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

[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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[vsnet-grb-info 40230] GRB 251007A: Enhanced Swift-XRT position
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42161 SUBJECT: GRB 251007A: Enhanced Swift-XRT position DATE: 25/10/08 08:06:25 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 1898 s of XRT Photon Counting mode data and 7 UVOT images for GRB 251007A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 128.17650, +21.81297 which is equivalent to: RA (J2000): 08h 32m 42.36s Dec (J2000): +21d 48' 46.7" with an uncertainty of 2.0 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42161. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40229] GRB 251007B: Swift-XRT refined Analysis
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42160 SUBJECT: GRB 251007B: Swift-XRT refined Analysis DATE: 25/10/08 07:17:36 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore (U. Leicester), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), J.P. Osborne (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.4 ks of XRT data for GRB 251007B, from 134 s to 33.2 ks after the trigger. The data comprise 6 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=1.68 (+0.24, -0.26). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.79 (+0.39, -0.25). The best-fitting absorption column is 6.5 (+3.1, -0.5) x 10^21 cm^-2, consistent with the Galactic value of 6.0 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 5.0 x 10^-11 (7.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 6.5 (+3.1, -0.5) x 10^21 cm^-2 Galactic foreground: 6.0 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.79 (+0.39, -0.25) If the light curve continues to decay with a power-law decay index of 1.68, the count rate at T+24 hours will be 3.9 x 10^-5 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.9 x 10^-15 (2.9 x 10^-15) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01402467. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42160. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40228] GRB 251007B: Enhanced Swift-XRT position
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42159 SUBJECT: GRB 251007B: Enhanced Swift-XRT position DATE: 25/10/08 07:13:08 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 1164 s of XRT Photon Counting mode data and 2 UVOT images for GRB 251007B, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 102.13270, -10.30374 which is equivalent to: RA (J2000): 06h 48m 31.85s Dec (J2000): -10d 18' 13.4" with an uncertainty of 2.5 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42159. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40227] GRB 251007A: NOT optical observations
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42158 SUBJECT: GRB 251007A: NOT optical observations DATE: 25/10/08 06:46:01 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), T. Pursimo (NOT), A. L. Bouquin (NOT and DTU Space) report on behalf of a larger collaboration: We observed the optical afterglow of GRB 251007A (Ambrosi et al., GCN 42146; Wu et al., GCN 42154) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started on 2025 Oct 8.16 UT (8.2 hr after the trigger), as soon as the target was visible from La Palma, and consisted of images in the SDSS g, r, and i filters. In a stack of nine 200 s images, we measure i = 21.07 +- 0.07 at a mean epoch of 2025 Oct 8.17 UT (8.46 hr after the trigger). This magnitude is in the AB system, is calibrated against nearby stars from the Pan-STARRS catalog, and is not corrected for Galactic extinction. The afterglow looks red, with a color r-i ~ 0.4, which corresponds to a spectral slope alpha ~ 1.9 (F_nu propto nu^-alpha). This is consistent with the bright i-band detection by SVOM/C-GFT (Wu et al., GCN 42154). View this GCN Circular online at https://gcn.nasa.gov/circulars/42158. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40226] GRB 251007A: AKO Optical Upper Limit
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42157 SUBJECT: GRB 251007A: AKO Optical Upper Limit DATE: 25/10/08 05:50:58 GMT FROM: Mohammad Odeh at Al Khatim Observatory M44 <mshodeh(a)gmail.com> Mohammad Odeh (Al-Khatim Observatory - AKO, operated by the International Astronomical Center in Abu Dhabi, UAE), Nidhal Guessoum (American University of Sharjah, UAE), and Shaikha Alshamsi (University of Sharjah, UAE), report: We observed the field of GRB 251007A detected by Swift/BAT (Ambrosi et al., GCN 42146) and Glowbug (Cheung et al., GCN 42151), using our 0.36m f/7.7 robotic telescope. The observation session began on 07 October 2025 at 23:03 UT, with a midpoint at 23:45 UT, approximately 4.1 hours after the trigger. We did not detect any uncatalogued source down to Ic=17.8 (5-sigma), not corrected for galactic extinction, at the position reported by Swift/UVOT (Ambrosi et al., GCN 42146). View this GCN Circular online at https://gcn.nasa.gov/circulars/42157. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40225] GRB 251007A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42156 SUBJECT: GRB 251007A: CALET Gamma-Ray Burst Monitor detection DATE: 25/10/08 05:38:59 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 251007A (Swift detection: Ambrosi et al., GCN Circ. 42146; Glowbug gamma-ray detection: Cheung et al., GCN Circ. 42151) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 19:37:48.18 UTC on 7 October 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1443900615/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure that starts at T+3.0 sec, peaks at T+6.3 sec, and ends at T+21.9 sec. The T90 and T50 durations measured by the SGM data are 15.7 +/- 0.3 sec and 9.2 +/- 0.3 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1443900615/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/42156. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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