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{
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"uuid": "834633ee-dd4d-4153-b146-a2b6bcb9fede",
"title": "LIGO/Virgo/KAGRA S250818t: Updated Sky localization",
"submitter": "lucy.thomas@ligo.org",
"authors": "lucy.thomas@ligo.org",
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"subject": "LIGO/Virgo/KAGRA S250818t: 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 S250818t (GCN Circular 41404). 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/S250818t\n\nFor the Bilby.multiorder.fits,0 sky map, the 90% credible region is 319 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1209 +/- 290 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": "2025-09-08T08:08:49.302548Z",
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{
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"title": "LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate",
"submitter": "Jiyoon Sun <jiyoon.sun.h@gmail.com>",
"authors": "Jiyoon Sun <jiyoon.sun.h@gmail.com>",
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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 S250818t during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-08-18 02:08:58.392 UTC (GPS time: 1439518156.392). The candidate was found by the GstLAL [1], MBTA [2], and PyCBC Live [3] analysis pipelines.\n\nS250818t is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.7e-11 Hz, or about one in 1e3 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S250818t\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%. [4] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [4] 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 [5], distributed via GCN and SCiMMA notices about 32 seconds after the candidate event time.\n * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [5], 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 377 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1311 +/- 350 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] 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 [2] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234\n [3] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a\n [4] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [5] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013",
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{
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"uuid": "ec20ce67-115a-47ef-b63b-edaf7b225f24",
"title": "LIGO/Virgo/KAGRA S250901cb: Updated Sky localization",
"submitter": "Michael J. Williams at University of Portsmouth <michael.williams@ligo.org>",
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"bibcode": "2025GCN.41656....1L",
"eventId": "LIGO/Virgo/KAGRA S250901cb",
"subject": "LIGO/Virgo/KAGRA S250901cb: 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 S250901cb (GCN Circular 41638). 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/S250901cb\n\nFor the Bilby.multiorder.fits,0 sky map, the 90% credible region is 581 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2018 +/- 482 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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{
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"title": "LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate",
"submitter": "shoki.iwaguchi@ligo.org",
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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 S250901cb during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-09-01 18:59:41.965 UTC (GPS time: 1440788399.965). The candidate was found by the Aframe [1], cWB BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines.\n\nS250901cb is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-14 Hz, or about one in 1e6 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S250901cb\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 (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 [8], distributed via GCN and SCiMMA notices about 24 seconds after the candidate event time.\n * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [9], 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 well fit by an ellipse with an area of 935 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis):\n icrs; ellipse(13h05m, -07d35m, 30.96d, 9.71d, 118.56d)\nMarginalized over the whole sky, the a posteriori luminosity distance estimate is 1960 +/- 524 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] Chatterjee et al. MLST 5, 045030 (2024) doi:10.1088/2632-2153/ad8982\n [9] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013",
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"title": "LIGO/Virgo/KAGRA S250901cb: Updated Sky localization",
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{
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"title": "LIGO/Virgo/KAGRA S250901cb: 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 S250901cb during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-09-01 18:59:41.965 UTC (GPS time: 1440788399.965). The candidate was found by the Aframe [1], cWB BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines.\n\nS250901cb is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-14 Hz, or about one in 1e6 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S250901cb\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 (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 [8], distributed via GCN and SCiMMA notices about 24 seconds after the candidate event time.\n * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [9], 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 well fit by an ellipse with an area of 935 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis):\n icrs; ellipse(13h05m, -07d35m, 30.96d, 9.71d, 118.56d)\nMarginalized over the whole sky, the a posteriori luminosity distance estimate is 1960 +/- 524 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] Chatterjee et al. MLST 5, 045030 (2024) doi:10.1088/2632-2153/ad8982\n [9] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013",
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{
"id": 5781044,
"topic": "gcn.circulars",
"uuid": "b829ff07-49e7-4a56-affc-0c421cbd9d22",
"title": "LIGO/Virgo/KAGRA S250906ca: Updated Sky localization",
"submitter": "natalie.williams@uni-potsdam.de",
"authors": "natalie.williams@uni-potsdam.de",
"data": {
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"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"bibcode": "2025GCN.41780....1L",
"eventId": "LIGO/Virgo/KAGRA S250906ca",
"subject": "LIGO/Virgo/KAGRA S250906ca: Updated Sky localization",
"createdOn": 1757534160311,
"submitter": "natalie.williams@uni-potsdam.de",
"circularId": 41780,
"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 S250906ca (GCN Circular 41745). 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/S250906ca\n\nFor the Bilby.multiorder.fits,0 sky map, the 90% credible region is 516 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1121 +/- 266 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": "2025-09-22T08:08:50.474185Z",
"message_parser": "GCN Circular Parser v2",
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"created": "2025-09-22T08:08:50.474193Z",
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{
"id": 5781038,
"topic": "gcn.circulars",
"uuid": "3254846d-4550-4885-bb04-746ee951fdff",
"title": "LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate",
"submitter": "Mayara Hilgert Pacheco at LIGO <mayara.pacheco@inpe.br>",
"authors": "Mayara Hilgert Pacheco at LIGO <mayara.pacheco@inpe.br>",
"data": {
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"bibcode": "2025GCN.41745....1L",
"eventId": "LIGO/Virgo/KAGRA S250906ca",
"subject": "LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate",
"createdOn": 1757268104447,
"submitter": "Mayara Hilgert Pacheco at LIGO <mayara.pacheco@inpe.br>",
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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 S250906ca during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-09-06 12:23:59.099 UTC (GPS time: 1441196657.099). Automated LVK preliminary notices as well as this initial circular were delayed by a day due to the consequences of a power outage in our main computing center for processing low-latency alerts. The candidate was found by the GstLAL [1] and MBTA [2] analysis pipelines.\n\nS250906ca is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.1e-13 Hz, or about one in 1e5 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S250906ca\n\nThe classification of the GW signal, in order of descending probability, is BBH (>99%), NSBH (<1%), Terrestrial (<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%. [3] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [3] 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 6%.\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 [4], distributed via GCN and SCiMMA notices about a day after the candidate event time.\n * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [4], distributed via GCN and SCiMMA notices about a day 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 520 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1195 +/- 307 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] 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 [2] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234\n [3] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [4] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013\n",
"published": "2025-09-22T08:08:50.411952Z",
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"retracted": false,
"created": "2025-09-22T08:08:50.411960Z",
"modified": "2025-09-22T08:08:50.415267Z",
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},
{
"id": 5777621,
"topic": "gcn.circulars",
"uuid": "27722f4f-5444-4d96-aa2b-94ac966359d9",
"title": "LIGO/Virgo/KAGRA S250906ca: Updated Sky localization",
"submitter": "natalie.williams@uni-potsdam.de",
"authors": "natalie.williams@uni-potsdam.de",
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"$schema": "https://gcn.nasa.gov/schema/v4.5.0/gcn/circulars.schema.json",
"eventId": "LIGO/Virgo/KAGRA S250906ca",
"subject": "LIGO/Virgo/KAGRA S250906ca: Updated Sky localization",
"createdOn": 1757534160311,
"submitter": "natalie.williams@uni-potsdam.de",
"circularId": 41780,
"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 S250906ca (GCN Circular 41745). 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/S250906ca\n\nFor the Bilby.multiorder.fits,0 sky map, the 90% credible region is 516 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1121 +/- 266 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": "2025-09-10T19:56:09.449898Z",
"message_parser": "GCN Circular Parser v2",
"retracted": false,
"created": "2025-09-10T19:56:09.449918Z",
"modified": "2025-09-10T19:56:09.462417Z",
"targets": []
},
{
"id": 5776394,
"topic": "gcn.circulars",
"uuid": "53f66352-384a-4611-9802-b4366630ea77",
"title": "LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate",
"submitter": "Mayara Hilgert Pacheco at LIGO <mayara.pacheco@inpe.br>",
"authors": "Mayara Hilgert Pacheco at LIGO <mayara.pacheco@inpe.br>",
"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 S250906ca",
"subject": "LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate",
"createdOn": 1757268104447,
"submitter": "Mayara Hilgert Pacheco at LIGO <mayara.pacheco@inpe.br>",
"circularId": 41745,
"submittedHow": "web"
},
"message_text": "The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe identified the compact binary merger candidate S250906ca during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-09-06 12:23:59.099 UTC (GPS time: 1441196657.099). Automated LVK preliminary notices as well as this initial circular were delayed by a day due to the consequences of a power outage in our main computing center for processing low-latency alerts. The candidate was found by the GstLAL [1] and MBTA [2] analysis pipelines.\n\nS250906ca is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.1e-13 Hz, or about one in 1e5 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S250906ca\n\nThe classification of the GW signal, in order of descending probability, is BBH (>99%), NSBH (<1%), Terrestrial (<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%. [3] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [3] 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 6%.\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 [4], distributed via GCN and SCiMMA notices about a day after the candidate event time.\n * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [4], distributed via GCN and SCiMMA notices about a day 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 520 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1195 +/- 307 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] 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 [2] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234\n [3] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [4] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013\n",
"published": "2025-09-07T18:01:51.988635Z",
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"created": "2025-09-07T18:01:51.988656Z",
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"created": "2025-09-10T22:21:07.612430Z",
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"message": {
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"time_created": "2025-09-10T22:25:41Z",
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"created": "2025-09-10T22:25:42.899218Z",
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"id": 5777718,
"topic": "gcn.classic.text.ICECUBE_CASCADE",
"uuid": "31084690-4af3-47b9-86f2-12bb78f2b992",
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"title": "GCN/AMON NOTICE",
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"moon_postn": "32.17d {+02h 08m 40s} +17.03d {+17d 01' 59\"}",
"signalness": "9.0012e-01 [dn]",
"notice_date": "Thu 11 Sep 25 05:47:53 UT",
"notice_type": "ICECUBE Cascade",
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"discovery_date": "20929 TJD; 254 DOY; 25/09/11 (yy/mm/dd)",
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"message_text": "TITLE: GCN/AMON NOTICE\nNOTICE_DATE: Thu 11 Sep 25 05:47:53 UT\nNOTICE_TYPE: ICECUBE Cascade \nEVENT_NAME: IceCubeCascade-250911a\nSTREAM: 26\nRUN_NUM: 141344\nEVENT_NUM: 29341777\nSRC_RA: 111.9776d {+07h 27m 55s} (J2000),\n 112.3027d {+07h 29m 13s} (current),\n 111.3448d {+07h 25m 23s} (1950)\nSRC_DEC: -1.7676d {-01d 46' 02\"} (J2000),\n -1.8215d {-01d 49' 16\"} (current),\n -1.6648d {-01d 39' 52\"} (1950)\nSRC_ERROR: 13.28 [deg radius, stat+systematic, 90% containment]\nSRC_ERROR50: 7.28 [deg radius, stat+systematic, 50% containment]\nDISCOVERY_DATE: 20929 TJD; 254 DOY; 25/09/11 (yy/mm/dd)\nDISCOVERY_TIME: 16117 SOD {04:28:37.14} UT\nREVISION: 0\nENERGY: 96.63 [TeV]\nSIGNALNESS: 9.0012e-01 [dn]\nFAR: 0.3110 [yr^-1]\nSUN_POSTN: 169.66d {+11h 18m 39s} +4.45d {+04d 26' 52\"}\nSUN_DIST: 57.65 [deg] Sun_angle= 3.8 [hr] (West of Sun)\nMOON_POSTN: 32.17d {+02h 08m 40s} +17.03d {+17d 01' 59\"}\nMOON_DIST: 81.12 [deg]\nGAL_COORDS: 218.70, 7.29 [deg] galactic lon,lat of the event\nECL_COORDS: 114.05,-23.39 [deg] ecliptic lon,lat of the event\nSKYMAP_FITS_URL: https://roc.icecube.wisc.edu/public/hese_cascades/hese_60929_run00141344.evt000029341777.fits\nSKYMAP_PNG_URL: https://roc.icecube.wisc.edu/public/hese_cascades/hese_60929_run00141344.evt000029341777.png\nCOMMENTS: IceCube Cascade event. \nCOMMENTS: The position error is the combined statistical and the systematic. \n",
"published": "2025-09-11T05:47:53Z",
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"message_text": "\nThe LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:\n\nWe identified the compact binary merger candidate S250912f during real-time processing of data from LIGO Livingston Observatory (L1) and Virgo Observatory (V1) at 2025-09-12 06:40:08.840 UTC (GPS time: 1441694426.840). The candidate was found by the GstLAL [1] and SPIIR [2] analysis pipelines.\n\nS250912f is an event of interest because its false alarm rate, as estimated by the online analysis, is 2.9e-13 Hz, or about one in 1e5 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S250912f\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%. [3] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [3] 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 (44.0, 88.0) 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,1, an initial localization generated by BAYESTAR [4], distributed via GCN and SCiMMA notices about 27 seconds after the candidate event time.\n * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [4], 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,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 393 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2870 +/- 784 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] 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 [2] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023\n [3] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe\n [4] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013\n",
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"title": "LIGO/Virgo/KAGRA S250912f: Updated Sky localization",
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"authors": "natalie.williams@uni-potsdam.de",
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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 Livingston Observatory (L1) and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250912f (GCN Circular 41810). 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/S250912f\n\nFor the Bilby.multiorder.fits,0 sky map, the 90% credible region is 298 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2740 +/- 722 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 S250912f: 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 S250904cv during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-09-04 13:49:52.532 UTC (GPS time: 1441029010.532). 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\nS250904cv is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S250904cv\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 (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 * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 2 minutes after the candidate event time.\n * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 7 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 1237 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2414 +/- 670 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\n",
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"title": "LIGO/Virgo/KAGRA S250904ae: 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 S250904ae during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-09-04 03:33:07.667 UTC (GPS time: 1440992005.667). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], and PyCBC Live [6] analysis pipelines.\n\nS250904ae is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL:\n\nhttps://gracedb.ligo.org/superevents/S250904ae\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%. [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 (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 * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 24 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 1021 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3330 +/- 883 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",
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"title": "LIGO/Virgo/KAGRA S250912s: 2 counterpart neutrino candidate events from an IceCube neutrino search",
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"message_text": "IceCube Collaboration (http://icecube.wisc.edu/) reports:\n\nWe have performed a search for track-like muon neutrino candidate events detected by IceCube consistent with the sky localization of the low-significance gravitational-wave candidate event S250912s in a time range of 1000 seconds centered on the alert event time (2025-09-12 18:13:09 UTC to 2025-09-12 18:29:49 UTC) [1,2]. During this time period, IceCube was collecting good quality data. A single hypothesis test was conducted using 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 statistical significance estimation [3]. \n\nTwo track-like events were found in spatial and temporal coincidence with the gravitational-wave candidate S250912s calculated from the map circulated in the S250912s-2-Preliminary notice. This represents an overall p-value of 0.00927 for the Bayesian search. The p-value measures the consistency of the observed track-like events with the known atmospheric backgrounds for this single map (not accounting for statistical trials from multiple GW events). \n\nFurther details are available at https://gcn.nasa.gov/missions/icecube and 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(Bayesian)\n-------------------------------------------------------------------------------------\n-276.12 \t284.52 \t\t44.13 \t\t16.11 \t\t\t0.0115\n 19.10 \t275.72 \t\t24.65 \t\t 1.44 \t\t\t0.0530\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 individual p-value for the specific track event from this 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[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",
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