| 8.999| 0.006|2.80e-06| 5.10e-09|\n| NGC 3540| 167.31704| 36.02108| G| 93.24| 0.04| 19.626| 0.150| 10.168| 0.041| 10.319| 0.006|9.87e-06| 5.03e-09|\n| NGC 2987| 146.42281| 4.94189| G| 54.46| 0.58| 17.338| 0.002| 10.146| 0.048| 9.912| 0.006|1.97e-05| 4.99e-09|\n| NGC 7646| 351.02906| -11.86050| G| 79.59| 2.73| 16.328| 0.004| 10.358| 0.037| 8.371| 0.005|2.21e-06| 4.94e-09|\n| MCG -01-24-010| 140.09147| -7.88074| G| 53.94| 2.54| 15.885| 0.007| 10.054| 0.032| 9.821| 0.030|1.78e-05| 4.81e-09|\n| ESO 197- G 021| 31.13585| -52.17213| G| 87.54| 0.39| null| null| 9.099| 0.026| 9.375| 0.006|4.26e-06| 4.56e-09|\n| NGC 4187| 183.37201| 50.74150| G| 120.62| 5.52| 18.691| 0.027| 9.772| 0.027| 9.930| 0.006|3.73e-06| 4.56e-09|\n| UGC 05267| 147.47044| 9.09562| G| 80.08| 3.03| null| null| 10.147| 0.042| 10.208| 0.006|1.08e-05| 4.52e-09|\n| NGC 7364| 341.10153| -0.16213| G| 76.48| 8.25| 16.366| 0.001| 9.478| 0.028| 9.218| 0.003|4.69e-06| 4.46e-09|\n| NGC 0010| 2.14394| -33.85835| G| 87.84| 3.70| null| null| 9.205| 0.042| 9.975| 0.006|7.18e-06| 4.45e-09|\n| UGC 05855| 161.15400| 26.18153| G| 91.46| 2.06| 17.681| 0.037| 10.212| 0.028| 10.184| 0.006|7.99e-06| 4.45e-09|\n\nTable 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S251112cm sorted by the joint probability of 3D position and WISE W1 luminosity (P_3D * P_LumW1). Galaxy is the NED preferred name. RA and Dec are the Equatorial coordinates in degrees (J2000). Objtype is the object type of the galaxy candidate. Distance is the distance to the galaxy in Mpc. m_NUV and mErr_NUV are the apparent magnitude and error from GALEX. m_Ks and mErr_Ks are the apparent magnitude and error from 2MASS. m_W1 and mErr_W1 are the apparent magnitude and error from AllWISE. P_3D is the probability that the galaxy is in the volume given the distance of GW event. P_3D_LumW1 is the joint probability within the volume weighted by the WISE1 luminosity of the galaxy (P_3D * P_LumW1). \n",
"published": "2025-11-12T17:00:16.366421Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-12T17:00:16.366446Z",
"modified": "2025-11-12T17:00:16.524690Z",
"targets": []
},
{
"id": 5795141,
"topic": "gcn.circulars",
"uuid": "6c356343-34d3-4f1d-aed5-ac3229283552",
"title": "LIGO/Virgo/KAGRA S251112cm: Identification of a GW compact binary merger candidate",
"submitter": "Alicia Calafat <alicia.calafat@ligo.org>",
"authors": "Alicia Calafat <alicia.calafat@ligo.org>",
"data": {
"urls": {
"gcn_circular": "https://gcn.nasa.gov/circulars/42650"
},
"format": "text/plain",
"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S251112cm",
"subject": "LIGO/Virgo/KAGRA S251112cm: Identification of a GW compact binary merger candidate",
"createdOn": 1762962925787,
"submitter": "Alicia Calafat <alicia.calafat@ligo.org>",
"circularId": 42650,
"submittedHow": "web"
},
"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe identified the compact binary merger candidate S251112cm during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-11-12 15:18:45.362 UTC (GPS time: 1446995943.362). The candidate was found by the MBTA SSM [1] analysis pipeline.\n\nS251112cm is an event of interest because its false alarm rate, as estimated by the online analysis, is 5.1e-09 Hz, or about one in 6 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S251112cm\n\nThe analysis which found this candidate used a template bank including sub-solar-mass components. The usual classification probabilities for BNS, NSBH, or BBH binaries versus Terrestrial noise are not calculated for this candidate. The probability of matter remaining outside the final compact object (HasRemnant) [2] is not estimated either.\n\nAssuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass between 1 and 3 solar masses (HasNS) is 8%. [2] The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. The probability that the lighter compact object is below 1 solar mass (HasSSM) is >99%.\n\nThe source chirp mass falls with highest probability in the bin (0.1, 0.87) solar masses, assuming the candidate is astrophysical in origin.\n\nTwo sky maps are available at this time and can be retrieved from the GraceDB event page:\n * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices about 57 seconds after the candidate event time.\n * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time.\n\nThe preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 1220 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 96 +/- 29 Mpc (a posteriori mean +/- standard deviation).\n\nFor further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.\n\n [1] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234\n [2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [3] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013",
"published": "2025-11-12T15:55:34.943118Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-11-12T15:55:34.943141Z",
"modified": "2025-11-12T15:55:34.965131Z",
"targets": []
}
]
}
]
}
