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

[vsnet-grb-info 40470] EP251021b/GRB 251021A: SVOM/VT optical candidate
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42393 SUBJECT: EP251021b/GRB 251021A: SVOM/VT optical candidate DATE: 25/10/23 10:18:34 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H.L. Li , L.P. Xin, Y. L. Qiu, C. Wu, Y.N. Ma, Z.H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observation to the field of EP251021b/GRB 251021A (Dai et al., GCN 42377; Ravasio et al., GCN 42379). The observation stared at 2025-10-22T20:09:33 UTC, I.e., 29.69 hours post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. Within the error box of EP-FXT (Dai et al., GCN 42377), an uncatalogued source was detected, compared to the Legacy survey DR9 catalog. The position is at R.A., Dec. = 306.745094, -38.3034732 degrees, equivalent to: R.A. (J2000) = 20:26:58.82 Dec. (J2000) = -38:18:12.50 with an uncertainty of 0.5 arcsec. The candidate's magnitudes are given below: Mid_time Band Exposure Time Magnitude (AB) 30.75 hour VT_B 45*70 sec 23.62+/-0.25 mag 30.75 hour VT_R 54*70 sec 22.80+/-0.20 mag Our photometry was derived in AB magnitude and not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/42393. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40469] GRB 251023B / MAXI J0451+122: MAXI/GSC detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42392 SUBJECT: GRB 251023B / MAXI J0451+122: MAXI/GSC detection DATE: 25/10/23 10:08:49 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> C. Kang (Ehime U.), M. Nakajima (Nihon U.), Y. Kawakubo (AGU), H. Negoro, K. Takagi, H. Takahashi, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, T. Nakamoto (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U) report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 08:49:03 UT on October 23, 2025. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (72.930 deg, 12.205 deg) = (04 51 43, +12 12 18) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.15 deg and 0.13 deg, respectively. The roll angle of long axis from the north direction is 71.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 341 +- 36 mCrab (4.0-10.0keV, 1 sigma error). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (72.360, 11.893) deg = (04 49 26, +11 53 34) (J2000) (72.539, 11.711) deg = (04 50 09, +11 42 39) (J2000) (73.436, 12.551) deg = (04 53 44, +12 33 03) (J2000) (73.256, 12.734) deg = (04 53 01, +12 44 02) (J2000) There was no significant excess flux in the previous transit at 07:16 UT with an upper limit of 20 mCrab for each. View this GCN Circular online at https://gcn.nasa.gov/circulars/42392. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40468] EP251023a: NOT optical counterpart detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42391 SUBJECT: EP251023a: NOT optical counterpart detection DATE: 25/10/23 10:01:31 GMT FROM: liuxing(a)nao.cas.cn X. Liu, Z.P. Zhu, L.B. He, J. An, S.Q. Jiang, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), Niko Pyykkinen (NOT) report on behalf of a large collaboration: We observed the field of the EP251023a (Wu et al., GCN 42388) using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observation started at 05:55:11 UTC on 2025-10-23, i.e., 3.4 hours after the EP trigger, and a series of frames were obtained in the Sloan r- and z- bands. Within the EP/FXT localization error region (Wu et al., GCN 42388), the optical counterpart (Wortley et al., GCN 42387; Li et al., GCN 42389) is also clearly detected in both r- and z- bands with magnitudes as follows: T-mid (hr) | Filter | Exposure | Mag 3.49 | r | 3x200s | 18.57 +- 0.01 3.72 | z | 5x150s | 18.36 +- 0.01 calibrated against nearby Pan-STARRS stars and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42391. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40467] Fermi GRB 251023A: Global MASTER-Net observations report
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42390 SUBJECT: Fermi GRB 251023A: Global MASTER-Net observations report DATE: 25/10/23 09:15:24 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 251023A ( Fermi GBM team, GCN 42385) errorbox 665 sec after notice time and 686 sec after trigger time at 2025-10-23 06:09:10 UT, with upper limit up to 20.7 mag. The observations began at zenith distance = 29 deg. The sun altitude is -40.0 deg. The galactic latitude b = -56 deg., longitude l = 180 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3021658 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 717 | 2025-10-23 06:09:10 | MASTER-OAFA | (02h 36m 41.44s , -06d 42m 24.3s) | C | 60 | 20.6 | 792 | 2025-10-23 06:10:25 | MASTER-OAFA | (02h 36m 48.65s , -06d 42m 09.1s) | C | 60 | 20.6 | 880 | 2025-10-23 06:11:53 | MASTER-OAFA | (02h 51m 27.06s , -04d 47m 02.9s) | C | 60 | 20.4 | 956 | 2025-10-23 06:13:09 | MASTER-OAFA | (02h 51m 25.90s , -04d 46m 08.3s) | C | 60 | 20.4 | 1045 | 2025-10-23 06:14:38 | MASTER-OAFA | (02h 29m 25.20s , -08d 34m 50.8s) | C | 60 | 20.3 | 1120 | 2025-10-23 06:15:53 | MASTER-OAFA | (02h 37m 24.96s , -08d 34m 57.2s) | C | 60 | 20.4 | 1197 | 2025-10-23 06:17:10 | MASTER-OAFA | (02h 29m 18.79s , -08d 34m 44.5s) | C | 60 | 20.3 | 1272 | 2025-10-23 06:18:25 | MASTER-OAFA | (02h 37m 30.89s , -08d 35m 06.2s) | C | 60 | 20.4 | 1353 | 2025-10-23 06:19:46 | MASTER-OAFA | (02h 44m 42.03s , -08d 34m 33.8s) | C | 60 | 20.6 | 1429 | 2025-10-23 06:21:02 | MASTER-OAFA | (02h 52m 48.50s , -08d 32m 57.2s) | C | 60 | 20.5 | 1503 | 2025-10-23 06:22:16 | MASTER-OAFA | (02h 44m 48.52s , -08d 34m 42.6s) | C | 60 | 20.7 | 1579 | 2025-10-23 06:23:32 | MASTER-OAFA | (02h 52m 49.17s , -08d 35m 05.7s) | C | 60 | 20.4 | 1654 | 2025-10-23 06:24:47 | MASTER-OAFA | (02h 44m 47.30s , -08d 35m 42.7s) | C | 60 | 20.6 | 1733 | 2025-10-23 06:26:07 | MASTER-OAFA | (02h 52m 04.95s , -06d 40m 17.4s) | C | 60 | 20.2 | 1895 | 2025-10-23 06:28:48 | MASTER-OAFA | (02h 51m 58.29s , -06d 40m 20.1s) | C | 60 | 20.2 | 1981 | 2025-10-23 06:30:14 | MASTER-OAFA | (02h 30m 14.33s , -10d 30m 32.8s) | C | 60 | 20.2 | 2057 | 2025-10-23 06:31:30 | MASTER-OAFA | (02h 38m 20.88s , -10d 28m 16.3s) | C | 60 | 20.5 | 2132 | 2025-10-23 06:32:45 | MASTER-OAFA | (02h 38m 22.92s , -10d 28m 22.0s) | C | 60 | 20.4 | 2215 | 2025-10-23 06:34:08 | MASTER-OAFA | (02h 59m 21.23s , -06d 41m 00.5s) | C | 60 | 20.0 | 2369 | 2025-10-23 06:36:42 | MASTER-OAFA | (02h 59m 20.42s , -06d 42m 09.2s) | C | 60 | 20.1 | 3339 | 2025-10-23 06:52:52 | MASTER-OAFA | (02h 39m 52.78s , -06d 23m 46.0s) | C | 60 | 19.5 | 3405 | 2025-10-23 06:53:58 | MASTER-OAFA | (02h 39m 52.75s , -06d 23m 44.1s) | C | 60 | 19.5 | 3470 | 2025-10-23 06:55:03 | MASTER-OAFA | (02h 39m 52.71s , -06d 23m 42.5s) | C | 60 | 19.6 | 3536 | 2025-10-23 06:56:09 | MASTER-OAFA | (02h 39m 52.68s , -06d 23m 41.2s) | C | 60 | 20.6 | 3601 | 2025-10-23 06:57:15 | MASTER-OAFA | (02h 39m 52.66s , -06d 23m 39.7s) | C | 60 | 20.6 | 3667 | 2025-10-23 06:58:20 | MASTER-OAFA | (02h 39m 52.65s , -06d 23m 38.5s) | C | 60 | 20.6 | 3734 | 2025-10-23 06:59:27 | MASTER-OAFA | (02h 39m 52.64s , -06d 23m 37.5s) | C | 60 | 20.6 | 3800 | 2025-10-23 07:00:33 | MASTER-OAFA | (02h 39m 52.62s , -06d 23m 36.4s) | C | 60 | 20.5 | 3865 | 2025-10-23 07:01:38 | MASTER-OAFA | (02h 39m 52.61s , -06d 23m 35.4s) | C | 60 | 20.5 | 3931 | 2025-10-23 07:02:44 | MASTER-OAFA | (02h 39m 52.60s , -06d 23m 34.4s) | C | 60 | 20.4 | 3997 | 2025-10-23 07:03:50 | MASTER-OAFA | (02h 39m 52.60s , -06d 23m 33.5s) | C | 60 | 20.5 | 4063 | 2025-10-23 07:04:56 | MASTER-OAFA | (02h 39m 52.59s , -06d 23m 32.6s) | C | 60 | 20.6 | 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/42390. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40466] EP251023a: GSP Optical Counterpart Detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42389 SUBJECT: EP251023a: GSP Optical Counterpart Detection DATE: 25/10/23 09:13:54 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> W. X. Li, S. J. Xue (NAOC); M. Andrews, J. Farah, D. A. Howell, M. Newsome, E. Padilla Gonzalez, C. McCully, and G. Terreran (Las Cumbres Observatory), on behalf of a larger collaboration, report optical follow-up observations of EP251023a (Wu et al. GCN 42388) obtained with a Las Cumbres Observatory (LCO) 1-m telescope at Teide Observatory, Tenerife, ~3.6 hours after the EP-WXT trigger. We acquired 2 × 300 s exposures using the broad optical w band. The optical counterpart reported by Wortley et al. (GCN 42387) is detected. Preliminary photometry, calibrated to the r band, yields r ≈ 18.5 mag (not corrected for Galactic extinction). No known source is found at this position in the MPC or other major catalogs. These observations were taken as part of the Global Supernova Project (GSP). View this GCN Circular online at https://gcn.nasa.gov/circulars/42389. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40465] EP251023a: Einstein Probe detection of an X-ray transient
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42388 SUBJECT: EP251023a: Einstein Probe detection of an X-ray transient DATE: 25/10/23 09:11:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wu (NJU), D. F. Hu (PMO, CAS), H. N. Yang, T. Zhao, W. D. Zhang (NAO, CAS), on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251023a. The transient triggered EP-WXT (ID: 01709247295) at 2025-10-23T02:31:09 (UTC). The WXT position of the source is R.A. = 127.151 deg, Dec. = 20.871 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). We performed a Target-of-Opportunity observation with the Follow-up X-ray Telescope on board EP. The observation began at 2025-10-23T07:44:08 (UTC).An uncatalogued X-ray source was detected within the WXT error circle at R.A. = 127.1368 deg, Dec. = 20.8634 deg (J2000), with a positional uncertainty of 20 arcsec in radius (90% confidence level, including both statistical and systematic uncertainties). The source is spatially consistent with the counterpart reported in optical bands (Wortley et al. GCN 42387). Further information will be updated when the telemetry data is received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/42388. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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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