October 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 40554] GRB 251026B: Tentative GOTO optical counterpart candidate
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42470 SUBJECT: GRB 251026B: Tentative GOTO optical counterpart candidate DATE: 25/10/27 10:39:39 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> S. Belkin, G. Ramsay, B. P. Gompertz, D. O’Neill, M. Wortley, R. Starling K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, A. Kumar, M. Pursiainen report on behalf of GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the short GRB 251026B (Fermi GBM team, GCN 42455). Targeted observations were performed beginning at 2025-10-26 17:35:03 UT, (+10.3h post trigger) and continued through to 2025-10-27 05:29:04 UT (+22.2h post trigger). 88 images were taken, across 8 unique pointings, covering 417.8 square degrees within the 90% localisation contour. ~75.1% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.1 mag. Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. We detect a new optical source, GOTO25jgl/AT2025absf, with coordinates: RA,DEC (J2000) = 133.2284, -6.25815 | 08:52:54.8, -06:15:29.4 This position lies on the 38% probability contour of the Fermi/GBM localisation. The source was initially detected with AB magnitude L = 18.45 ± 0.10 mag (+10.3h), before fading to L = 18.80 ± 0.06 mag (+22.2 h). Forced photometry on the difference images indicates excess flux corresponding to L = 19.06 ± 0.28 AB mag at 2025-10-23 18:09:10 (−2.55 d), but visual inspection does not reveal an obvious point source, meaning the marginally significant residual may be due to an imperfect subtraction. Earlier coverage at 2025-10-23 04:48:34 (−3.10 d) yields a 3-sigma upper limit of L > 20.50 AB. The source is coincident with the galaxy LEDA 1034956 with a redshift of z=0.055 (247.26 ± 17.34 Mpc). The two post-trigger detections are consistent with a power-law decay with index: alpha ~0.41. The temporal coincidence and fast decay suggest that GOTO25jgl could be the optical counterpart to GRB 251026B. However, given the possible excess flux observed pre-trigger, we can not definitively rule out that it is an unrelated, fast-evolving transient. Further follow-up to determine the nature of the source is encouraged. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/42470. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40553] GRB 251025C: AstroSat CZTI detection
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42469 SUBJECT: GRB 251025C: AstroSat CZTI detection DATE: 25/10/27 09:48:20 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (IITB), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long, bright GRB 251025C which was also detected by SWIFT BAT (DeLaunay et. al., GCN Circ. 42412), and CALET (Asaoka et. al., GCN Circ. 42414). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-10-25 23:08:37.50 UTC. The measured peak count rate associated with the burst is 201 (+35, -35) counts/s above the background in the combined data of three quadrants (out of four), with a total of 1467 (+193, -175) counts. The local mean background count rate was 216 (+2, -4) counts/s. Using cumulative rates, we measure a T90 of 18.4 (+1.3, -2.4) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-10-25 23:08:37.55 UTC. The measured peak count rate associated with the burst is 475 (+68, -78) counts/s above the background in the combined data of all quadrants, with a total of 3334 (+360, -502) counts. The local mean background count rate was 1311 (+8, -6) counts/s. We measure a T90 of 17.3 (+1.7, -2.0) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/42469. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40552] EP251023a: Mondy optical observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42468 SUBJECT: EP251023a: Mondy optical observations DATE: 25/10/27 09:21:37 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), A. Pozanenko (IKI) , N. Pankov (HSE, IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN: We observed the field of the EP transient EP251023a (Wu et al., GCN 42388) in the R-filter with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy). We observed the field on Oct. 23 and 25, 2025, taking several frames with 120 s exposures. The optical couterpart detected by GOTO (Wortley et al., GCN 42387) and also observed by Li et al., GCN 42389; Liu et al., GCN 42391; Mandarakas et al., GCN 42400; Lipunov et al., GCN 42405; Selezneva et al., GCN 42406; Mohan et al., GCN 42411; Rakotondrainibe et al., GCN 42420; Rajabov et al., 42422, is clearly detected in the stacked frame of the first epoch and is not detected in that of the second one. The preliminary photometry is the following: Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2025-10-23 20:15:41 0.75316 20*120 R 20.64 0.12 22.0 2025-10-25 20:07:45 2.75807 35*120 R n/d n/d 22.7 The photometry is based on several nearby PS1 stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42468. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40551] GRB 251025C: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42467 SUBJECT: GRB 251025C: CALET Gamma-Ray Burst Monitor detection DATE: 25/10/27 05:49:55 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> S. Torii (Waseda U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 251025C (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 42449) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 23:08:37.27 UTC on 25 October 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1445468431/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure that starts at T+2.9 sec, peaks at T+3.5 sec, and ends at T+46.7 sec. The T90 and T50 durations measured by the SGM data are 38.6 +/- 2.6 sec and 15.1 +/- 1.4 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1445468431/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/42467. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40550] GRB 251025B: MAO/AZT-22 optical observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42466 SUBJECT: GRB 251025B: MAO/AZT-22 optical observations DATE: 25/10/27 03:45:44 GMT FROM: Yodgor Rajabov at UBAI <rajabov(a)astrin.uz> Y. Rajabov, B.Abidkhanov, O. Burkhonov, S. Ehgamberdiev, Y. Tillayev (UBAI), A. Shaymanov (Maidanak Observatory/UBAI) report on behalf of UBAI team. We observed the field of the GRB 251025B (Hussein et al., GCN 42437) with the 1.5-m at Maidanak Observatory telescope AZT-22 equipped with the 4kx4k CCD SNUCAM camera (Im et al., 2010). The OT (Wu et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440; Beardmore et al., GCN 42445; Mohan et al., GCN 42447; Hernández Funget al., GCN 42450; Pereyra et al., GCN 42452; Li et al., GCN 42453; Mo et al., GCN 42459; Rakotondrainibe et al., GCN 42460) is clearly detected in the individual and stacked frames. Preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope (nxs) (mid, days) 2025-10-26 19:09:36 6x300 1.19827 R 20.75 0.03 23.10 MAO/AZT-22 All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousins filters were calibrated using the Gaia DR3 Synphot catalog. The data has not corrected for the Galactic extinction. Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42466. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40549] LIGO/Virgo/KAGRA S251026bn: Updated Sky localization
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42465 SUBJECT: LIGO/Virgo/KAGRA S251026bn: Updated Sky localization DATE: 25/10/27 02:40:22 GMT FROM: lucy.thomas(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S251026bn (GCN Circular 42462). 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: https://gracedb.ligo.org/superevents/S251026bn For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 744 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1202 +/- 347 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] 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 View this GCN Circular online at https://gcn.nasa.gov/circulars/42465. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40548] Fermi GRB 251026B: Global MASTER-Net observations report
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42464 SUBJECT: Fermi GRB 251026B: Global MASTER-Net observations report DATE: 25/10/27 01:31:39 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 Fermi GRB 251026B ( Fermi GBM team, GCN 42455) errorbox 59309 sec after notice time and 62633 sec after trigger time at 2025-10-27 00:42:47 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 68 deg. The sun altitude is -32.5 deg. The galactic latitude b = 20 deg., longitude l = 239 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3023975 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 62664 | 2025-10-27 00:42:47 | MASTER-Kislovodsk | (08h 46m 04.47s , -11d 51m 14.2s) | C | 60 | 17.9 | 62664 | 2025-10-27 00:42:47 | MASTER-Kislovodsk | (08h 50m 15.56s , -12d 14m 29.7s) | C | 60 | 18.3 | 63317 | 2025-10-27 00:53:40 | MASTER-Kislovodsk | (08h 46m 04.23s , -11d 50m 49.0s) | C | 60 | 17.8 | 63317 | 2025-10-27 00:53:40 | MASTER-Kislovodsk | (08h 50m 17.20s , -12d 14m 14.5s) | C | 60 | 18.1 | 63959 | 2025-10-27 01:04:22 | MASTER-Kislovodsk | (08h 46m 02.23s , -11d 50m 25.1s) | C | 60 | 18.2 | 63959 | 2025-10-27 01:04:22 | MASTER-Kislovodsk | (08h 50m 16.29s , -12d 13m 53.6s) | C | 60 | 18.4 | 64626 | 2025-10-27 01:15:29 | MASTER-Kislovodsk | (08h 46m 09.08s , -11d 49m 58.6s) | C | 60 | 18.2 | 64626 | 2025-10-27 01:15:29 | MASTER-Kislovodsk | (08h 50m 18.58s , -12d 13m 27.0s) | C | 60 | 18.4 | 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/42464. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40547] Fermi GRB 251025C: Global MASTER-Net observations report
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42463 SUBJECT: Fermi GRB 251025C: Global MASTER-Net observations report DATE: 25/10/27 01:31:01 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 Fermi GRB 251025C ( Fermi GBM team, GCN 42449) errorbox 1 days 5134 sec after notice time and 1 days 5165 sec after trigger time at 2025-10-27 00:34:45 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 53 deg. The sun altitude is -33.9 deg. The galactic latitude b = 58 deg., longitude l = 147 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3023716 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 91596 | 2025-10-27 00:34:45 | MASTER-Kislovodsk | (11h 18m 11.77s , +54d 29m 42.9s) | C | 60 | 18.3 | 91596 | 2025-10-27 00:34:45 | MASTER-Kislovodsk | (11h 25m 08.42s , +54d 06m 43.1s) | C | 60 | 18.5 | 91675 | 2025-10-27 00:36:05 | MASTER-Kislovodsk | (11h 31m 25.80s , +55d 59m 16.1s) | C | 60 | 18.3 | 91675 | 2025-10-27 00:36:05 | MASTER-Kislovodsk | (11h 24m 10.23s , +56d 22m 21.0s) | C | 60 | 18.1 | 91755 | 2025-10-27 00:37:25 | MASTER-Kislovodsk | (11h 20m 02.72s , +52d 12m 24.9s) | C | 60 | 18.6 | 91755 | 2025-10-27 00:37:25 | MASTER-Kislovodsk | (11h 13m 24.71s , +52d 35m 17.4s) | C | 60 | 18.6 | 91835 | 2025-10-27 00:38:45 | MASTER-Kislovodsk | (11h 44m 17.61s , +54d 29m 12.9s) | C | 60 | 18.1 | 91835 | 2025-10-27 00:38:45 | MASTER-Kislovodsk | (11h 51m 11.39s , +54d 06m 05.0s) | C | 60 | 18.3 | 91916 | 2025-10-27 00:40:05 | MASTER-Kislovodsk | (11h 38m 20.05s , +52d 33m 52.5s) | C | 60 | 18.1 | 91996 | 2025-10-27 00:41:25 | MASTER-Kislovodsk | (11h 31m 44.37s , +58d 17m 35.7s) | C | 60 | 18.1 | 91996 | 2025-10-27 00:41:25 | MASTER-Kislovodsk | (11h 39m 22.93s , +57d 54m 25.4s) | C | 60 | 18.3 | 92236 | 2025-10-27 00:45:26 | MASTER-Kislovodsk | (11h 18m 07.62s , +54d 29m 57.0s) | C | 60 | 18.3 | 92236 | 2025-10-27 00:45:26 | MASTER-Kislovodsk | (11h 25m 08.02s , +54d 06m 32.4s) | C | 60 | 18.3 | 92316 | 2025-10-27 00:46:46 | MASTER-Kislovodsk | (11h 24m 08.47s , +56d 22m 38.2s) | C | 60 | 18.1 | 92316 | 2025-10-27 00:46:46 | MASTER-Kislovodsk | (11h 31m 24.36s , +55d 59m 08.8s) | C | 60 | 18.3 | 92396 | 2025-10-27 00:48:06 | MASTER-Kislovodsk | (11h 13m 23.20s , +52d 35m 54.1s) | C | 60 | 18.6 | 92396 | 2025-10-27 00:48:06 | MASTER-Kislovodsk | (11h 20m 01.70s , +52d 12m 36.7s) | C | 60 | 18.6 | 92476 | 2025-10-27 00:49:26 | MASTER-Kislovodsk | (11h 44m 17.35s , +54d 29m 36.7s) | C | 60 | 18.0 | 92476 | 2025-10-27 00:49:26 | MASTER-Kislovodsk | (11h 51m 11.53s , +54d 06m 03.7s) | C | 60 | 18.2 | 92556 | 2025-10-27 00:50:46 | MASTER-Kislovodsk | (11h 38m 19.67s , +52d 34m 11.0s) | C | 60 | 18.2 | 92644 | 2025-10-27 00:52:13 | MASTER-Kislovodsk | (11h 31m 43.71s , +58d 18m 05.9s) | C | 60 | 18.1 | 92644 | 2025-10-27 00:52:13 | MASTER-Kislovodsk | (11h 39m 22.66s , +57d 54m 30.1s) | C | 60 | 18.3 | 92890 | 2025-10-27 00:56:20 | MASTER-Kislovodsk | (11h 18m 04.46s , +54d 30m 35.0s) | C | 60 | 18.3 | 92890 | 2025-10-27 00:56:20 | MASTER-Kislovodsk | (11h 25m 08.64s , +54d 07m 10.4s) | C | 60 | 18.3 | 92970 | 2025-10-27 00:57:40 | MASTER-Kislovodsk | (11h 24m 09.70s , +56d 23m 16.5s) | C | 60 | 18.1 | 92970 | 2025-10-27 00:57:40 | MASTER-Kislovodsk | (11h 31m 27.23s , +55d 59m 48.2s) | C | 60 | 18.1 | 93050 | 2025-10-27 00:58:59 | MASTER-Kislovodsk | (11h 13m 21.24s , +52d 36m 14.7s) | C | 60 | 18.5 | 93050 | 2025-10-27 00:58:59 | MASTER-Kislovodsk | (11h 20m 01.17s , +52d 12m 57.7s) | C | 60 | 18.4 | 93129 | 2025-10-27 01:00:19 | MASTER-Kislovodsk | (11h 44m 15.91s , +54d 29m 56.6s) | C | 60 | 18.1 | 93129 | 2025-10-27 01:00:19 | MASTER-Kislovodsk | (11h 51m 11.44s , +54d 06m 23.7s) | C | 60 | 18.2 | 93210 | 2025-10-27 01:01:40 | MASTER-Kislovodsk | (11h 38m 18.17s , +52d 35m 14.3s) | C | 60 | 18.1 | 93290 | 2025-10-27 01:02:59 | MASTER-Kislovodsk | (11h 31m 44.06s , +58d 18m 37.3s) | C | 60 | 18.2 | 93290 | 2025-10-27 01:02:59 | MASTER-Kislovodsk | (11h 39m 24.39s , +57d 55m 02.7s) | C | 60 | 18.3 | 93533 | 2025-10-27 01:07:03 | MASTER-Kislovodsk | (11h 18m 02.58s , +54d 31m 12.2s) | C | 60 | 18.2 | 93533 | 2025-10-27 01:07:03 | MASTER-Kislovodsk | (11h 25m 08.82s , +54d 07m 52.0s) | C | 60 | 18.3 | 93613 | 2025-10-27 01:08:23 | MASTER-Kislovodsk | (11h 24m 07.26s , +56d 23m 53.1s) | C | 60 | 18.1 | 93613 | 2025-10-27 01:08:23 | MASTER-Kislovodsk | (11h 31m 26.30s , +56d 00m 29.1s) | C | 60 | 18.3 | 93693 | 2025-10-27 01:09:43 | MASTER-Kislovodsk | (11h 13m 21.14s , +52d 37m 05.7s) | C | 60 | 18.6 | 93693 | 2025-10-27 01:09:43 | MASTER-Kislovodsk | (11h 20m 02.47s , +52d 13m 53.0s) | C | 60 | 18.6 | 93793 | 2025-10-27 01:11:23 | MASTER-Kislovodsk | (11h 44m 13.86s , +54d 30m 52.5s) | C | 60 | 18.1 | 93793 | 2025-10-27 01:11:23 | MASTER-Kislovodsk | (11h 51m 10.90s , +54d 07m 24.6s) | C | 60 | 18.1 | 93879 | 2025-10-27 01:12:49 | MASTER-Kislovodsk | (11h 38m 18.19s , +52d 35m 51.5s) | C | 60 | 18.1 | 93959 | 2025-10-27 01:14:09 | MASTER-Kislovodsk | (11h 31m 42.25s , +58d 19m 32.6s) | C | 60 | 18.1 | 93959 | 2025-10-27 01:14:09 | MASTER-Kislovodsk | (11h 39m 23.62s , +57d 56m 04.3s) | C | 60 | 18.4 | 94399 | 2025-10-27 01:21:29 | MASTER-Kislovodsk | (11h 17m 59.49s , +54d 30m 58.7s) | C | 60 | 18.4 | 94399 | 2025-10-27 01:21:29 | MASTER-Kislovodsk | (11h 25m 03.05s , +54d 07m 53.1s) | C | 60 | 18.3 | 94478 | 2025-10-27 01:22:48 | MASTER-Kislovodsk | (11h 24m 10.99s , +56d 25m 08.0s) | C | 60 | 18.2 | 94478 | 2025-10-27 01:22:48 | MASTER-Kislovodsk | (11h 31m 32.09s , +56d 01m 57.7s) | C | 60 | 18.3 | 94558 | 2025-10-27 01:24:08 | MASTER-Kislovodsk | (11h 13m 15.55s , +52d 39m 26.4s) | C | 60 | 18.6 | 94558 | 2025-10-27 01:24:08 | MASTER-Kislovodsk | (11h 19m 58.90s , +52d 16m 26.6s) | C | 60 | 18.5 | 94640 | 2025-10-27 01:25:30 | MASTER-Kislovodsk | (11h 44m 14.15s , +54d 30m 13.3s) | C | 60 | 18.1 | 94640 | 2025-10-27 01:25:30 | MASTER-Kislovodsk | (11h 51m 12.53s , +54d 06m 56.7s) | C | 60 | 18.4 | 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/42463. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40546] LIGO/Virgo/KAGRA S251026bn: Identification of a GW compact binary merger candidate
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42462 SUBJECT: LIGO/Virgo/KAGRA S251026bn: Identification of a GW compact binary merger candidate DATE: 25/10/26 22:11:15 GMT FROM: joan-rene.merou(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S251026bn during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-10-26 21:16:05.296 UTC (GPS time: 1445548583.296). 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. S251026bn is an event of interest because its false alarm rate, as estimated by the online analysis, is 4.8e-12 Hz, or about one in 1e4 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S251026bn The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<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 8%. The source chirp mass falls with highest probability in the bin (5.5, 11.0) 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: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [9], distributed via GCN and SCiMMA notices about 29 seconds after the candidate event time. * 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. The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 956 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1254 +/- 349 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] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/42462. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40545] GRB 251026A: Swift-XRT observations
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42461 SUBJECT: GRB 251026A: Swift-XRT observations DATE: 25/10/26 21:42:15 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source GRB 251026A (SVOM burst-id sb25102605), collecting 1.7 ks of Photon Counting (PC) mode data between T0+5.8 ks and T0+12 ks after the trigger. We have detected 2 sources. These have been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 2 uncatalogued X-ray sources * 0 known X-ray sources We note that neither source is consistent with the SVOM/MXT position given in GCN Circ. 42454. Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J044944.9+514605): ================================== RA (J2000.0): 72.4374 = 04 49 44.98 Dec (J2000.0): +51.7683 = +51 46 05.9 Error: 5.1 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 5.8 arcmin from the SVOM/ECLAIRs position. Mean rate: 0.0123 +/- 0.0033 ct s^-1 Mean flux: (4.6 +/- 1.2)e-13 erg cm^-2 s^-1 Peak rate: 0.0123 +/- 0.0033 ct s^-1 Peak flux: (4.6 +/- 1.2)e-13 erg cm^-2 s^-1 ECF: 3.75e-11 erg cm^-2 ct^-1 assuming NH=1.57e+22 cm^-2, gamma=2.98 determined from a spectral fit. XMM UL: 3.5e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. A SIMBAD object `NVSS J044945+514603' is 7.5" away. There are 2 2MASS objects within the source's 3-sigma error radius. Source 2 (SWIFT J045052.5+515630): ================================== RA (J2000.0): 72.7189 = 04 50 52.54 Dec (J2000.0): +51.9418 = +51 56 30.5 Error: 9.7 (arcsec, radius, 90% confidence). Detect flag: REASONABLE Distance: 9.6 arcmin from the SVOM/ECLAIRs position. Mean rate: (4.0 [+2.6, -1.8])e-3 ct s^-1 Mean flux: (1.74 [+1.10, -0.78])e-13 erg cm^-2 s^-1 Peak rate: (4.0 [+2.6, -1.8])e-3 ct s^-1 Peak flux: (1.74 [+1.10, -0.78])e-13 erg cm^-2 s^-1 XMM UL: 2.3e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. A SIMBAD object `NVSS J045052+515630' is 3.9" away. There are 6 2MASS objects within the source's 3-sigma error radius. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00045. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42461. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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