- vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 40442] GRB 251017A: Swift-BAT refined analysis
by GCN Circulars 19 Oct '25

19 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42366 SUBJECT: GRB 251017A: Swift-BAT refined analysis DATE: 25/10/19 01:53:31 GMT FROM: Rahul Gupta at NASA GSFC <rahul.gupta(a)nasa.gov> T. Parsotan (GSFC), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-60 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 251017A (trigger #1404904) (Gupta, et al., GCN Circ. 42322). The BAT ground-calculated position is RA, Dec = 335.404, 7.048 deg which is RA(J2000) = 22h 21m 37.0s Dec(J2000) = +07d 02' 54.4" with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 93%. The mask-weighted BAT light curve shows main emission followed by weaker emission. T90 (15-350 keV) is 116.90 +- 61.91 sec (estimated error including systematics). The time-averaged spectrum from T-5.48 to T+125.08 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.40 +- 0.20. The fluence in the 15-150 keV band is 1.2 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+6.41 sec in the 15-150 keV band is 1.3 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1404904 View this GCN Circular online at https://gcn.nasa.gov/circulars/42366. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40441] GRB 251016A: Fermi GBM Observation
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42365 SUBJECT: GRB 251016A: Fermi GBM Observation DATE: 25/10/18 23:23:26 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 14:59:19.76 UT on 16 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251016A (trigger 782319564/251016625), which is was detected by SVOM/ECLAIRs (Basa et al., GCN 42308), CALET-GBM (Kawakubo et al., GCN 42321), Glowbug (Woolf et al., GCN 42313) and Astro Sat CZTI (Arya et al., GCN 42327). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position. The angle from the Fermi LAT boresight is 42 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 0.32 s (50-300 keV). The time-averaged spectrum from T0-0.1 to T0+0.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.83 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 1317 +/- 145 keV. The event fluence (10-1000 keV) in this time interval is (3 +/- 0.08)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.13 s in the 10-1000 keV band is 34 +/- 2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/42365. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40440] GRB 251018A: Fermi GBM Observation
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42364 SUBJECT: GRB 251018A: Fermi GBM Observation DATE: 25/10/18 21:53:57 GMT FROM: Glowbug DEV <boyan.a.hristov(a)nasa.gov> B. Hristov (UAH) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 03:12:00.63 UT on 18 October 2025 , the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 251018A (trigger 782449925 / 251018133), which was also detected by the Swift/XRT (R. Gupta et al. 2025, GCN 42343) The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 42 degrees. The GBM light curve consists of multiple peaks, with a duration (T90) of about 27.1 s (50-300 keV). The time-averaged spectrum from T0-6.1 s to T0+21.5 s is well fit by a power law function with an exponential high-energy cutoff. The power law index is -0.91 +/- 0.09 and the cutoff energy, parameterized as Epeak, is 715 +/- 162 keV. The event fluence (10-1000 keV) in this time interval is (6.8 +/- 0.3)E-6 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3 s in the 10-1000 keV band 0.95 +/- 0.04 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/42364. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40439] GRB 251018A: BOOTES-5 and BOOTES-7 early optical detections
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42363 SUBJECT: GRB 251018A: BOOTES-5 and BOOTES-7 early optical detections DATE: 25/10/18 20:48:38 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> Y.-D. Hu (GXU), I. Perez-Garcia, A. J. Castro-Tirado, E. J. Fernandez-Garcia, M. D. Caballero-Garcia, S.-Y. Wu, R. Sanchez-Ramirez, and S. Guziy (IAA-CSIC), I. M. Carrasco (SMA), M. Gritsevich (Univ. of Helsinki), C. Perez del Pulgar (Univ. of Malaga), S. Jeong (ADD, Daejeon), G. Garcia-Segura and D. Hiriart (IA-UNAM, Ensenada), W. H. Lee (UNAM, Mexico DF), D.-R. Xiong (YNAO), B.-B. Zhang (NJU), and A. Maury (Space Obs., San Pedro de Atacama) on behalf of a larger collaboration, report: Following the detection of GRB251018A by Swift (Gupta et al., GCN 42343) and Fermi (Fermi GBM team, GCN 42342), the 0.6m BOOTES-5/JGU robotic telescope at San Pedro Martir Observatory (Mexico) automatically responded to this high-energy event starting on Oct 18, 03:12:45 UT (i.e., 43 sec after detection). Series of images in clear filter were gathered and we detect an optical source. Using USNO B-1.0 as a reference, we measure an initial magnitude of 16.78 +/- 0.16 in the first 1 x 5 s stacked image. Meanwhile, the 0.6m BOOTES-7 robotic telescope at Space Observatory (San Pedro de Atacama, Chile) also automatically observed the GRB location starting on Oct. 18, 03:13:22 UT (i.e. 80 s after trigger). The afterglow is also detected with 16.04 +/- 0.11. These detections are consistent with the one reported by MASTER (Lipunov et al., GCN 42346), TRT (Fu et al., GCN 42345), and UVOT (Kuin et al., GCN 42353). Further analysis of the additional images is ongoing. We would like to thank the staff at San Pedro Martir Observatory and San Pedro de Atacama Space Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/42363. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40438] GRB 251018A: Swift-XRT refined Analysis
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42362 SUBJECT: GRB 251018A: Swift-XRT refined Analysis DATE: 25/10/18 19:10:27 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> E. Ambrosi (INAF-IASFPA) , J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 7.5 ks of XRT data for GRB 251018A, from 63 s to 50.2 ks after the trigger. The data comprise 259 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=1.122 (+0.031, -0.029). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.68 (+0.15, -0.14). The best-fitting absorption column is 1.4 (+0.6, -0.5) x 10^21 cm^-2, consistent with the Galactic value of 9.4 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.81 (+0.25, -0.23) and a best-fitting absorption column of 2.1 (+1.1, -0.9) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (5.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.1 (+1.1, -0.9) x 10^21 cm^-2 Galactic foreground: 9.4 x 10^20 cm^-2 Excess significance: 2.0 sigma Photon index: 1.81 (+0.25, -0.23) If the light curve continues to decay with a power-law decay index of 1.122, the count rate at T+24 hours will be 6.4 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.6 x 10^-13 (3.3 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01405083. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42362. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40437] GRB 251018A: Enhanced Swift-XRT position
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42361 SUBJECT: GRB 251018A: Enhanced Swift-XRT position DATE: 25/10/18 18:58:38 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 2660 s of XRT Photon Counting mode data and 4 UVOT images for GRB 251018A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 282.04220, -37.02921 which is equivalent to: RA (J2000): 18h 48m 10.13s Dec (J2000): -37d 01' 45.2" with an uncertainty of 2.4 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at https://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42361. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40436] Fermi trigger No 782500909: Global MASTER-Net observations report
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42360 SUBJECT: Fermi trigger No 782500909: Global MASTER-Net observations report DATE: 25/10/18 18:01:02 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB251018.72 (trigger No 782500909,16h 23m 38.40s , -85d 57m 00.0s, R=3.1) errorbox 721 sec after notice time and 754 sec after trigger time at 2025-10-18 17:34:19 UT, with upper limit up to 16.1 mag. Observations started at twilight. The observations began at zenith distance = 56 deg. The sun altitude is -9.4 deg. The galactic latitude b = -25 deg., longitude l = 307 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3017672 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 785 | 2025-10-18 17:34:19 | MASTER-SAAO | (16h 29m 10.44s , -85d 56m 26.8s) | C | 60 | 15.2 | 864 | 2025-10-18 17:35:38 | MASTER-SAAO | (16h 29m 10.67s , -85d 56m 25.2s) | C | 60 | 16.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42360. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40435] GRB 251016A: HXMT/HE detection
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42359 SUBJECT: GRB 251016A: HXMT/HE detection DATE: 25/10/18 16:40:50 GMT FROM: xueyuan zao <zaoxueyuan(a)gmail.com> Xue-Yuan Zao, Chen-Wei Wang, Zheng-Hang Yu, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-10-16T14:59:19.750 (T0), Insight-HXMT/HE detected the short burst GRB 251016A, which is also detected by SVOM/ECLAIRs (Basa et al., GCN 42308), FERMI-GBM (Fermi GBM team, GCN 42309), CALET-GBM (Kawakubo et al., GCN 42321), Glowbug (Woolf et al., GCN 42313) and Astro Sat CZTI (Arya et al., GCN 42327). The Insight-HXMT/HE light curve mainly consists of a single pulse with a T90 of 0.34 +/-0.06 s. The total counts from this burst is 2297 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251016A.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 30-1000 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/42359. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40434] IceCube Alert 251018.21: Global MASTER-Net observations report
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42358 SUBJECT: IceCube Alert 251018.21: Global MASTER-Net observations report DATE: 25/10/18 16:39:32 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the IceCube Alert 251018.21 (trigger No 22018019,21h 25m 13.92s , +39d 11m 09.6s, R=2.69) errorbox 39638 sec after notice time and 39688 sec after trigger time at 2025-10-18 16:07:11 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 8 deg. The sun altitude is -19.7 deg. The galactic latitude b = -8 deg., longitude l = 86 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3017315 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 22029 | 2025-10-18 11:12:21 | MASTER- | (21h 25m 26.91s , +38d 32m 19.1s) | C | 60 | 18.7 | Coadd 22142 | 2025-10-18 11:14:15 | MASTER- | (21h 34m 49.32s , +38d 32m 13.7s) | C | 60 | 18.4 | Coadd 22136 | 2025-10-18 11:14:33 | MASTER- | (21h 24m 42.35s , +40d 38m 41.0s) | C | 10 | 18.2 | 22149 | 2025-10-18 11:14:47 | MASTER- | (21h 24m 42.32s , +40d 38m 40.6s) | C | 10 | 18.3 | 22163 | 2025-10-18 11:15:00 | MASTER- | (21h 24m 42.33s , +40d 38m 40.8s) | C | 10 | 18.3 | 22176 | 2025-10-18 11:15:13 | MASTER- | (21h 24m 42.36s , +40d 38m 40.0s) | C | 10 | 18.3 | 22189 | 2025-10-18 11:15:27 | MASTER- | (21h 24m 42.37s , +40d 38m 39.1s) | C | 10 | 18.3 | 22203 | 2025-10-18 11:15:40 | MASTER- | (21h 24m 42.39s , +40d 38m 39.0s) | C | 10 | 18.3 | 22216 | 2025-10-18 11:15:54 | MASTER- | (21h 24m 42.42s , +40d 38m 38.2s) | C | 10 | 18.3 | 22230 | 2025-10-18 11:16:07 | MASTER- | (21h 24m 42.40s , +40d 38m 37.6s) | C | 10 | 18.2 | 22244 | 2025-10-18 11:16:21 | MASTER- | (21h 24m 42.40s , +40d 38m 37.0s) | C | 10 | 18.2 | 22266 | 2025-10-18 11:16:43 | MASTER- | (21h 24m 42.40s , +40d 38m 36.1s) | C | 10 | 18.4 | 22280 | 2025-10-18 11:16:58 | MASTER- | (21h 24m 42.41s , +40d 38m 35.3s) | C | 10 | 18.4 | 22294 | 2025-10-18 11:17:11 | MASTER- | (21h 24m 42.40s , +40d 38m 34.7s) | C | 10 | 18.4 | 22307 | 2025-10-18 11:17:25 | MASTER- | (21h 24m 42.46s , +40d 38m 34.3s) | C | 10 | 18.3 | 22324 | 2025-10-18 11:17:38 | MASTER- | (21h 24m 42.44s , +40d 38m 34.3s) | C | 15 | 18.7 | 22342 | 2025-10-18 11:17:57 | MASTER- | (21h 24m 42.43s , +40d 38m 32.8s) | C | 15 | 18.7 | 22361 | 2025-10-18 11:18:16 | MASTER- | (21h 24m 42.47s , +40d 38m 32.7s) | C | 15 | 18.7 | 22380 | 2025-10-18 11:18:34 | MASTER- | (21h 24m 42.47s , +40d 38m 31.2s) | C | 15 | 18.7 | 22398 | 2025-10-18 11:18:52 | MASTER- | (21h 24m 42.73s , +40d 38m 28.8s) | C | 15 | 17.7 | 22417 | 2025-10-18 11:19:11 | MASTER- | (21h 24m 42.65s , +40d 38m 27.9s) | C | 15 | 17.4 | 22987 | 2025-10-18 11:28:20 | MASTER- | (21h 31m 15.12s , +40d 24m 56.9s) | C | 60 | 19.3 | Coadd 23065 | 2025-10-18 11:29:38 | MASTER- | (21h 20m 28.77s , +36d 38m 22.6s) | C | 60 | 19.3 | Coadd 23238 | 2025-10-18 11:32:30 | MASTER- | (21h 24m 47.36s , +40d 38m 33.7s) | C | 60 | 19.4 | Coadd 23395 | 2025-10-18 11:35:08 | MASTER- | (21h 24m 39.85s , +40d 38m 56.5s) | C | 60 | 19.6 | Coadd 23440 | 2025-10-18 11:35:53 | MASTER- | (21h 26m 55.46s , +34d 43m 11.4s) | C | 60 | 19.6 | 23514 | 2025-10-18 11:37:06 | MASTER- | (21h 24m 38.44s , +40d 36m 49.8s) | C | 60 | 19.6 | 23586 | 2025-10-18 11:38:19 | MASTER- | (21h 31m 14.78s , +40d 24m 32.2s) | C | 60 | 19.6 | 23659 | 2025-10-18 11:39:32 | MASTER- | (21h 20m 28.45s , +36d 37m 54.8s) | C | 60 | 19.4 | 23810 | 2025-10-18 11:42:03 | MASTER- | (21h 24m 45.36s , +40d 38m 28.6s) | C | 60 | 19.6 | 23959 | 2025-10-18 11:44:31 | MASTER- | (21h 24m 41.51s , +40d 38m 32.1s) | C | 60 | 19.6 | 24033 | 2025-10-18 11:45:46 | MASTER- | (21h 39m 37.95s , +36d 37m 01.8s) | C | 60 | 19.9 | 24113 | 2025-10-18 11:47:06 | MASTER- | (21h 26m 55.34s , +34d 43m 32.1s) | C | 60 | 19.6 | 24186 | 2025-10-18 11:48:19 | MASTER- | (21h 24m 38.56s , +40d 37m 23.4s) | C | 60 | 19.6 | 24261 | 2025-10-18 11:49:34 | MASTER- | (21h 31m 08.05s , +40d 25m 50.0s) | C | 60 | 19.6 | 24335 | 2025-10-18 11:50:47 | MASTER- | (21h 20m 31.98s , +36d 36m 32.3s) | C | 60 | 19.4 | 24673 | 2025-10-18 11:56:25 | MASTER- | (21h 38m 44.90s , +37d 40m 08.5s) | C | 60 | 19.7 | 24746 | 2025-10-18 11:57:39 | MASTER- | (21h 26m 06.59s , +35d 44m 31.8s) | C | 60 | 19.6 | 24911 | 2025-10-18 12:00:24 | MASTER- | (21h 30m 14.16s , +41d 26m 28.4s) | C | 60 | 19.5 | 24992 | 2025-10-18 12:01:44 | MASTER- | (21h 19m 42.75s , +37d 38m 24.3s) | C | 60 | 19.5 | 25296 | 2025-10-18 12:06:48 | MASTER- | (21h 38m 47.62s , +37d 39m 00.3s) | C | 60 | 19.9 | 25372 | 2025-10-18 12:08:04 | MASTER- | (21h 26m 09.90s , +35d 45m 43.2s) | C | 60 | 19.7 | 25618 | 2025-10-18 12:12:11 | MASTER- | (21h 30m 14.23s , +41d 26m 02.8s) | C | 60 | 19.5 | 25692 | 2025-10-18 12:13:25 | MASTER- | (21h 19m 42.14s , +37d 37m 52.9s) | C | 60 | 19.5 | 25916 | 2025-10-18 12:17:08 | MASTER- | (21h 38m 41.75s , +37d 38m 43.9s) | C | 60 | 19.9 | 25989 | 2025-10-18 12:18:21 | MASTER- | (21h 26m 04.07s , +35d 45m 22.4s) | C | 60 | 19.6 | 26238 | 2025-10-18 12:22:30 | MASTER- | (21h 30m 15.89s , +41d 26m 02.0s) | C | 60 | 19.6 | 26312 | 2025-10-18 12:23:45 | MASTER- | (21h 19m 42.33s , +37d 38m 56.0s) | C | 60 | 19.5 | 26642 | 2025-10-18 12:29:15 | MASTER- | (21h 38m 40.69s , +37d 39m 18.2s) | C | 60 | 20.0 | 26716 | 2025-10-18 12:30:28 | MASTER- | (21h 26m 03.39s , +35d 42m 50.9s) | C | 60 | 19.6 | 27298 | 2025-10-18 12:40:11 | MASTER- | (21h 38m 41.77s , +37d 38m 45.3s) | C | 60 | 19.9 | 39779 | 2025-10-18 16:07:11 | MASTER-Kislovodsk | (21h 23m 12.87s , +39d 31m 52.3s) | C | 180 | 18.3 | 39959 | 2025-10-18 16:07:11 | MASTER-Kislovodsk | (21h 23m 12.87s , +39d 31m 52.2s) | C | 540 | 18.6 | Coadd 39779 | 2025-10-18 16:07:11 | MASTER-Kislovodsk | (21h 28m 59.97s , +39d 09m 35.7s) | C | 180 | 18.7 | 39919 | 2025-10-18 16:10:31 | MASTER-Kislovodsk | (21h 29m 03.89s , +41d 25m 46.0s) | C | 60 | 17.5 | 39919 | 2025-10-18 16:10:31 | MASTER-Kislovodsk | (21h 35m 00.82s , +41d 03m 22.0s) | C | 60 | 18.1 | 40059 | 2025-10-18 16:11:51 | MASTER-Kislovodsk | (21h 23m 12.96s , +39d 29m 49.4s) | C | 180 | 18.2 | 40059 | 2025-10-18 16:11:51 | MASTER-Kislovodsk | (21h 29m 00.21s , +39d 07m 33.0s) | C | 180 | 18.6 | 40199 | 2025-10-18 16:15:11 | MASTER-Kislovodsk | (21h 32m 40.41s , +39d 30m 38.4s) | C | 60 | 17.3 | 40199 | 2025-10-18 16:15:11 | MASTER-Kislovodsk | (21h 38m 27.62s , +39d 08m 21.8s) | C | 60 | 17.9 | 40339 | 2025-10-18 16:16:31 | MASTER-Kislovodsk | (21h 23m 15.28s , +39d 31m 25.2s) | C | 180 | 18.2 | 40339 | 2025-10-18 16:16:31 | MASTER-Kislovodsk | (21h 29m 02.86s , +39d 09m 10.0s) | C | 180 | 18.5 | 40706 | 2025-10-18 16:23:38 | MASTER-Kislovodsk | (21h 28m 41.27s , +41d 26m 54.8s) | C | 60 | 17.8 | 40706 | 2025-10-18 16:23:39 | MASTER-Kislovodsk | (21h 34m 56.99s , +41d 04m 17.1s) | C | 60 | 18.4 | 40846 | 2025-10-18 16:24:59 | MASTER-Kislovodsk | (21h 22m 51.36s , +39d 31m 08.1s) | C | 180 | 18.3 | 40846 | 2025-10-18 16:24:59 | MASTER-Kislovodsk | (21h 28m 56.82s , +39d 08m 19.4s) | C | 180 | 18.7 | 40986 | 2025-10-18 16:28:18 | MASTER-Kislovodsk | (21h 32m 12.06s , +39d 32m 51.9s) | C | 60 | 17.7 | 40986 | 2025-10-18 16:28:18 | MASTER-Kislovodsk | (21h 38m 17.80s , +39d 09m 55.3s) | C | 60 | 18.2 | 41126 | 2025-10-18 16:29:38 | MASTER-Kislovodsk | (21h 22m 59.40s , +39d 31m 04.5s) | C | 180 | 18.6 | 41126 | 2025-10-18 16:29:38 | MASTER-Kislovodsk | (21h 29m 05.14s , +39d 07m 57.1s) | C | 180 | 18.9 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42358. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40433] LIGO/Virgo/KAGRA S251018bi: Identification of a GW compact binary merger candidate
by GCN Circulars 18 Oct '25

18 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42357 SUBJECT: LIGO/Virgo/KAGRA S251018bi: Identification of a GW compact binary merger candidate DATE: 25/10/18 16:05:11 GMT FROM: shoki.iwaguchi(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S251018bi during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-10-18 15:25:47.021 UTC (GPS time: 1444836365.021). 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. S251018bi 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: https://gracedb.ligo.org/superevents/S251018bi The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%). Assuming 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%. The source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * amplfi.multiorder.fits,0, an initial localization generated by AMPLFI [9], distributed via GCN and SCiMMA notices about 23 seconds after the candidate event time. * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [10], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,0. For the bayestar.multiorder.fits,0 sky map, the 90% credible region is 1463 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 5450 +/- 1489 Mpc (a posteriori mean +/- standard deviation). For 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/. [1] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010 [2] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004 [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [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 [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [7] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [8] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [9] Chatterjee et al. MLST 5, 045030 (2024) doi:10.1088/2632-2153/ad8982 [10] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/42357. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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