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

[vsnet-grb-info 40114] GRB 250930A: Fermi GBM Final Localization
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42044 SUBJECT: GRB 250930A: Fermi GBM Final Localization DATE: 25/10/01 17:22:07 GMT FROM: Eva MP <eva.palafox(a)gmail.com> The Fermi GBM team reports the detection of a likely LONG GRB "At 20:59:58.57 UT on 30 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250930A (trigger 780958803/250930875). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 336.97, Dec = -44.97 (J2000 degrees, equivalent to J2000 22h 27m, -44d 58'), with a statistical uncertainty of 3.27 degrees. The angle from the Fermi LAT boresight is 109 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250930875/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250930875/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250930875/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/42044. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40113] GRB 251001B: LCOGT Optical Observations
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42043 SUBJECT: GRB 251001B: LCOGT Optical Observations DATE: 25/10/01 15:44:16 GMT FROM: Robert Strausbaugh at Eastern Illinois University <rstrausbaugh(a)eiu.edu> R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the Swift GRB 251001B field (Beardmore et al., GCN 42039) with the LCOGT 1-meter Sinistro instrument at the Siding Spring Observatory, Australia site, on October 1, from 14:51 to 15:23 UT (corresponding to 0.57 to 1.10 hours after the GRB trigger time) with the SDSS i and r filters. We performed a series of 3x300s exposures in i-band and r-band. We detect an uncatalogued source consistent with other optical counterpart observations (Gompertz et al., GCN 42040; An et al., GCN 42041) in both bands. We note that our r-band measurement implies a rapidly fading source. The following magnitudes are calculated using the PanSTARRS catalog as reference: r = 20.26 +/- 0.04 i = 19.81 +/- 0.03 These magnitudes are not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42043. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40112] GRB 250930A: SVOM/GRM observation
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42042 SUBJECT: GRB 250930A: SVOM/GRM observation DATE: 25/10/01 15:31:52 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang. Wen-Jun Tan, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Daigne (IAP), Frédéric Piron (LUPM), Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 250930A (SVOM trigger reference: sb25093008) at 2025-09-30T21:00:23.000 UTC (T0), which is also detected by Fermi/GBM (TrigNum#780960200). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 49 +8/-6 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250930A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 341.57, DEC= -47.95, TrigNum#780958803), is located at about 58 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, but this burst is still marginally detected by ECLAIRs above 50 keV. With this localization, the time-averaged spectrum from T0-37 to T0+24 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.13 +/-0.14 and the cutoff energy, parameterized as Epeak, is 107 +17/-12 keV. The event fluence (10-1000 keV) in this time interval is (8.58 +0.69/-0.57)E-06 erg/cm^2. The localization of GRB 250930A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb250930A_amati.png 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42042. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40111] GRB 251001B: TRT optical afterglow detection and potential host galaxy
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42041 SUBJECT: GRB 251001B: TRT optical afterglow detection and potential host galaxy DATE: 25/10/01 15:17:04 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> J. An, X. Liu (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Q. Jiang, L.B. He, Z.P. Zhu, D. Xu (NAOC), S.Y. Fu (HUST) report on behalf of a large collaboration: We observed the field of GRB 251001B detected by Swift/BAT (Beardmore et al., GCN 42039), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). A series of images were obtained in the R band. A varying optical transient (OT) is detected within the Swift/XRT error circle at coordinates R.A. (J2000) = 2:50:36.33 Dec.(J2000) = -23:01:11.96 with an uncertainty of ~ 0.6 arcsec. It has R ~ 18.9 mag at 21.1 min after the Swift/BAT trigger. We thus think the OT is the optical afterglow of the burst. We also note that there is a galaxy at the OT position from Legacy Survey DR10 with g ~ 25.16, r ~ 24.93, i ~25.06, z ~24.79, and a phot_z ~ 1.14 +/- 0.53, which is presumably the host galaxy of the burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/42041. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40110] GRB 251001B: GOTO optical counterpart detection
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42040 SUBJECT: GRB 251001B: GOTO optical counterpart detection DATE: 25/10/01 15:09:24 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> B. P. Gompertz, D. O'Neill, R. Starling, M. Kennedy, B. Godson, J. Lyman, K. Ackley, M. J. Dyer, K. Ulaczyk, A. Kumar, G. Ramsay, 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 observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 251001B (Fermi GBM team, GCN 42038; Beardmore et al. GCN 42039). Targeted observations were performed at 2025-10-01 14:33:37 (starting 16.3 minutes after trigger). 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. At a position consistent with the Swift/XRT localisation, we detect a new optical source, GOTO25icy, with L = 19.33 ± 0.12 AB mag, at coordinates: RA,DEC (J2000) = 42.651328, -23.02001 | 02:50:36.32, -23:01:12.03 We find no evidence of this source prior to the GRB trigger time in the previous GOTO observation taken at 2025-10-01 14:01:01 UT (16.3 min pre-trigger) down to a 3-sigma depth of L > 20.1 AB mag. We note the source is coincident (~0.4”) with a faint g~25 AB mag source in Legacy Survey DR10, which may be the host galaxy of the GRB. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Observations are ongoing. 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/42040. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40109] GRB 251001B: Swift detection of a burst
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42039 SUBJECT: GRB 251001B: Swift detection of a burst DATE: 25/10/01 14:44:42 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> A. P. Beardmore (U Leicester), J. A. Kennea (PSU), M. J. Moss (GSFC) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 14:17:20 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251001B (trigger=1400467). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 42.665, -23.020 which is RA(J2000) = 02h 50m 40s Dec(J2000) = -23d 01' 09" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of about 25 sec. The peak count rate was ~2,000 counts/sec (15-350 keV), at ~4 sec after the trigger. The XRT began observing the field at 14:19:17.0 UT, 116.5 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 42.65098, -23.02014 which is equivalent to: RA(J2000) = 02h 50m 36.24s Dec(J2000) = -23d 01' 12.5" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 46 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 2.65 x 10^20 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of nominal 150.000 seconds with the White filter starting 860 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. Data from the 2.7'x2.7' sub-image are not available at this time. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.023. Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42039. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40108] GRB 251001B: Fermi GBM Final Real-time Localization
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42038 SUBJECT: GRB 251001B: Fermi GBM Final Real-time Localization DATE: 25/10/01 14:28:02 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 14:17:19 UT on 1 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251001B (trigger 781021044.051374 / 251001595). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 52.0, Dec = -11.2 (J2000 degrees, equivalent to J2000 03h 28m, -11d 11'), with a statistical uncertainty of 5.6 degrees. The angle from the Fermi LAT boresight is 67.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251001595/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251001595/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251001595/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42038. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40107] GRB 251001A: Fermi GBM Detection
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42037 SUBJECT: GRB 251001A: Fermi GBM Detection DATE: 25/10/01 14:15:23 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova (MUNI), S. Lesage (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 02:40:56.95 UT on 01 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251001A (trigger 780979261/251001112). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 224.44, Dec = -56.23 (J2000 degrees, equivalent to J2000 14h 57m, -56d 13'), with a statistical uncertainty of 1.79 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 116 degrees. The GBM light curve consists of two peaks with a duration (T90) of about 7 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+8.640 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.63 +/- 0.08 and the cutoff energy, parameterized as Epeak, is 138 +/- 7 keV. The event fluence (10-1000 keV) in this time interval is (4.4 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+6.0 s in the 10-1000 keV band is 24.8 +/- 0.6 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/42037. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40106] GRB 250910A / EP250910a: VLT limits on the possible associated supernova
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42036 SUBJECT: GRB 250910A / EP250910a: VLT limits on the possible associated supernova DATE: 25/10/01 12:16:53 GMT FROM: Ben Rayson at University of Leicester <br155(a)leicester.ac.uk> N. Habeeb (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), B. Rayson (U. Leicester), N. R. Tanvir (U. Leicester), report on behalf of the Stargate collaboration: We obtained late-time imaging of the GRB 250910A / EP250910a field (Schneider et al., GCN 41794; Li et al., GCN 41798; see also Ma et al., GCN 41769; Liu et al., GCN 41776; Hubert et al., GCN 41842) at z = 0.592 (Saccardi et al., GCN 42031) with the ESO VLT equipped with FORS2. Observations were carried out on 2025 Oct 1.16 UT, i.e. ~21 days after the trigger, in the z and R bands. At the position of the reported afterglow/NIR counterpart we detect a source in both filters. From photometry we measure z = 23.19 ± 0.11 (AB) and r = 23.97 ± 0.10 (AB) calibrated against nearby SkyMapper stars and not corrected for Galactic extinction (which is small, A_V = 0.05 mag). We note that a source is clearly visible at this location in the Legacy Survey images with magnitudes of z = 23.10 ± 0.20 and r = 23.73 ± 0.10 (both in AB). Within the present uncertainties and allowing for filter differences, the fluxes are consistent with the pre-existing host-galaxy brightness. Using SN1998bw as the canonical GRB-SN template, the expected associated SN would have a magnitude of z ~ 22.8 at this epoch, implying a total host+SN flux of z ~ 22.2, which is not observed in this case. We therefore find no evidence for an optically bright SN associated with GRB 250910A / EP250910a at ~21 days post-burst (~13 days in the rest frame). The lack of an additional component on top of the host galaxy suggests that the expected SN emission would need to have approximately z < 24.1, corresponding to a SN ~3x fainter than SN1998bw. Without additional epochs for accurate template subtraction, at this moment, we cannot confirm if GRB 250910A / EP250910a truly lacks an associated SN component or if it simply suffers from some extinction. We acknowledge excellent support from the ESO staff in Paranal, in particular Abel de Burgo Sierra and Cecilia Bustos. View this GCN Circular online at https://gcn.nasa.gov/circulars/42036. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40105] GRB 251001A: BALROG localization (Fermi Trigger 780979261 / GRB 251001112)
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42035 SUBJECT: GRB 251001A: BALROG localization (Fermi Trigger 780979261 / GRB 251001112) DATE: 25/10/01 04:34:51 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 780979261 at 02:40:56 on 01 Oct. 2025 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 227.4 deg Decl.(2000.0) = -57.5 deg The 1 sigma statistical error radius is 2.5 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB251001112/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB251001112/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB251001112/json View this GCN Circular online at https://gcn.nasa.gov/circulars/42035. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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