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[vsnet-grb-info 40240] GRB 251003A: Fermi GBM Observation
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42170 SUBJECT: GRB 251003A: Fermi GBM Observation DATE: 25/10/08 18:10:09 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 01:58:31.96 UT on 03 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251003A (trigger 781149516/251003082), which was also detected by Swift BAT (A. P. Beardmore et al. 2025, GCN 42070). The Fermi GBM on-ground location is consistent with the Swift BAT position. GTC/OSIRIS+ detected a spectroscopic redshift z = 4.412 (R. Sanchez-Ramirez et al. 2025, GCN 42086). The angle from the Fermi LAT boresight is 56 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 10 s (50-300 keV). The time-averaged spectrum from T0-4.1 to T0+6.1 s is best fit by a simple power law function with index -1.7 +/- 0.1. A Comptonized function fits equally well with a Epeak of 118 +/- 35 and alpha of -1.3 +/- 0.2. The event fluence (10-1000 keV) in this time interval is (1.1 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-1.5 s in the 10-1000 keV band is 1.6 +/- 0.2 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/42170. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40239] GRB 251003A: Fermi GBM Observation
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42170 SUBJECT: GRB 251003A: Fermi GBM Observation DATE: 25/10/08 18:10:09 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 01:58:31.96 UT on 03 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251003A (trigger 781149516/251003082), which was also detected by Swift BAT (A. P. Beardmore et al. 2025, GCN 42070). The Fermi GBM on-ground location is consistent with the Swift BAT position. GTC/OSIRIS+ detected a spectroscopic redshift z = 4.412 (R. Sanchez-Ramirez et al. 2025, GCN 42086). The angle from the Fermi LAT boresight is 56 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 10 s (50-300 keV). The time-averaged spectrum from T0-4.1 to T0+6.1 s is best fit by a simple power law function with index -1.7 +/- 0.1. A Comptonized function fits equally well with a Epeak of 118 +/- 35 and alpha of -1.3 +/- 0.2. The event fluence (10-1000 keV) in this time interval is (1.1 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-1.5 s in the 10-1000 keV band is 1.6 +/- 0.2 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/42170. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40238] GRB 251006B: Fermi GBM Observation
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42169 SUBJECT: GRB 251006B: Fermi GBM Observation DATE: 25/10/08 18:01:32 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 20:05:04.04 UT on 06 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251006B (trigger 781473909/251006837), which was also detected by Einstein Probe (Yin et al. 2025, GCN 42137) and SVOM/GRM (Wang et al. 2025, GCN 42139). The Fermi GBM on-ground location is consistent with the EP position. The angle from the Fermi LAT boresight is 104 degrees. The GBM light curve consists of one bright emission with a weaker secondary peak with total duration (T90) of about 5.9 s (50-300 keV). The time-averaged spectrum from T0-2.0 to T0+7.2 s is best fit by a Band function with Epeak = 330 +/- 14 keV, alpha = -0.61 +/- 0.03, and beta = -2.4 +/- 0.1. The event fluence (10-1000 keV) in this time interval is (2.06 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.38 s in the 10-1000 keV band is 26.2 +/- 0.4 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/42169. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40237] GRB 251007B: COLIBRÍ optical upper limit
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42168 SUBJECT: GRB 251007B: COLIBRÍ optical upper limit DATE: 25/10/08 15:32:24 GMT FROM: Francesco at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work(a)gmail.com> Francesco Magnani (CPPM), Camila Angulo (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), , Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the Swift/SVOM GRB 251007B (Melandri et al., GCN Circ. 42147, Webb et al., GCN Circ. 42148) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-08 10:34 to 12:32 UTC (from 14.9 to 16.8 hours after the trigger) and obtained 80 minutes of simultaneous exposure in the i and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and the tenue software, and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect a source at the SVOM/VT source position (Li et al., GCN Circ. 42163) down to the following 3-sigma limits: i > 23.3 z > 22.7 These upper limits are consistent with the ones reported by Wu et al. (GCN Circ. 42150). Our image is not deep enough to confirm fading of the source reported by Li et al. (GCN Circ. 42163). We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/42168. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40236] GRB 251007A: AstroSat CZTI detection
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42167 SUBJECT: GRB 251007A: AstroSat CZTI detection DATE: 25/10/08 12:42:43 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), A. Arya (IITB), A. Goyal (IITB), U. Pathak (IITB), 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-duration GRB 251007A which was also detected by Swift/BAT (GCN Circ. 42146), Glowbug (GCN Circ. 42151) and Calet GBM (GCN Circ. 42156). 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 2025-10-07 19:37:51.50 UTC. The measured peak count rate associated with the burst is 579 (+44, -41) counts/s above the background in the combined data three quadrants out of four, with a total of 4746 (+253, -236) counts. The local mean background count rate was 186 (+1, -2) counts/s. Using cumulative rates, we measure a T90 of 17.5 (+4.1, -1.3) 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 2025-10-07 19:37:49.6 UTC. The measured peak count rate associated with the burst is 1557 (+83, -88) counts/s above the background in the combined data of all quadrants, with a total of 9759 (+524, -526) counts. The local mean background count rate was 1146 (+3, -4) counts/s. We measure a T90 of 16.9 (+6.6, -1.3) 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/42167. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40235] GRB 251006B/EP251006a: EP-FXT afterglow detection
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42166 SUBJECT: GRB 251006B/EP251006a: EP-FXT afterglow detection DATE: 25/10/08 11:48:28 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. I. Yin (HKU), M. H. Zhang, T. Y. Liu, H. Y. Ren and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a second follow-up observation of GRB 251006B/EP251006a (GCN 42131, GCN 42137, GCN 42139, GCN 42155) at 2025-10-07T18:08:41 (UTC), about 22 hours after the WXT detection, with an exposure time of 4.9 ks. The source was also followed by several optical telescopes (GCN 42133, GCN 42138, GCN 42141). Two uncatalogued sources were detected within the WXT error circle (GCN 42140), of which Source 2 has faded with an unabsorbed flux of 3.37 x 10^-13 erg/s/cm^2 (22 hours) from the first observation at about 3.52 x 10^-12 erg/s/cm^2 (11 hours) in 0.5-10 keV. The position of Source 2 is R.A. = 40.5195 deg, DEC = -6.0346 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic), which is consistent with the SVOM/VT optical candidate (GCN 42141), and is therefore likely the GRB afterglow. 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/42166. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40234] GRB 250917B: iTelescope T-26 upper limit
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42165 SUBJECT: GRB 250917B: iTelescope T-26 upper limit DATE: 25/10/08 08:44:39 GMT FROM: Takanori Sakamoto at AGU <tsakamoto(a)phys.aoyama.ac.jp> H. Ban, T. Katou, Y. Nagata, K. Hotta, Y. Kawakubo, M. Serino, T. Sakamoto (AGU) We observed the field of GRB 250917B detected by Swift (Caputo et al., GCN Circ. 41848) and Fermi (Sonawane et al., GCN Circ. 41852) with the iTelescope.Net (http://www.itelescope.net) T26 (Planewave Delta Rho 500) telescope located at Utah Desert Remote Observatory (UT, USA). We took 20 images of 60 sec exposures in the Red filter starting from September 17 at 06:40:31 (UT), about 13 minutes after the Swift/BAT trigger and stopped at 07:10:25 (UT). We do not detect the optical afterglow in the individual images and the stacked image at the BAT refined position (Parsotan et al., GCN Circ. 41868). The estimated five sigma upper limits of the combined image (total exposure of 1200 sec) is 17.8 using the USNO-B1 catalog. View this GCN Circular online at https://gcn.nasa.gov/circulars/42165. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40233] EP250911a: Koshka Zeiss-1000 Optical Upper Limit
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42164 SUBJECT: EP250911a: Koshka Zeiss-1000 Optical Upper Limit DATE: 25/10/08 08:38:27 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), A. Novichonok (Petrozavodsk State University, KIAM), I. Nikolenko (INASAN), N. Pankov (HSE, IKI), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We observed the localization region of the Fast X-ray Transient EP250911a (Liang et al., GCN 41788; Liang et al., GCN 41809) using the 1-meter Zeiss-1000 telescope of the Simeiz (Koshka) Observatory with the R-band. Observations were performed on Sep. 13, 14, and 16 in the presence of the full Moon. In the stacked frame of the three epochs we did not detect the optical afterglow (Quirola-Vasquez et al., GCN 41790; Angulo et al., GCN 41793; Lai et al., GCN 41801; Evans et al., GCN 41802; Moskvitin & Spiridonova, GCN 41805; Ma et al., GCN 41807). The photometry based on nearby PS1 stars (Lupton's transformation) is the following: Date UT start t-T0 Exp. Filter OT Err. UL (mid, days) (n*s) (3sigma) 2025-09-13 22:44:37 2.60543 45*120 R n/d n/d 21.0 2025-09-14 19:41:15 3.52607 60*120 R n/d n/d 21.7 2025-09-16 20:58:57 5.54397 60*120 R n/d n/d 21.9 2025-09-13+14+16 22:44:37 4.08066 165*120 R n/d n/d 22.6 View this GCN Circular online at https://gcn.nasa.gov/circulars/42164. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40232] GRB 251007B: SVOM/VT optical candidate
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42163 SUBJECT: GRB 251007B: SVOM/VT optical candidate DATE: 25/10/08 08:36:55 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, 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), J. Palmerio (CEA), N. A. Webb, O. Godet report on behalf of the SVOM/VT Instrument Center: SVOM/VT conducted ToO follow-up observations of GRB 251007B (sb25100703) (Melandri et al., GCN 42147; Webb et al., GCN 42148). The observation started on 2025-10-07T21:41:47 UT, 1.98 hours after the burst, in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. Within the error box of enhanced XRT position (Osborne et al., GCN 42159), an uncatalogued source was detected in both channels of VT, compared to the PanSTARRS catalogue. The position is at R.A., Dec. = 102.1329813, -10.3040289 degrees, equivalent to: R.A. (J2000) = 6:48:31.92 Dec. (J2000) = -10:18:14.50 with an uncertainty of 0.5 arcsec. The magnitudes are as follows: Mid_time | Band | Exposure Time | Magnitude (AB) 4.82 hour VT_R 43*70 sec 23.00+/-0.20 mag 4.82 hour VT_B 43*70 sec 23.53+/-0.24 mag Our photometry is 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/42163. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40231] GRB 251007A: Swift-XRT refined Analysis
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42162 SUBJECT: GRB 251007A: Swift-XRT refined Analysis DATE: 25/10/08 08:34:11 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.5 ks of XRT data for GRB 251007A, from 58 s to 39.2 ks after the trigger. The data comprise 362 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+11.9 ks) can be modelled with a power-law decay with a decay index of alpha=1.46 (+/-0.13). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.92 (+/-0.04). The best-fitting absorption column is 1.79 (+0.15, -0.14) x 10^21 cm^-2, in excess of the Galactic value of 4.0 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.82 (+/-0.12) and a best-fitting absorption column of 1.6 (+/-0.4) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.9 x 10^-11 (4.9 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.6 (+/-0.4) x 10^21 cm^-2 Galactic foreground: 4.0 x 10^20 cm^-2 Excess significance: 5.1 sigma Photon index: 1.82 (+/-0.12) If the light curve continues to decay with a power-law decay index of 1.46, the count rate at T+24 hours will be 0.052 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.0 x 10^-12 (2.5 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01402466. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42162. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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