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

[vsnet-grb-info 40464] EP/WXT 01709247295: GOTO optical afterglow candidate.
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42387 SUBJECT: EP/WXT 01709247295: GOTO optical afterglow candidate. DATE: 25/10/23 08:44:08 GMT FROM: d.s.oneill(a)bham.ac.uk M. E. Wortley, D. O'Neill, G. Ramsay, B. P. Gompertz, B. Godson, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to Einstein Probe alert 01709247295. Serendipitous imaging covered the position at 2025-10-23 05:25:22 (+2.9h post trigger) and targeted observations at 2025-10-23 05:36:01 UT, (+3.08h post trigger). The observations consisted of 4x45s and 4x90s exposures respectively 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. A new optical source, GOTO25ixt, is identified within the WXT 90% localisation region with coordinates: RA,DEC (J2000) =127.134217, 20.86431 | 08:28:32.21, +20:51:51.51 The source was initially detected with magnitude L = 18.57 ± 0.06 AB mag (+2.9h), with marginal fading to L = 18.64 ± 0.04 AB mag (+3.08h). The source was not detected in ATLAS forced photometry (Shingles et al 2021) at 2025-10-22 15:04:55 (11.44 hours pre-trigger), with a 5-sigma limiting magnitude of o > 19.45 AB mag. 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/42387. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40463] GRB 251022A: GOTO optical counterpart detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42386 SUBJECT: GRB 251022A: GOTO optical counterpart detection DATE: 25/10/23 08:26:52 GMT FROM: d.s.oneill(a)bham.ac.uk D. O’Neill, M. Wortley, B. P. Gompertz, R. Starling K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, 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 GRB 251022A (Fermi GBM team, GCN 42380; Di Lalla et al. GCN 42384). Targeted observations were performed beginning at 2025-10-23 00:58:21 UT, (+2.4h post trigger) and continued through to 2025-10-23 05:04:03 UT (+6.5h post trigger). 161 images were taken, across 10 unique pointings, covering 219.8 square degrees within the 90% localisation contour. ~89.9% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.5 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, GOTO25iym, with coordinates: RA,DEC (J2000) = 65.497023, -18.9195 | 04:21:59.29, -18:55:10.19 This position lies on the 92% contour of the Fermi/GBM localisation and is offset by 0.41 degrees from the Fermi/LAT position (90% statistical uncertainty: 0.32 deg; Di Lalla et al., GCN 42384). The source was initially detected with AB magnitude L = 18.21 ± 0.03 mag (+2.4h), before fading to L = 18.82 ± 0.06 mag (+4.67h). We find no evidence of this source prior to the GRB trigger time in the previous GOTO observation taken at 2025-10-22 14:20:35 UT (8.23h pre-trigger) down to a 5-sigma depth of L > 19.54 AB mag. Despite the mild inconsistency with the Fermi/LAT position, which may be explained by the unaccounted-for systematic uncertainty, the power-law decay seen across three epochs combined with the recent deeper non-detection at the position pre-GRB strongly suggest that GOTO25iym is the afterglow of GRB 251022A. 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/42386. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40462] GRB 251023A: Fermi GBM Final Localization Correction
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42385 SUBJECT: GRB 251023A: Fermi GBM Final Localization Correction DATE: 25/10/23 07:33:17 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> The Fermi GBM team reports the detection of a likely LONG GRB "At 05:57:43.66 UT on 23 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251023A (trigger 782891868/251023248). This trigger was initially classified as distant particles by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 39.87, Dec = -6.53 (J2000 degrees, equivalent to J2000 02h 39m, -06d 31'), with a statistical uncertainty of 3.12 degrees. The angle from the Fermi LAT boresight is 89 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251023248/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251023248/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251023248/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/42385. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40461] GRB 251022A: Fermi-LAT detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42384 SUBJECT: GRB 251022A: Fermi-LAT detection DATE: 25/10/23 07:29:47 GMT FROM: Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi(a)ba.infn.it> N. Di Lalla (Stanford Univ.), D. Kocevski (NASA/MSFC), N. Omodei (Stanford Univ.), S. Cutini (INFN Perugia) A. Holzmann Airasca (UniTrento and INFN Bari), F. Longo (University and INFN, Trieste) and E. Bissaldi (Politecnico and INFN Bari) report on behalf of the Fermi-LAT Collaboration: On October 22, 2025, Fermi-LAT detected high-energy emission from GRB 251022A, which was also detected by Fermi-GBM (trigger 782865260 / 251022940, GCN 42380). The best LAT on-ground location is found to be: RA, Dec = 65.38, -19.31 (J2000) with an error radius of 0.32 deg (90 % containment, statistical error only). This was 36 deg from the LAT boresight at the time of the GBM trigger (T0 = 22:34:15.26 UT). The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0 - 300 s after the GBM trigger is (5.4 ± 2.0) E-6 ph/cm2/s. The estimated photon index above 100 MeV is -2.5 ± 0.5. The highest-energy photon is a 2 GeV event which is observed ~ 71 seconds after the GBM trigger. A Swift ToO has been approved for this burst. The Fermi-LAT point of contact for this burst is Sara Cutini (sara.cutini(a)pg.infn.it) The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/42384. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40460] GRB 251016B: Fermi GBM Detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42383 SUBJECT: GRB 251016B: Fermi GBM Detection DATE: 25/10/23 06:22:48 GMT FROM: Matt Godwin <msg0028(a)uah.edu> Matt Godwin (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 23:59:00.72 UT on 16 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251016B (trigger 782351945/251016999). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 183.64, Dec = 59.60 (J2000 degrees, equivalent to J2000 12h 14m, +59d 36'), with a statistical uncertainty of 1.00 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 46 degrees. The GBM light curve consists of a single bright emission episode with a duration (T90) of about 7.1 s (50-300 keV). The time-averaged spectrum from T0-0.8 to T0+13.5 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.07 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 310 +/- 1 keV. The event fluence (10-1000 keV) in this time interval is (2.27 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2.4 s in the 10-1000 keV band is 37.5 +/- 0.5 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 222 +/- 1 keV, alpha = -0.96 +/- 0 and beta = -2 +/- 0.01. 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/42383. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40459] GRB 251022A: Tiled Swift observations
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42382 SUBJECT: GRB 251022A: Tiled Swift observations DATE: 25/10/23 05:56:57 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a series of observations, tiled on the sky, of the Fermi/LAT GRB 251022A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/xrt_products/TILED_GRB00139 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. The probability of finding serendipitous sources, unrelated to the Fermi/LAT event is high: any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42382. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40458] LAT GRB251022.94: Global MASTER-Net observations report
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42381 SUBJECT: LAT GRB251022.94: Global MASTER-Net observations report DATE: 25/10/23 03:11:21 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) was pointed to the LAT GRB251022.94 (trigger No 782865260,04h 21m 31.18s , -19d 18m 35.6s, R=0.32) errorbox 13 sec after notice time and 16215 sec after trigger time at 2025-10-23 03:04:30 UT, with upper limit up to 17.2 mag. Observations started at twilight. The observations began at zenith distance = 32 deg. The sun altitude is -10.1 deg. The galactic latitude b = -41 deg., longitude l = 216 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3021522 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 16245 | 2025-10-23 03:04:30 | MASTER-SAAO | (04h 21m 02.62s , -19d 31m 07.4s) | C | 60 | 17.2 | 16245 | 2025-10-23 03:04:30 | MASTER-SAAO | (04h 19m 05.26s , -19d 15m 42.2s) | P\ | 60 | 16.7 | 16324 | 2025-10-23 03:05:49 | MASTER-SAAO | (04h 21m 02.39s , -19d 31m 03.5s) | C | 60 | 16.7 | 16324 | 2025-10-23 03:05:49 | MASTER-SAAO | (04h 19m 05.05s , -19d 15m 37.8s) | P\ | 60 | 16.6 | 16404 | 2025-10-23 03:07:08 | MASTER-SAAO | (04h 19m 04.85s , -19d 15m 33.5s) | P\ | 60 | 16.6 | 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/42381. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40457] GRB 251022A: Fermi GBM Final Real-time Localization
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42380 SUBJECT: GRB 251022A: Fermi GBM Final Real-time Localization DATE: 25/10/22 22:44:50 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 22:34:15 UT on 22 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251022A (trigger 782865260.264246 / 251022940). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 74.5, Dec = -22.7 (J2000 degrees, equivalent to J2000 04h 58m, -22d 41'), with a statistical uncertainty of 1.9 degrees. The angle from the Fermi LAT boresight is 29.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251022940/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251022940/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251022940/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42380. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40456] GRB 251013C: SAO RAS optical observations
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42230 SUBJECT: GRB 251013C: SAO RAS optical observations DATE: 25/10/13 21:31:40 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin, O. I. Spiridonova, V. V. Vlasyuk (SAO RAS), N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Ghosh, S. Razzaque (CAPP, University of Johannesburg), Tao An and Yuanqi Liu (Shanghai Astronomical Observatory) report on behalf of GRB follow-up collaboration and IKI-GRB-FuN. We observed the field of the GRB 251013C (The Fermi GBM team, GCN 42221; Rakotondrainibe et al., GCN 42222) with the 1-m SAO RAS telescope Zeiss-1000 equipped with the CCD-photometer. The observations started on 2025.10.13T19:47:54 UT (t_mid - T0 = 2.1369 hours). The OT (Palmerio et al., GCN 42223; Perez-Garcia et al., GCN 42225; Konno et al., GCN 42226; Martin-Carrillo et al., GCN 42227; Masi, GCN 42228; Palmerio et al, GCN 42229) is clearly detected in the individual images with the following brightness. Date UT start t-T0 Exp. Filter OT Err. (mid, d) (s) 2025.10.13 19:47:54 0.09078 300 Rc 15.84 +/- 0.01 2025.10.13 20:04:02 0.10082 100 Rc 16.05 +/- 0.01 2025.10.13 20:15:34 0.10883 100 Rc 16.21 +/- 0.01 Preliminary photometry is based on the nearby SDSS objects (magnitudes converted with Lupton 2005 equations) and has not corrected for the Galactic extinction. The observations with the 1-m telescope in BVRI filters and also with the 0.5-m telescope AS-500/2 are ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/42230. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40455] GRB 251021A/EP251021b: Fermi-GBM Sub-Threshold Detection
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42379 SUBJECT: GRB 251021A/EP251021b: Fermi-GBM Sub-Threshold Detection DATE: 25/10/22 13:56:22 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (Radboud Univ.), E. Burns (LSU), and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial and temporal coverage of the transient EP251021b detected by EP-WXT (Dai et al., GCN 42377). There was no Fermi-GBM onboard trigger around the EP starting time at T0=2025-10-21T14:28:05 UTC. The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+500] s from the EP T0. A transient was found most significantly at ~T0+7 s on a 4.096 s timescale, with a false alarm rate of 4.9e-05 Hz. The localization is consistent with the EP one, with a spatial association probability of 99.2%. Among the three spectral templates tested, the transient was best-fit with a "soft" spectrum (i.e., a Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/42379. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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