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[vsnet-grb-info 40195] GRB 251005C
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42127 SUBJECT: GRB 251005C DATE: 25/10/06 18:04:22 GMT FROM: Massine El Kabir <m.elkabir(a)campus.unimib.it> GRB 251005C: VLT/X-shooter Imaging Muskan Yadav (U Rome), Yu-Han Yang (U Rome), Massine El Kabir (U Rome), Niccolò Passaleva (U Rome), Eleonora Troja (U Rome) report on behalf of the ERC BHianca team: We observed the field of GRB 251005C (K. L. Page et al., GCN 42113) with the Xshooter spectrograph on the ESO VLT UT3 (Melipal). Observations began at T+16.5 hours. We obtained a total exposure of 335 s using the acquisition and guiding (A&G) camera. Observations were carried out in the i’ filter at an average airmass of about 1.4 and seeing 0.75 arcsec. Within the XRT error region (Goad et al., GCN 42116) we detect a faint (i~24 AB mag) source at coordinates RA, Dec (J2000) = 05:02:44.03, +16:52:51.632. The object appears extended in our images. We also detect the SVOM/VT optical candidate (J. T. Palmeiro et al., GCN 42123) at a significantly fainter magnitude (i~24 AB mag), confirming its rapid fading. We thus suggest that this is the GRB optical counterpart. We thank the staff at the VLT, for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/42127. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40194] GRB 251003A: LAST optical observations
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42126 SUBJECT: GRB 251003A: LAST optical observations DATE: 25/10/06 17:54:49 GMT FROM: Ruslan Konno at Weizmann Institute of Science <ruslankonno(a)gmail.com> R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), and S. Spitzer (WIS) on behalf of the LAST Collaboration We report observations of GRB 251003A, detected by Fermi (Fermi team, GCNC 42069) and Swift (Beardmore et al., GCNC 42070), with the Large Array Survey Telescope (LAST; Ofek et al. 2023 PASP 135, 5001; Ben-Ami et al. 2023 PASP 135, 5002). We observe the field of GRB 251003A using 4 divergent telescopes, each with a FoV of 7.4 deg^2 and no filter (clear - similar to the GAIA Bp band) over several epochs. In each epoch, we coadd 20 images with each of 20s exposure. We detect a faint source coincident with the optical counterpart reported by Aceituno et al., GCN 42072; Méndez et al., GCN 42073; Strausbaugh et al., GCN 42074; Freeberg et al., GCN 42085; Sanchez-Ramirez et al., GCN 42086; Worssam et al., GCN 42094; Schneider et al., GCN 42095; Mo et al., GCN 42106. The earliest detection with a 20x20s exposure image is confirmed at 2025-10-03 02:03:10 UTC (T-T0=280s) at an AB magnitude of 19.60 +/- 0.08. LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42126. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40193] GRB 251002A: LAST optical observations
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42125 SUBJECT: GRB 251002A: LAST optical observations DATE: 25/10/06 16:43:55 GMT FROM: Ruslan Konno at Weizmann Institute of Science <ruslankonno(a)gmail.com> R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), and S. Spitzer (WIS) on behalf of the LAST Collaboration We report observations of GRB 251002A (Saccardi et al. GCN 42060), detected by SVOM, with the Large Array Survey Telescope (LAST; Ofek et al. 2023 PASP 135, 5001; Ben-Ami et al. 2023 PASP 135, 5002). We observe the field of GRB 251002A using 4 divergent telescopes, each with a FoV of 7.4 deg^2 and no filter (clear - similar to the GAIA Bp band) over several epochs. In each epoch, we coadd 20 images with each of 20s exposure. We clearly detect the optical counterpart reported by Palmerio et al. GCN 42061; Turpin et. al, GCN 42062; Jelinek et. al, GCN 42063; Juliá-Maroto et. al, GCN 42064; Moskvitin et. al, GCN 42065; Perez-Garcia et. al, GCN 42066; Saccardi et. al, GCN 42076; Mandarakas et. al, GCN 42077; Cao et. al, GCN 42078; Schneider et. al, GCN 42080; Pankov et. al, GCN 42081; Leonini et. al, GCN 42082; Odeh et. al, GCN 42087; Wortley et. al, GCN 42091; Shilling, GCN 42099; Calapai & Giorgio, GCN 42101; Pankov et. al, GCN 42110. The earliest detection with a 20x20s exposure image is confirmed at 2025-10-02 20:48:23 UTC (T-T0=0.55h) at an AB magnitude of 18.53 +/- 0.05. LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42125. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40192] GRB 251006A: Fermi GBM Final Real-time Localization
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42124 SUBJECT: GRB 251006A: Fermi GBM Final Real-time Localization DATE: 25/10/06 13:38:08 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 SHORT GRB At 13:27:35 UT on 6 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251006A (trigger 781450060.028394 / 251006561). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 269.1, Dec = -16.6 (J2000 degrees, equivalent to J2000 17h 56m, -16d 36'), with a statistical uncertainty of 12.0 degrees. The angle from the Fermi LAT boresight is 30.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006561/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006561/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006561/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42124. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40191] GRB 251005C: SVOM/VT optical candidate
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42123 SUBJECT: GRB 251005C: SVOM/VT optical candidate DATE: 25/10/06 13:35:16 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> J. T. Palmerio (CEA), L. P. Xin, H. L. Li, Y. N. Ma, Z. H. Yao, Y. L. Qiu, C. Wu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC) report on behalf of the SVOM/VT team: SVOM/VT performed a Target of Opportunity observation of GRB 251005C detected by Swift (Page et al., GCN 42113) and Fermi GBM (Smith et al., GCN 42118), starting at 2025-10-06T02:00:33 UTC, 9.90 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued optical counterpart, compared to the PanSTARRS catalogue, is detected in VT_R at R.A., Dec. = 75.68455, 16.88019 degrees, equivalent to: R.A. (J2000) = 05h02m44.3s Dec. (J2000) = +16d52m48.7s with an uncertainty of 0.5 arcsec. This location is 4.6 arcsec from the Swift-XRT position (Goad et al. GCN 42116), outside of the 90% confidence region of 2.3 arcsec. The candidate's magnitudes are given below: Mid_time | Band | Exposure Time | Magnitude (AB) 11.18 hour VT_R 36*50 sec 22.64+/-0.25 mag 12.79 hour VT_R 36*50 sec 22.81+/-0.25 mag 10.71 hour VT_B 60*50 sec >23.7 mag 12.86 hour VT_B 50*50 sec >23.6 mag The fading of this candidate cannot be confirmed given the uncertainties. Our photometry is 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 Centre 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/42123. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40190] GRB 251005C: AstroSat CZTI detection
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42122 SUBJECT: GRB 251005C: AstroSat CZTI detection DATE: 25/10/06 13:31:57 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), U. Pathak (IITB), A. Goyal (IITB), Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), S. Salunke (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 GRB251005C which was also detected by Fermi/GBM (GCN Circ. 42118), Swift BAT (GCN Circ. 42113). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-10-05 16:06:52.04 UTC. The measured peak count rate associated with the burst is 218 (+69, -55) counts/s above the background in the combined data of all quadrants, with a total of 801 (+399, -369) counts. The local mean background count rate was 1373 (+5, -9) counts/s. Using cumulative rates, we measure a T90 of 9.6 (+5.3, -5.8) s. The source was also faintly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-10-05 16:06:54.50 UTC. The measured peak count rate associated with the burst is 90 (+28, -31) counts/s above the background in the combined data of three quadrants (out of four), with a total of 133 (+86, -91) counts. The local mean background count rate was 225 (+3, -3) counts/s. Due to poor statistics, we cannot reliably estimate the T90 from it. 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/42122. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40189] GRB 251005C: Swift/UVOT Upper Limits
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42121 SUBJECT: GRB 251005C: Swift/UVOT Upper Limits DATE: 25/10/06 10:20:47 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> N. P. M. Kuin (MSSL/UCL) and K. L. Page (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251005C 123 s after the BAT trigger (Page et al., GCN Circ. 42113). No optical afterglow consistent with the XRT position is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 123 273 147 >21.6 u_FC 336 586 246 >19.9 white 123 1536 392 >21.3 v 666 1586 117 >19.4 b 592 1676 108 >19.8 u 336 1659 343 >20.0 w1 715 1461 78 >19.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.461 in the direction of the burst (Schlegel et al. 1998). Please note that the initial GCN (Page et al., GCN Circ. 42113) reported 251005A "A-burst", which was corrected to "C" : GRB 251005C. View this GCN Circular online at https://gcn.nasa.gov/circulars/42121. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40188] GRB 250902A: MSU cubesats detection
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42120 SUBJECT: GRB 250902A: MSU cubesats detection DATE: 25/10/06 08:17:18 GMT FROM: Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> A. Bogomolov, V. Bogomolov, A. Iyudin, S. Svertilov, N. Vasiliev on behalf of the MSU “Sozvezdie-270” team, report: At 2025-09-02 ~01:30:00 UT the long-duration GRB 250320B (Fermi GBM detection: GCN #41648; SVOM detection: GCN #41653, GECAM-B detection: GCN #41687, VZLUSAT-2 detection: GCN #41701, CALET detection: GCN #41703) was detected on the cubesats Avion (the instruments DeCoR-1 and DeCoR-3) and Altair (DeCoR-2) of the Moscow University project “Sozvezdie-270” [1]. Total amount of photons detected by Avion is 644 (DeCoR-1, energy band 40-500 keV) and 583 (DeCoR-3, energy band 30-500 keV), it corresponds to a fluence of ~5*10^(-6) erg/cm^2 in the range 30-500 keV (DeCoR-3) and ~3*10^(-6) erg/cm^2 in the range 40-500 keV (DeCoR-1) LC in the energy range of 30-500 keV consists of a single episode of 7 s duration with a maximum flux of ~15 phot/(cm^2*s), supplemented at the beginning by an additional short increase (less than 2 s). А total duration (T90) of the burst is ~7 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/avion_d3_250902.png Parameters of GRB 250902A as well as other GRBs detected by Moscow University cubesats are listed at: https://swx.sinp.msu.ru/models/grb_cat/grb.php?lang=en Avion and Altair are the cubesats of the Moscow University project “Constellation-270” [1] launched on 2023 June 27 (Avion) and on 2024 November 5 (Altair). The payload of both cubesats is a set of scintillation gamma-ray detectors DeCoR [2], the energy range is >30 keV (Avion) and >50 keV (Altair), the time resolution is 0.5s (Avion) and 1 s (Altair). [1] Svertilov et al. 2023 https://link.springer.com/chapter/10.1007/978-3-031-50248-4_21 [2] Bogomolov et al. 2022 Universe 8, 282 https://www.mdpi.com/2218-1997/8/5/282 View this GCN Circular online at https://gcn.nasa.gov/circulars/42120. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40187] GRB 251005C: Swift-XRT refined Analysis
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42119 SUBJECT: GRB 251005C: Swift-XRT refined Analysis DATE: 25/10/06 04:38:56 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR), S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 7.6 ks of XRT data for GRB 251005C, from 129 s to 29.0 ks after the trigger. The data are entirely in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=1.34 (+/-0.06). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.41 (+0.27, -0.25). The best-fitting absorption column is 7.1 (+2.8, -2.2) x 10^21 cm^-2, in excess of the Galactic value of 3.2 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.4 x 10^-11 (8.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 7.1 (+2.8, -2.2) x 10^21 cm^-2 Galactic foreground: 3.2 x 10^21 cm^-2 Excess significance: 2.9 sigma Photon index: 1.41 (+0.27, -0.25) If the light curve continues to decay with a power-law decay index of 1.34, the count rate at T+24 hours will be 4.2 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.7 x 10^-14 (3.5 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01401726. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42119. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40186] GRB 251005C: Fermi GBM Observation
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42118 SUBJECT: GRB 251005C: Fermi GBM Observation DATE: 25/10/06 03:46:34 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> Jacob Smith (UAH), B. Mailyan (Florida Tech) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 16:06:54.00 UT on 05 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251005C (trigger 781373219/251005671), which was also detected by Swift BAT (K. L. Page et al. 2025, GCN 42113). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 98 degrees. The GBM light curve consists of a double emission episode with a duration (T90) of about 6 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+5.248 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.9 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 2136 +/- 866 keV. The event fluence (10-1000 keV) in this time interval is (3.2 +/- 0.2)E-06 erg/cm^2. The 64-millisec peak photon flux measured starting from T0+0.58 s in the 10-1000 keV band is 6.1 +/- 1.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/42118. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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