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[vsnet-grb-info 40257] GRB 251009B: Insight-HXMT detection of a short burst
by GCN Circulars 10 Oct '25

10 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42187 SUBJECT: GRB 251009B: Insight-HXMT detection of a short burst DATE: 25/10/10 15:50:38 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-10-09T01:51:15.250 (T0), Insight-HXMT/HE detected the burst GRB 251009B, which is also detected by SVOM/GRM. The Insight-HXMT/HE light curve mainly consists of double pulses with a T90 of 1.00 +0.15/-0.05 s. The total counts from this burst is 2442 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251009B.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/42187. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40256] GRB 251007A: Swift-BAT refined analysis
by GCN Circulars 10 Oct '25

10 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42186 SUBJECT: GRB 251007A: Swift-BAT refined analysis DATE: 25/10/10 14:08:25 GMT FROM: Takanori Sakamoto at AGU <tsakamoto(a)phys.aoyama.ac.jp> S. Laha (GSFC/UMBC), E. Ambrosi (INAF-IASFPA), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+303 sec from the recent telemetry downlink, we report further analysis of BAT GRB 251007A (trigger #1402466) (Ambrosi, et al., GCN Circ. 42146). The BAT ground-calculated position is RA, Dec = 128.162, 21.810 deg which is RA(J2000) = 08h 32m 38.8s Dec(J2000) = +21d 48' 36.6" with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 85%. The mask-weighted light curve shows a complex structure starting at ~T-1 sec, peaking at T+56 sec, and decaying to background at T+110 sec. T90 (15-350 keV) is 64.19 +- 5.17 sec (estimated error including systematics). The time-averaged spectrum from T-0.04 to T+103.43 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.32 +- 0.03. The fluence in the 15-150 keV band is 1.04 +- 0.02 x 10^-5 erg/cm2. The 1-sec peak photon flux measured from T+56.14 sec in the 15-150 keV band is 9.5 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1402466 View this GCN Circular online at https://gcn.nasa.gov/circulars/42186. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40255] GRB 251009A: SVOM/GRM observation of short GRB with possible tail emission
by GCN Circulars 10 Oct '25

10 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42185 SUBJECT: GRB 251009A: SVOM/GRM observation of short GRB with possible tail emission DATE: 25/10/10 13:32:03 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shu-Xu Yi, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Piron (LUPM) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a short burst GRB 251009A (SVOM trigger reference: sb25100902) at 2025-10-09T15:58:56.500 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#42179). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a narrow spike followed by a weak tail emission with a T90 of 0.32 +0.05/-0.11 s in the 15-5000 keV band, which is somewhat similar to extragalactic magnetar giant flare. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251009A.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/42185. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40254] GRB 251007A: SVOM/GRM observation
by GCN Circulars 10 Oct '25

10 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42184 SUBJECT: GRB 251007A: SVOM/GRM observation DATE: 25/10/10 12:47:58 GMT FROM: yzh807926(a)163.com SVOM/GRM team: Zheng-Hang Yu, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Feliu Lacreu (IAP), Sebastien Guillot (IRAP), Olivier GODET (IRAP), Marius Brunet (IRAP), Frédéric Piron (LUPM), Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 251007A (SVOM trigger reference: sb25100703) at 2025-10-07T19:37:53.000 UTC (T0), which is also detected by Swift/BAT (Ambrosi et al. 2025, GCN #42146), Glowbug (Cheung et al. 2025, GCN #42151) and CALET/GBM (A. Yoshida et al. 2025, GCN #42156). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a precursor followed by a main episode with multiple peaks a T90 of 58.0 +1.5/-5.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251007A.png In addition, the position of this burst, as determined by Swift/BAT (RA= 128.1775, DEC= 21.8138, GCN#42146), is located at about 49 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. Nevertheless, ECLAIRs detected the burst above 50 keV through its shield. With this localization, the time-averaged spectrum from T0-50 to T0+30 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.27 +0.04/-0.04 and the cutoff energy, parameterized as Epeak, is 761 +219/-152 keV. The event fluence (10-1000 keV) in this time interval is (3.97 +0.14/-0.15)E-05 erg/cm^2. The localization of GRB 251007A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251007A_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: Zheng-Hang Yu(IHEP)(zhyu(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42184. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40253] GRB 251007A: Insight-HXMT detection
by GCN Circulars 10 Oct '25

10 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42183 SUBJECT: GRB 251007A: Insight-HXMT detection DATE: 25/10/10 12:33:04 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Zheng-Hang Yu, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-10-07T19:37:51.750 (T0), Insight-HXMT/HE detected the burst GRB 251007A, which is also detected by Swift/BAT (E. Ambrosi et al, GCN#42146), Glowbug (C.C. Cheun et al., GCN#42151), CALET/GBM (A. Yoshida et al., GCN#42156) and AstroSat (S. Salunke et al., GCN#42167). The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 57.4 +1.8/-16.2 s. The 1s peak rate, measured from T0+0.7 s, is 7246 cnts/sec. The total counts from this burst is 52938 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251007A.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/42183. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40252] GRB 251006A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 10 Oct '25

10 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42182 SUBJECT: GRB 251006A: CALET Gamma-Ray Burst Monitor detection DATE: 25/10/10 10:17:47 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> T. Sakamoto, A. Yoshida, 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 short GRB 251006A (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 42124; Glowbug gamma-ray detection: Cheung et al., GCN Circ. 42130; Swift/BAT-GUANO subthreshold detection: DeLaunay et al., GCN Circ. 42144; Fermi GBM Observation: Palafox et al., GCN Circ. 42175) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 13:27:35.21 UTC on 6 October 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1443792004/index.html) The burst signal was seen by only the SGM detector. No real-time CGBM GCN notice was distributed about this trigger because the real-time communication from the ISS was off (loss of signal). The burst light curve shows a single pulse that starts at T-0.22 sec and ends at T+0.04 sec. The T90 and T50 durations measured by the SGM data are 0.21 +/- 0.05 sec and 0.11 +/- 0.05 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1443792004/ 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/42182. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40251] GRB 251007B - SVOM/ECLAIRs refined analysis
by GCN Circulars 10 Oct '25

10 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42181 SUBJECT: GRB 251007B - SVOM/ECLAIRs refined analysis DATE: 25/10/10 08:31:06 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Authors: O. Godet, S. Guillot (IRAP), F. Lacreu (IAP), M. Brunet, N. A. Webb (IRAP) Using the event-by-event data downloaded through the X-band ground stations, we report further analysis of ECLAIRs observations of GRB 251007B (SVOM burst-id sb25100703). The burst that triggered ECLAIRs onboard (Webb et al., GCN Circ. #42148) consists of a simple peak structure with a duration of T90 = 33.16 -6.76 / +3.58 s in the 4-120 keV energy band. The time-averaged spectrum from T0-18 s to T0+22 s (T0 = 2025-10-07T19:43:23) in the energy range 5-70 keV is best fitted by a powerlaw model with a photon index of 1.58 +0.15/-0.14. With this model, the total 4-120 keV fluence is (9.0 +0.4/-0.2)e-7 erg/cm^2. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: O. Godet (IRAP) (ogodet at irap.omp.eu) View this GCN Circular online at https://gcn.nasa.gov/circulars/42181. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40250] SVOM/sb25101004: SVOM detection of a stellar flare
by GCN Circulars 10 Oct '25

10 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42180 SUBJECT: SVOM/sb25101004: SVOM detection of a stellar flare DATE: 25/10/10 07:23:03 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Donghua ZHAO, Chao Wu, Wenjin Xie (NAOC), Hatsunegoto Goto(Kanazawa Univ./CEA)，Florent Robinet (IJCLab), Nicolas Dagoneau, J. T. Palmerio (CEA) report on behalf of the SVOM mission team At 2025-10-10T03:51:58 UTC (T0), SVOM/ECLAIRs triggered and located the source (SVOM burst-id sb25101004). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The source was only detected by the Image Trigger (IMT), which produced a sequence of 5 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.82 in the [5-20] keV energy band over a time window of 327.68 seconds starting at 2025-10-10T03:47:53. The localization of the best alert is R.A., Dec.: 311.3214, -31.4119 degrees (J2000) with a 90% confidence level (C.L.) radius of 8.10 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the source. SVOM/MXT began observing the field at 2025-10-10T04:00:23 UTC, 505 seconds after T0. Using X band data we found a source located at R.A., Dec.: 311.2972, -31.3445 degrees: R.A. (J2000) = 20h45m11.338s Dec. (J2000) = -31d20m40.213s with a 90% C.L. radius of 25.8 arcseconds (including a systematic error of 25 arcsec added in quadrature). This location is 4.23 arcminutes from the ECLAIRs onboard position. No uncatalogued fading X-ray counterpart was detected. There is a known source HD 197481 (Au Mic: a young red dwarf star ) which is 4.23 arcmin away from ECLAIRs position and is 26 arcsec away from MXT position. These results show that this trigger is probably caused by the stellar flare of HD 197481 (Au Mic). The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Donghua Zhao: zhaodh(a)bao.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42180. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40249] GRB 251009A: Fermi GBM Final Localization
by GCN Circulars 10 Oct '25

10 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42179 SUBJECT: GRB 251009A: Fermi GBM Final Localization DATE: 25/10/10 00:04:26 GMT FROM: Matt Godwin <msg0028(a)uah.edu> The Fermi GBM team reports the detection of a likely SHORT GRB "At 15:58:56.61 UT on 09 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251009A (trigger 781718341/251009666). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 72.05, Dec = -25.84 (J2000 degrees, equivalent to J2000 4h 48m, -25d 50'), with a statistical uncertainty of 25.22 degrees. The angle from the Fermi LAT boresight is 86 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251009666/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251009666/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251009666/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/42179. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40248] GRB 250916A: TERI Gamma-ray detection
by GCN Circulars 09 Oct '25

09 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42178 SUBJECT: GRB 250916A: TERI Gamma-ray detection DATE: 25/10/09 21:13:22 GMT FROM: Daniel Shy <danielshy(a)danielshy.com> Daniel Shy (a), C.C. Cheung (a), Bernard Phlips (a), Michael Streicher (b), James Mason (b), Douglas M. Groves (b), Feng Zhang (b), Willy Kaye (b) (a) U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (b) H3D, Inc., 812 Avis Dr., Ann Arbor, MI 48108, USA The cadmium zinc TElluride Radiation Imager (TERI) gamma-ray telescope [1], operating on the International Space Station, reports the detection of GRB 250916A, which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ., 41839), Astrosat/CZTI (Arya et al., GCN Circ. 41843), Glowbug (Cheung et al., GCN Circ. 41855), CALET/GBM (Trig ID. 1442064382), and NuSTAR (41871). Using 1 Hz binning, the peak count rate is roughly 23 excess counts per second (cps) at ~T0+259s (adopting T0 = 2025-09-16 13:29:21.1) over a baseline rate of 41-cps observed in nearby off-source intervals. We do not detect the initial faint burst at T0 detected by Fermi/GBM. The analysis results presented here are preliminary and currently lack a detailed response function. TERI is an Office of Naval Research funded technology demonstrator for large-volume pixelated CdZnTe detectors developed, built, and operated by the U.S. Naval Research Laboratory (NRL) in conjunction with H3D, Inc. The pixelated CdZnTe detectors have an energy of 40 keV to 3 MeV per pixel. It was launched on 2025 April 21 aboard the Department of Defense Space Test Program’s STP-H10 to the ISS. On the ISS, it is located on the SOX external payload facility on the Columbus module. [1] Shy, Daniel, et al. "Development of the cadmium zinc TElluride Radiation Imager." Journal of Astronomical Telescopes, Instruments, and Systems 10.4 (2024): 044009-044009 (arXiv:2408.04559). Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42178. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40247] GRB 250919A: TERI gamma-ray detection
by GCN Circulars 09 Oct '25

09 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42177 SUBJECT: GRB 250919A: TERI gamma-ray detection DATE: 25/10/09 21:09:21 GMT FROM: Daniel Shy <danielshy(a)danielshy.com> Daniel Shy (a), C.C. Cheung (a), Bernard Phlips (a), Michael Streicher (b), James Mason (b), Douglas M. Groves (b), Feng Zhang (b), Willy Kaye (b) (a) U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375 (b) H3D, Inc., 812 Avis Dr., Ann Arbor, MI 48108, USA The cadmium zinc TElluride Radiation Imager (TERI) gamma-ray telescope [1], operating on the International Space Station, reports the detection of GRB 250919A, which was also detected by Fermi/GBM, SVOM/GRM, EP/WXT, NuSTAR, Glowbug, Insight-HXMT, and Konus-Wind (Fermi GBM team, GCN 41874; Wang et al., GCN 41882; Liang et al., GCN 41879; Waratkar & Grefenstette, GCN 41888; Cheung et al., GCN 41891, Wang et al., GCN 41900; Frederiks et al., GCN 41905) Using 1 Hz binning, and adopting T0 = 2025-09-19 00:28:52.28, we observe the three dominant peaks seen in the Fermi/GBM lightcurve (GCN 41874) at ~T0+24s, ~T0+26s, and ~T0+29s with respective peak excess count rates of roughly 57, 171, and 104 counts per second (cps) above the 27-cps baseline rate observed in nearby off-source intervals. We do not observe the fainter, leading feature at ~T0, as seen in the Fermi/GBM lightcurve. The analysis results presented here are preliminary and currently lack a detailed response function. TERI is an Office of Naval Research funded technology demonstrator for large-volume pixelated CdZnTe detectors developed, built, and operated by the U.S. Naval Research Laboratory (NRL) in conjunction with H3D, Inc. The pixelated CdZnTe detectors have an energy of 40 keV to 3 MeV per pixel. It was launched on 2025 April 21 aboard the Department of Defense Space Test Program’s STP-H10 to the ISS. On the ISS, it is located on the SOX external payload facility on the Columbus module. [1] Shy, Daniel, et al. "Development of the cadmium zinc TElluride Radiation Imager." Journal of Astronomical Telescopes, Instruments, and Systems 10.4 (2024): 044009-044009 (arXiv:2408.04559). Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42177. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40246] EP251006a: Global MASTER-Net observations report
by GCN Circulars 09 Oct '25

09 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42176 SUBJECT: EP251006a: Global MASTER-Net observations report DATE: 25/10/09 20:18:28 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP251006a ( EP Team et al., GCN 42137) errorbox 196 sec after trigger time at 2025-10-07 18:11:57 UT, with upper limit up to 16.6 mag. The observations began at zenith distance = 79 deg. The sun altitude is -37.7 deg. MASTER-SAAO robotic telescope located in South Africa (South African Astronomical Observatory) was pointed to the EP251006a errorbox 3541 sec after trigger time at 2025-10-07 19:07:42 UT, with upper limit up to 18.5 mag. The observations began at zenith distance = 75 deg. The sun altitude is -29.6 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP251006a errorbox 40526 sec after trigger time at 2025-10-08 05:24:07 UT, with upper limit up to 18.7 mag. The observations began at zenith distance = 27 deg. The sun altitude is -50.3 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=3010044 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 226 | 2025-10-07 18:11:57 | MASTER-Kislovodsk | (02h 39m 56.00s , -06d 09m 59.8s) | C | 60 | 14.6 | 226 | 2025-10-07 18:11:57 | MASTER-Kislovodsk | (02h 39m 54.59s , -05d 47m 17.6s) | C | 60 | 15.4 | 508 | 2025-10-07 18:16:38 | MASTER-Kislovodsk | (02h 39m 49.79s , -05d 48m 02.3s) | C | 60 | 15.5 | 508 | 2025-10-07 18:16:38 | MASTER-Kislovodsk | (02h 39m 51.52s , -06d 10m 40.5s) | C | 60 | 14.6 | 823 | 2025-10-07 18:21:54 | MASTER-Kislovodsk | (02h 39m 48.84s , -05d 45m 43.0s) | C | 60 | 15.5 | 883 | 2025-10-07 18:21:54 | MASTER-Kislovodsk | (02h 39m 48.82s , -05d 45m 42.9s) | C | 180 | 16.2 | Coadd 823 | 2025-10-07 18:21:54 | MASTER-Kislovodsk | (02h 39m 51.15s , -06d 08m 22.6s) | C | 60 | 14.9 | 903 | 2025-10-07 18:23:14 | MASTER-Kislovodsk | (02h 39m 51.14s , -06d 10m 23.8s) | C | 60 | 14.9 | 903 | 2025-10-07 18:23:14 | MASTER-Kislovodsk | (02h 39m 48.76s , -05d 47m 43.3s) | C | 60 | 15.5 | 1250 | 2025-10-07 18:29:00 | MASTER-Kislovodsk | (02h 39m 55.32s , -05d 47m 15.7s) | C | 60 | 15.6 | 1250 | 2025-10-07 18:29:00 | MASTER-Kislovodsk | (02h 39m 57.09s , -06d 10m 09.1s) | C | 60 | 14.6 | 3572 | 2025-10-07 19:07:42 | MASTER-SAAO | (02h 38m 20.93s , -06d 05m 34.6s) | C | 60 | 17.0 | 3572 | 2025-10-07 19:07:42 | MASTER-SAAO | (02h 40m 07.46s , -06d 21m 24.6s) | C | 60 | 13.5 | 40556 | 2025-10-08 05:24:07 | MASTER-OAFA | (02h 38m 04.24s , -06d 11m 37.8s) | C | 60 | 18.6 | 40631 | 2025-10-08 05:25:22 | MASTER-OAFA | (02h 38m 03.16s , -06d 10m 39.1s) | C | 60 | 18.6 | 40868 | 2025-10-08 05:29:18 | MASTER-OAFA | (02h 38m 02.78s , -06d 12m 42.4s) | C | 60 | 18.7 | 40945 | 2025-10-08 05:30:36 | MASTER-OAFA | (02h 46m 13.59s , -06d 12m 15.1s) | C | 60 | 18.7 | 41021 | 2025-10-08 05:31:52 | MASTER-OAFA | (02h 46m 09.43s , -06d 10m 39.7s) | C | 60 | 18.6 | 41099 | 2025-10-08 05:33:10 | MASTER-OAFA | (02h 46m 09.23s , -06d 12m 05.1s) | C | 60 | 18.6 | 43486 | 2025-10-08 06:12:57 | MASTER-OAFA | (02h 46m 25.97s , -05d 55m 21.1s) | C | 60 | 18.7 | 43564 | 2025-10-08 06:14:15 | MASTER-OAFA | (02h 46m 30.99s , -05d 55m 10.3s) | C | 60 | 18.7 | 43638 | 2025-10-08 06:15:29 | MASTER-OAFA | (02h 46m 28.25s , -05d 53m 31.6s) | C | 60 | 18.7 | 86664 | 2025-10-08 18:12:34 | MASTER-Kislovodsk | (02h 39m 48.87s , -05d 45m 56.5s) | C | 60 | 15.5 | 86724 | 2025-10-08 18:12:34 | MASTER-Kislovodsk | (02h 39m 48.87s , -05d 45m 56.4s) | C | 180 | 16.0 | Coadd 86664 | 2025-10-08 18:12:34 | MASTER-Kislovodsk | (02h 39m 49.14s , -06d 09m 00.5s) | C | 60 | 14.8 | 86744 | 2025-10-08 18:13:54 | MASTER-Kislovodsk | (02h 39m 58.79s , -05d 49m 41.8s) | C | 60 | 15.4 | 86744 | 2025-10-08 18:13:54 | MASTER-Kislovodsk | (02h 39m 59.30s , -06d 12m 47.1s) | C | 60 | 14.1 | 87245 | 2025-10-08 18:22:15 | MASTER-Kislovodsk | (02h 39m 49.23s , -05d 46m 24.8s) | C | 60 | 15.4 | 87245 | 2025-10-08 18:22:15 | MASTER-Kislovodsk | (02h 39m 52.54s , -06d 09m 03.4s) | C | 60 | 15.4 | 88594 | 2025-10-08 18:44:45 | MASTER-Kislovodsk | (02h 39m 53.25s , -05d 46m 54.7s) | C | 60 | 15.8 | 88654 | 2025-10-08 18:44:45 | MASTER-Kislovodsk | (02h 39m 53.24s , -05d 46m 54.5s) | C | 180 | 16.6 | Coadd 88594 | 2025-10-08 18:44:45 | MASTER-Kislovodsk | (02h 39m 57.09s , -06d 10m 00.7s) | C | 60 | 16.3 | 88935 | 2025-10-08 18:50:26 | MASTER-Kislovodsk | (02h 39m 52.51s , -05d 45m 44.1s) | C | 60 | 16.0 | 88935 | 2025-10-08 18:50:26 | MASTER-Kislovodsk | (02h 39m 58.82s , -06d 08m 32.2s) | C | 60 | 16.4 | 89015 | 2025-10-08 18:51:46 | MASTER-Kislovodsk | (02h 39m 58.46s , -05d 46m 41.6s) | C | 60 | 16.0 | 89015 | 2025-10-08 18:51:46 | MASTER-Kislovodsk | (02h 40m 04.85s , -06d 09m 31.8s) | C | 60 | 16.3 | 89095 | 2025-10-08 18:53:06 | MASTER-Kislovodsk | (02h 39m 48.54s , -05d 44m 54.1s) | C | 60 | 15.9 | 89155 | 2025-10-08 18:53:06 | MASTER-Kislovodsk | (02h 39m 48.54s , -05d 44m 54.2s) | C | 180 | 16.6 | Coadd 89095 | 2025-10-08 18:53:06 | MASTER-Kislovodsk | (02h 39m 55.02s , -06d 07m 45.0s) | C | 60 | 16.4 | 89175 | 2025-10-08 18:54:25 | MASTER-Kislovodsk | (02h 39m 54.56s , -05d 46m 36.7s) | C | 60 | 16.0 | 89175 | 2025-10-08 18:54:25 | MASTER-Kislovodsk | (02h 40m 01.09s , -06d 09m 28.4s) | C | 60 | 16.2 | 89255 | 2025-10-08 18:55:46 | MASTER-Kislovodsk | (02h 39m 54.62s , -05d 44m 51.0s) | C | 60 | 16.1 | 89255 | 2025-10-08 18:55:46 | MASTER-Kislovodsk | (02h 40m 01.20s , -06d 07m 42.8s) | C | 60 | 16.4 | 89335 | 2025-10-08 18:57:06 | MASTER-Kislovodsk | (02h 40m 00.54s , -05d 48m 27.7s) | C | 60 | 15.9 | 89335 | 2025-10-08 18:57:06 | MASTER-Kislovodsk | (02h 40m 07.15s , -06d 11m 19.7s) | C | 60 | 16.3 | 89937 | 2025-10-08 19:07:07 | MASTER-Kislovodsk | (02h 39m 50.59s , -05d 42m 57.7s) | C | 60 | 16.1 | 89937 | 2025-10-08 19:07:07 | MASTER-Kislovodsk | (02h 39m 56.71s , -06d 06m 09.4s) | C | 60 | 16.4 | 90017 | 2025-10-08 19:08:27 | MASTER-Kislovodsk | (02h 39m 53.56s , -05d 47m 41.3s) | C | 60 | 16.0 | 90017 | 2025-10-08 19:08:27 | MASTER-Kislovodsk | (02h 39m 59.66s , -06d 10m 54.2s) | C | 60 | 16.4 | 111807 | 2025-10-09 01:11:38 | MASTER-SAAO | (02h 41m 40.45s , -06d 20m 51.9s) | C | 60 | 18.2 | 111807 | 2025-10-09 01:11:38 | MASTER-SAAO | (02h 39m 51.83s , -06d 05m 32.4s) | C | 60 | 18.5 | 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/42176. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40245] GRB 251006A: Fermi GBM Observation
by GCN Circulars 09 Oct '25

09 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42175 SUBJECT: GRB 251006A: Fermi GBM Observation DATE: 25/10/09 15:08:56 GMT FROM: Eva MP <eva.palafox(a)gmail.com> E. Palafox (INAOE), M. Godwin (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 13:27:35.03 UT on 06 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251006A (trigger 781450060/251006561), which was also detected by Swift/BAT-GUANO (J. DeLaunay et al. 2025, GCN 42144) and Glowbug (C. C. Cheung et al. 2025, GCN 42130). The Fermi GBM on-ground location is consistent with the Swift/BAT-GUANO position. The angle from the Fermi LAT boresight is 30 degrees. The GBM light curve consists of one short emission with total duration (T90) of about 1.4 s (50-300 keV). The time-averaged spectrum from T0-0.3 to T0+0.3 s is best fit by a Comptonized function with Epeak of 490 +/- 170 and alpha of -0.9 +/- 0.2. The event fluence (10-1000 keV) in this time interval is (4.8 +/- 0.6)E-07 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.0 s in the 10-1000 keV band is 7 +/- 1 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/42175. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40244] GRB 251007A: 1.5m OSN and 2.2m CAHA optical follow-up
by GCN Circulars 09 Oct '25

09 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42174 SUBJECT: GRB 251007A: 1.5m OSN and 2.2m CAHA optical follow-up DATE: 25/10/09 11:20:11 GMT FROM: Youdong HU at INAF-OAB <huyoudong072(a)hotmail.com> Y.-D. Hu (GXU), F. Aceituno, A. J. Castro-Tirado, E. Fernandez-Garcia, I. Perez-Garcia, S.-Y. Wu, M. D. Caballero-Garcia, R. Sanchez-Ramirez, and S. Guziy (IAA-CSIC) and A. Fernández-Martín (CAHA) on behalf of a larger collaboration, report: Following the detection of GRB 251007A by Swift (Ambrosi et al. GCNC 42146), we triggered the 1.5m OSN telescope in Granada (Spain) starting on Oct. 08 at 04:17:06 UT (~8.8 hrs post burst), a series of I-band image was gathered. In the stacked image, the optical afterglow is detected within the Swift/XRT error region (Beardmore et al. GCNC 42161) with I=21.21+-0.19. About 20 mins later, the 2.2m CAHA telescope (+ CAFOS) at the Calar Alto Observatory (Almeria, Spain) also triggered to start taking images with Sloan-griz filters. The optical afterglow is detected in the stacked image with i=22.0+-0.3. These detections are consistent with the reports from UVOT (Ambrosi et al. GCNC 42146), MASTER (Lipunov et al. GCNC 42149), SVOM/C-GFT (Wu et al. GCNC 42154), AKO (Odeh et al. GCNC 42157), NOT (Malesani et al. GCNC 42158) and SVOM/VT (Li et al. GCNC 42163). We thank the staff at OSN and Calar Alto observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/42174. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40243] GRB 251002A - SVOM/ECLAIRs refined analysis
by GCN Circulars 09 Oct '25

09 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42173 SUBJECT: GRB 251002A - SVOM/ECLAIRs refined analysis DATE: 25/10/09 06:55:38 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. G. Bernardini (INAF-OAB, LUPM), U. Jacob, F. Piron (LUPM), M. Brunet, O. Godet (IRAP), N. Dagoneau, B. Hubert, S. Schanne, A. Saccardi, D. Gotz (CEA/Irfu) Using the event-by-event data downloaded through the X-band ground stations, we report further analysis of ECLAIRs observations of GRB 251002A (SVOM burst-id sb25100211). The burst that triggered ECLAIRs onboard (Saccardi et al., GCN Circ. 42060) consists of a multiple peak structure with a duration of T90 = (8.2 -0.3/+1.82) s in the 4-120 keV energy band. After this main emission episode, the source is still visible through image deconvolution as a dim source up to about 30 s after T0 (T0 = 2025-10-02T20:14:54 s). The time-averaged spectrum from T0-3 s to T0+8 s in the energy range 5-120 keV is best fitted by a cutoff power law model with index (0.72 +0.18/-0.20) and E0 = (79 +68/-26) keV. With this model, the total 4-120 keV fluence is (2.57 +/-0.03)e-6 erg/cm^2. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: M. G. Bernardini (INAF-OAB, LUPM) (maria.bernardini at inaf.it) View this GCN Circular online at https://gcn.nasa.gov/circulars/42173. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40242] IceCube alert 141456_888784 retraction
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42172 SUBJECT: IceCube alert 141456_888784 retraction DATE: 25/10/08 23:19:08 GMT FROM: Erik Blaufuss at University of Maryland, College Park <blaufuss(a)umd.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 8 Oct 2025 at 22:35:50 UT IceCube issued an alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/141456_888784.amon) reporting the detection of a neutrino candidate event with a moderate chance of being of astrophysical origin. Upon further examination by the IceCube collaboration, the event data was incomplete and clear classification of this event is not possible. At the time of this alert, the detector was operating with several portions of the detector removed from data taking due to hardware issues. Normally, these periods of operation are excluded from generating alerts. We apologize for any confusion this error may have caused. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/42172. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40241] IceCube Alert 251008.94: Global MASTER-Net observations report
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42171 SUBJECT: IceCube Alert 251008.94: Global MASTER-Net observations report DATE: 25/10/08 23:00:30 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the IceCube Alert 251008.94 (trigger No 888784,02h 10m 30.00s , -37d 22m 58.8s, R=0.82) errorbox 12 sec after notice time and 77 sec after trigger time at 2025-10-08 22:37:08 UT, with upper limit up to 14.9 mag. The observations began at zenith distance = 80 deg. The sun altitude is -47.1 deg. The galactic latitude b = -70 deg., longitude l = 248 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3010374 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 87 | 2025-10-08 22:37:08 | MASTER-Kislovodsk | (02h 10m 07.45s , -37d 12m 08.1s) | P- | 20 | 13.5 | 87 | 2025-10-08 22:37:08 | MASTER-Kislovodsk | (02h 10m 20.29s , -36d 49m 52.3s) | P| | 20 | 14.0 | 127 | 2025-10-08 22:37:48 | MASTER-Kislovodsk | (02h 10m 07.61s , -37d 12m 10.0s) | P- | 20 | 13.6 | 127 | 2025-10-08 22:37:48 | MASTER-Kislovodsk | (02h 10m 20.57s , -36d 49m 54.1s) | P| | 20 | 14.1 | 172 | 2025-10-08 22:38:27 | MASTER-Kislovodsk | (02h 10m 07.83s , -37d 12m 11.4s) | P- | 30 | 13.5 | 172 | 2025-10-08 22:38:27 | MASTER-Kislovodsk | (02h 10m 20.85s , -36d 49m 55.6s) | P| | 30 | 14.4 | 227 | 2025-10-08 22:39:17 | MASTER-Kislovodsk | (02h 10m 08.11s , -37d 12m 12.6s) | P- | 40 | 14.1 | 227 | 2025-10-08 22:39:17 | MASTER-Kislovodsk | (02h 10m 21.18s , -36d 49m 56.7s) | P| | 40 | 14.5 | 291 | 2025-10-08 22:40:17 | MASTER-Kislovodsk | (02h 10m 08.36s , -37d 12m 14.0s) | P- | 50 | 13.9 | 292 | 2025-10-08 22:40:17 | MASTER-Kislovodsk | (02h 10m 21.52s , -36d 49m 58.2s) | P| | 50 | 14.4 | 366 | 2025-10-08 22:41:27 | MASTER-Kislovodsk | (02h 10m 08.70s , -37d 12m 15.9s) | P- | 60 | 14.1 | 366 | 2025-10-08 22:41:27 | MASTER-Kislovodsk | (02h 10m 21.96s , -36d 49m 59.9s) | P| | 60 | 14.6 | 456 | 2025-10-08 22:42:47 | MASTER-Kislovodsk | (02h 10m 09.11s , -37d 12m 17.3s) | P- | 80 | 14.1 | 456 | 2025-10-08 22:42:47 | MASTER-Kislovodsk | (02h 10m 22.44s , -36d 50m 01.3s) | P| | 80 | 14.8 | 566 | 2025-10-08 22:44:27 | MASTER-Kislovodsk | (02h 10m 09.54s , -37d 12m 20.0s) | P- | 100 | 14.0 | 566 | 2025-10-08 22:44:27 | MASTER-Kislovodsk | (02h 10m 22.97s , -36d 50m 03.9s) | P| | 100 | 14.6 | 696 | 2025-10-08 22:46:26 | MASTER-Kislovodsk | (02h 10m 10.14s , -37d 12m 22.6s) | P- | 120 | 14.1 | 696 | 2025-10-08 22:46:27 | MASTER-Kislovodsk | (02h 10m 23.63s , -36d 50m 06.1s) | P| | 120 | 14.7 | 836 | 2025-10-08 22:48:46 | MASTER-Kislovodsk | (02h 10m 10.74s , -37d 12m 24.9s) | P- | 120 | 14.1 | 836 | 2025-10-08 22:48:46 | MASTER-Kislovodsk | (02h 10m 24.29s , -36d 50m 07.9s) | P| | 120 | 14.7 | 975 | 2025-10-08 22:51:06 | MASTER-Kislovodsk | (02h 10m 11.30s , -37d 12m 26.4s) | P- | 120 | 14.1 | 976 | 2025-10-08 22:51:06 | MASTER-Kislovodsk | (02h 10m 24.93s , -36d 50m 08.8s) | P| | 120 | 14.8 | 1115 | 2025-10-08 22:53:25 | MASTER-Kislovodsk | (02h 10m 11.90s , -37d 12m 27.9s) | P- | 120 | 14.1 | 1115 | 2025-10-08 22:53:26 | MASTER-Kislovodsk | (02h 10m 25.56s , -36d 50m 10.6s) | P| | 120 | 14.9 | The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42171. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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[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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[vsnet-grb-info 40224] GRB 251006B: Insight-HXMT detection
by GCN Circulars 08 Oct '25

08 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42155 SUBJECT: GRB 251006B: Insight-HXMT detection DATE: 25/10/08 04:38:08 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Yue Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-10-06T20:05:04.350 (T0), Insight-HXMT/HE detected the burst GRB 251006B, which is also detected by Fermi/GBM (Fermi GBM team, GCN#42131), EP (Yin et al., GCN#42137) and SVOM/GRM (Wang et al., GCN#42139). The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 4.6 +1.1/-0.8 s. The 1s peak rate, measured from T0-0.1 s, is 3694 cnts/sec. The total counts from this burst is 5990 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251006B.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/42155. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40223] GRB 251007A: SVOM/C-GFT optical observations
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42154 SUBJECT: GRB 251007A: SVOM/C-GFT optical observations DATE: 25/10/07 23:55:44 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei Qiu(NAOC), Jing Wang (NAOC), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 251007A detected by Swift/BAT (Ambrosi et al., GCN 42146) and Glowbug (Cheung et al., GCN 42151) with LATIOS on SVOM/C-GFT. Observations started at 2025-10-07T19:37:48 UTC, ~50 seconds after the trigger. The optical counterpart reported by Swift/UVOT (Ambrosi et al., GCN 42146) is clearly detected in our i-band images. The magnitude is : |[date-obs|mid-time] | Mid_t-T0(s) | exposure time (s) | band | mag (AB) | mag_err | |---------------------|-------------|-------------------|------|----------|---------| | 2025-10-07T19:37:53 | 55 | 10 | i | 16.41 | 0.13 | The photometry was calibrated against the UCAC4 catalogue, and no correction for Galactic dust extinction was applied. We thank the observation assistants Chunlei Guo and Shuai Liu at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/42154. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40222] GRB 251005C: PRIME J-band upper limit
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42153 SUBJECT: GRB 251005C: PRIME J-band upper limit DATE: 25/10/07 23:04:57 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva(a)uniroma1.it> M. El Kabir (U Rome), O. Guiffreda (UMD), N. Passaleva (U Rome), J. Durbak (UMD), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) Following the Swift/BAT detection and Swift/XRT localization of an uncatalogued source (Page et al, GCN 42113), we observed the transient field in J filter with PRIME ~32.9 hours after the initial BAT trigger. Using Two Micron All Sky Survey (2MASS) for preliminary calibration we do not detect any uncatalogued source down to J>20.2 AB (3-sigma) not corrected for galactic extinction at the position of the candidates reported by Swift/XRT (Goad et al. GCN 42116), and SVOM/VT (Palmerio et al., GCN 42123). PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/42153. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40221] Swift GRB 251007B: Global MASTER-Net observations report
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42152 SUBJECT: Swift GRB 251007B: Global MASTER-Net observations report DATE: 25/10/07 22:37:00 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 251007B ( A. Melandri et al., GCN 42147) errorbox 9413 sec after notice time and 9658 sec after trigger time at 2025-10-07 22:24:05 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 83 deg. The sun altitude is -52.3 deg. The galactic latitude b = -5 deg., longitude l = 222 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3009588 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 9688 | MASTER-SAAO | C | 60 | 17.1 | 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/42152. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40220] GRB 251007A: Glowbug gamma-ray detection
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42151 SUBJECT: GRB 251007A: Glowbug gamma-ray detection DATE: 25/10/07 22:35:45 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251007A, which was also detected by Swift/BAT (GCN 42146) and CALET (Trigger 1443900615). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-07 19:37:09.088 with a duration of 65.5 s and a total significance of about 137.8 sigma. The Glowbug light curve is dominated by a triple-peaked structure spanning ~ T0+40s to +60s corresponding to the peak emission observed by Swift/BAT and CALET. Note the Glowbug onset time is ~11 s after the Swift/BAT trigger time (19:36:58). A search of the Glowbug data for emission at the Swift/BAT T0 was inconclusive. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was recently removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42151. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40219] GRB 251007B: SVOM/C-GFT upper limit
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42150 SUBJECT: GRB 251007B: SVOM/C-GFT upper limit DATE: 25/10/07 22:19:37 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei Qiu(NAOC), Jing Wang (NAOC), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC), N. A. Webb (IRAP), O. Godet (IRAP) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 251007B (SVOM burst-id sb25100703) detected by Swfit/BAT (Melandri et al. GCN 42147) and SVOM/ECLAIRs (Webb et al., GCN 42148) with LATIOS on SVOM/C-GFT. Observations started at 2025-10-07T19:44:29 UTC, ~83 seconds after the trigger. A series of g, r, and i band images were obtained. No credible candidate was detected within the error box provided by XRT (Melandri et al. GCN 42147) in our images after preliminary processing, the three sigma upper limits are: | Mid_t - T0 (s) | Exposure Time (s) | Band | Upper Limit (AB) | |----------------|-------------------|------|------------------| | 113 | 6×10 | i | 18.50 | | 248 | 18x10 | i | 18.90 | The photometry was calibrated with UCAC4 catalogue. Magnitudes were not corrected for dust extinction. We thank the observation assistants Chunlei Guo and Shuai Liu at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/42150. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40218] Swift GRB 251007A: Global MASTER-Net observations report
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42149 SUBJECT: Swift GRB 251007A: Global MASTER-Net observations report DATE: 25/10/07 21:52:44 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB 251007A ( E. Ambrosi et al., GCN 42146) errorbox 7658 sec after notice time and 7679 sec after trigger time at 2025-10-07 21:44:57 UT, with upper limit up to 15.8 mag. The observations began at zenith distance = 84 deg. The sun altitude is -51.3 deg. The galactic latitude b = 32 deg., longitude l = 203 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3009554 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 7770 | MASTER-Kislovodsk | C | 180 | 15.8 | 7770 | MASTER-Kislovodsk | C | 180 | 14.2 | 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/42149. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40217] GRB 251007B: SVOM detection of a faint burst
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42148 SUBJECT: GRB 251007B: SVOM detection of a faint burst DATE: 25/10/07 20:37:26 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> N. A. Webb, O. Godet, S. Guillot (IRAP), F. Lacreu (IAP) report on behalf of the SVOM mission team At 2025-10-07T19:43:23 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251007B (SVOM burst-id sb25100703), also detected by Swift/BAT (GCN #42147, Melandri et al. 2025). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 7 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.53 in the [8-50] keV energy band over a time window of 20.40 seconds starting at 2025-10-07T19:42:57. The localization of the best alert is R.A., Dec. 101.997, -10.279 degrees: R.A. (J2000) = 6h47m59.29s Dec. (J2000) = -10d16m42.81s with a 90% confidence level (C.L.) radius of 8.33 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a single peak structure with a T90 duration of about 23.26 (-8.032 +4.41) s. The platform did not slew to the source. No observations could be performed in the X-rays by SVOM/MXT nor in the optical with SVOM/VT for the time being. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Natalie Webb: natalie.webb(a)irap.omp.eu. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42148. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40216] GRB 251007B: Swift detection of a burst
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42147 SUBJECT: GRB 251007B: Swift detection of a burst DATE: 25/10/07 20:05:03 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> A. Melandri (INAF-OAR), E. Ambrosi (INAF-IASFPA), A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), R. Gupta (NASA GSFC), N. J. Klingler (GSFC/UMBC/CRESSTII), N. P. M. Kuin (UCL-MSSL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 19:43:06 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251007B (trigger=1402467). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 102.117, -10.303 which is RA(J2000) = 06h 48m 28s Dec(J2000) = -10d 18' 11" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Due to the continued on-board processing of the previous burst (GRB 251007A) the BAT lightcurve is not immediately available. The XRT began observing the field at 19:45:35.0 UT, 148.2 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 102.13232, -10.30328 which is equivalent to: RA(J2000) = 06h 48m 31.76s Dec(J2000) = -10d 18' 11.8" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 54 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. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 5.99 x 10^21 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 150 seconds with the White filter starting 151 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image processing FAILED because of no aspect solution. Results from the list of sources generated on-board are not available at this time. No correction has been made for the expected extinction corresponding to E(B-V) of 0.785. Burst Advocate for this burst is A. Melandri (andrea.melandri AT inaf.it). 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/42147. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40215] GRB 251007A: Swift detection of a burst with an optical counterpart
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42146 SUBJECT: GRB 251007A: Swift detection of a burst with an optical counterpart DATE: 25/10/07 19:53:26 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> E. Ambrosi (INAF-IASFPA), A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), R. Gupta (NASA GSFC), N. J. Klingler (GSFC/UMBC/CRESSTII), N. P. M. Kuin (UCL-MSSL), A. Melandri (INAF-OAR), M. J. Moss (GSFC), K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 19:36:58 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251007A (trigger=1402466). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 128.173, +21.823 which is RA(J2000) = 08h 32m 42s Dec(J2000) = +21d 49' 24" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with an initial sequence of peaks followed by a larger complex peak with a total duration of about 100 sec. The peak count rate was ~12000 counts/sec (15-350 keV), at ~56 sec after the trigger. The XRT began observing the field at 19:38:07.4 UT, 69.4 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 128.1775, 21.8138 which is equivalent to: RA(J2000) = 08h 32m 42.60s Dec(J2000) = +21d 48' 49.7" with an uncertainty of 5.4 arcseconds (radius, 90% containment). This location is 36 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. UVOT took a finding chart exposure of 150 seconds with the White filter starting 78 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 08:32:42.40 = 128.17665 DEC(J2000) = +21:48:46.1 = 21.81280 with a 90%-confidence error radius of about 0.63 arc sec. This position is 4.6 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.38 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.039. Burst Advocate for this burst is E. Ambrosi (elena.ambrosi AT inaf.it). 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/42146. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40214] GRB 250702B/EP250702a: JWST/NIRCam Observations
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42145 SUBJECT: GRB 250702B/EP250702a: JWST/NIRCam Observations DATE: 25/10/07 18:49:45 GMT FROM: Huei Sears at Rutgers University <huei.sears(a)rutgers.edu> H. Sears (Rutgers University), P. K. Blanchard (Harvard), R. Chornock (UC Berkeley), Nayana AJ (UC Berkeley), T. Ahumada (Caltech), K. D. Alexander (Arizona), I. Andreoni, A. Anumarlapudi, J. Carney (UNC), J. Freeburn (UNC), O. Graur (Portsmouth), X. J. Hall (CMU), E. Hammerstein (UC Berkeley), S. W. Jha (Rutgers), M. Kasliwal (Caltech), T. Laskar (Utah), R. Margutti (UC Berkeley), B. O’Connor (CMU), D. Pasham (MIT), I. Sfaradi (UC Berkeley), and Y. Yao (UC Berkeley) report: We obtained imaging of the field of GRB 250702B/EP250702a (GCNs 40883, 40886, 40890, 40906) with JWST/NIRCam under DD program 9447 (PI: H. Sears) starting at 2025-Oct-05 02:05:52 UT (~ 95 days post Fermi Gamma-ray trigger). The images were taken in the F150W, F200W, F277W, F356W, and F444W filters with exposure times of 10,049; 5024; 5024; 5024; and 5024 s, respectively. The host galaxy of the transient has a complex morphology in the short-wavelength filters, F150W and F200W. The prominent separation between two brighter nuclear regions seen in the Hubble Space Telescope (HST) F160W imaging (A. Levan et al. 2025, ApJL, 990, L28; J. Carney et al. 2025, arXiv: 2509.22784) is also visible at these shorter wavelengths. In the long wavelength filters, however, the galaxy has a smooth profile, including near the nucleus. This morphology supports the interpretation that the host is a single system with a prominent dust lane in a disk viewed nearly edge-on. Visual inspection reveals emission near the position of the transient in F150W and F200W that is not apparent in the longer wavelength filters. This excess emission is coincident with the excess flux noted in the HST F160W imaging (A. Levan et al. 2025, ApJL, 990, L28; J. Carney et al. 2025, arXiv: 2509.22784). The associated color and morphology suggests emission from an underlying star-forming region rather than solely from the transient. We use GALFIT to subtract two Sérsic components for the long-wavelength + F200W filters and one component for the F150W filter. To place limits on any transient flux, we additionally include one point source component in all filters fixed at the location of the HAWK-I H+K source as reported in A. Levan et al. 2025, ApJL, 990, L28; R.A. (J2000) = 18h 58m 45.s 57, decl. (J2000) = –07d 52 26.2. While the excess flux noticed in the F150W and F200W imaging is ~0.15’’ offset from the HAWK-I position, we believe this is likely to be due to imprecise absolute astrometry. For completeness, we report photometry for the transient at both locations. At the HAWK-I location, we report preliminary host-galaxy subtracted, 3-sigma upper-limits of m_F444W > 25.5 AB, m_F356W > 25.7 AB, m_F277W > 26.2 AB, m_F200W > 27.8 AB, and m_F150W > 28.6 AB (faint with high uncertainty). If, instead, we force the location of the transient to be at the excess flux noted in F150W and F200W, we report preliminary detections of m_F200W = 27.97 +/- 0.32 AB and m_F150W = 29.01 +/- 0.43 AB and find similar limits in the long-wavelength filters. Of note, these magnitudes are not corrected for Galactic nor host extinction. Further analysis is ongoing. We thank STScI staff members Alison Vick, Ben Sunnquist, and the entire JWST team for the successful implementation of this DD program. View this GCN Circular online at https://gcn.nasa.gov/circulars/42145. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40213] GRB 251006A: Swift/BAT-GUANO subthreshold detection of a short burst
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42144 SUBJECT: GRB 251006A: Swift/BAT-GUANO subthreshold detection of a short burst DATE: 25/10/07 17:49:15 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Samuele Ronchini (GSSI), Aaron Tohuvavohu (Caltech), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report: Swift/BAT did not localize GRB 251006A onboard (T0: 2025-10-06T13:27:35.03 UTC, Fermi/GBM trig 781450060, Glowbug GCN 42130) The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 7.1 in a 0.256 s analysis time bin, starting at T0 - 0.064 s. This corresponds to a FAR ~ 9e-4 s. Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep) The 90% credible area is 16,319 deg2 and the 50% credible area is 6,346 deg2. The integrated probability inside the coded field of view is 5%. The NITRATES skymap is very large but is consistent with the Fermi localization reported in the final position notice (GCN 42124). A plot of the probability skymap can be viewed here: [skymap_plot](https://guano.swift.psu.edu/trigger_report?id=781450091/#:~:te… The probability skymap file can be downloaded from the link here [skymap_fits_file](https://guano.swift.psu.edu/files/781450091/0_n_PROBMAP) [joint_skymap_fits_file](https://guano.swift.psu.edu/files/781450091/0_n_JOI… Instructions on how to read and manipulate this map can be found here: https://guano.swift.psu.edu/documentation More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=781450091 GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/ View this GCN Circular online at https://gcn.nasa.gov/circulars/42144. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40212] GRB 251005B: Glowbug gamma-ray detection
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42143 SUBJECT: GRB 251005B: Glowbug gamma-ray detection DATE: 25/10/07 15:50:03 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251005B, which was also detected by Fermi/GBM (GCN 42112). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-05 14:27:57.168 with a duration of 6.1 s and a total significance of about 14.1 sigma. The Glowbug onset is ~38 s after the Fermi/GBM trigger time (14:27:19) and corresponds to the second, brighter peak seen in the Fermi/GBM light curve. A search of the Glowbug data for the initial fainter peak at the Fermi/GBM T0 was inconclusive. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was recently removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42143. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40211] EP251003a: LCO and VST fading optical counterpart
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42142 SUBJECT: EP251003a: LCO and VST fading optical counterpart DATE: 25/10/07 14:34:45 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), J. A. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (U. Leicester), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), F. E. Bauer (SSI and UTA), and J. A. Chacón (PUC) report on behalf of a larger collaboration: We observed the location of EP251003a (Liu et al., GCN 42107) with the Sinistro instrument mounted on the 1-m telescopes at Cerro Tololo Inter-American Observatory, available via the LCO network. Six 200 s exposures were obtained in the SDSS i filter starting at 2025-10-05 UT 07:16:29 (~35.1 hr post trigger). Within the WXT and FXT error circles (Liu et al., GCN 42107), we identify a new source. Calibrated to nearby stars from the Pan-STARRS catalog, we measure a magnitude i = 21.6 +/- 0.2 (AB), not corrected for Galactic extinction. No corresponding object is visible in the Legacy Survey down to an AB magnitude of i > 24.2. We obtained an additional observation with the VLT Survey Telescope (VST). Six exposures of 300 s each were obtained in the SDSS i filter as well ten 200 s exposures in the SDSS z filter, starting at 2025-10-06 UT 06:47:12 (~58.6 hr post trigger). The counterpart identified in the LCO image is again detected, and we measure a magnitude of i = 22.87 +/- 0.07 and z = 23.23 +/- 0.14 (AB). Given the significant fading, the consistency with the X-ray localization, and the lack of a bright archival counterpart, we consider this source as the likely counterpart of EP251003a. The most accurate coordinates of the counterpart as measured from the VST image are: RA(J2000): 03:47:40.99 DEC(J2000): -10:55:55.0 We estimate an uncertainty of 0.2" in both RA and Dec. View this GCN Circular online at https://gcn.nasa.gov/circulars/42142. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40210] GRB 251006B/EP251006a: SVOM/VT optical candidate
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42141 SUBJECT: GRB 251006B/EP251006a: SVOM/VT optical candidate DATE: 25/10/07 14:11:15 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Z. H. Yao, 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), Z. Q. Wang, K. Liu (GXU) report on behalf of the SVOM/VT team. SVOM/VT conducted ToO follow-up observations of GRB 251006B / EP251006a (Fermi GBM Team, GCN 42131; Yin et al. GCN 42137; Wang et al., GCN 42139). The observation started on 2025-10-07T09:37:56 UT (i.e. 13.56 hour after Fermi trigger time) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. Within the error box of EP-FXT source 2 (Yin et al., GCN 42140), an uncatalogued source was detected, compared to the Legacy survey. The position is at R.A., Dec. = 40.518487, -6.034955 degrees, equivalent to: R.A. (J2000) = 02:42:04.43 Dec. (J2000) = -06:02:05.8 with an uncertainty of 0.5 arcsec. The magnitudes of the candidate are given below: Mid_time Band Exposure Time Magnitude (AB) 13.5672 hour VT_B 41*70 sec 22.37+/-0.11 mag 13.5672 hour VT_R 39*70 sec 22.12+/-0.12 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/42141. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40209] GRB 251006B/EP251006a: EP-FXT follow-up observation
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42140 SUBJECT: GRB 251006B/EP251006a: EP-FXT follow-up observation DATE: 25/10/07 13:03:20 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 follow-up observation of GRB 251006B/EP251006a (GCN 42131, GCN 42137, GCN 42139) at 2025-10-07T06:50:56 (UTC), about 11 hours after the WXT detection, with an exposure time of 2.7 ks. The source was also followed by several optical telescopes (GCN 42133, GCN 42138). Two uncatalogued sources were detected within the WXT error circle. Preliminary analyses on these sources are automatically conducted, and the details are listed as follows. Source 1: EPF_J024205.3-055701 RA (J2000): 40.5219 Dec (J2000): -5.9501 Flux: 3.25 x 10^-13 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 9.45 x 10^-14 erg/s/cm^2 (1 sigma) Source 2: EPF_J024204.7-060206 RA (J2000): 40.5194 Dec (J2000): -6.0350 Flux: 3.52 x 10^-12 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 4.30 x 10^-13 erg/s/cm^2 (1 sigma) 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/42140. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40208] GRB 251006B: SVOM/GRM observation
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42139 SUBJECT: GRB 251006B: SVOM/GRM observation DATE: 25/10/07 11:08:42 GMT FROM: Yue Wang <m18509381757(a)163.com> SVOM/GRM team: Yue Wang, Chen-Wei Wang, Wen-Jun Tan, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Feliu Lacreu (IAP), Olivier GODET (IRAP), Frédéric Piron (LUPM) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 251006B (SVOM trigger reference: sb25100602) at 2025-10-06T20:05:08.000 (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #42131). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of two pulses with a T90 of 6.2 +0.2/-0.1 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251006B.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 40.5, Dec = -4.0, GCN #42131), is located at about 40.5 degrees from the SVOM optical axis, which is inside the ECLAIRs field of view. But ECLAIRs was not collecting data at the time of this burst. With this localization, the time-averaged spectrum from T0-5 to T0+5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.76 +0.03/-0.03 and the cutoff energy, parameterized as Epeak, is 433 +27/-24 keV. The event fluence (10-1000 keV) in this time interval is (2.02 +0.05/-0.05)E-05 erg/cm^2. The localization of GRB 251006B in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251006B_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/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42139. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40207] GRB 251006B: COLIBRÍ optical upper limit
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42138 SUBJECT: GRB 251006B: COLIBRÍ optical upper limit DATE: 25/10/07 09:36:59 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Jean-Grégoire Ducoin (CPPM), Diego López-Cámara (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), 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 Fermi GRB 251006B (Fermi GBM Team, GCN Circ. 42131, Preis et al., GCN Circ 42132, Yin et al., GCN Circ. 42137) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-07T06:00:50 to 06:19:48 UTC (from 9.93 to 10.25 hours after the trigger) and obtained 13 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline 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 any new source at the EP-WXT source position (Yin et al., GCN Circ. 42137) down to the following 5-sigma limit: r > 21.0 z > 20.6 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/42138. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40206] GRB 251006B/EP251006a: EP-WXT detection
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42137 SUBJECT: GRB 251006B/EP251006a: EP-WXT detection DATE: 25/10/07 03:30:56 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: We report on the detection of a fast X-ray transient, designated EP251006a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at T0 = 2025-10-06T20:05:04 (UTC). The position of the source is R.A. = 40.505 deg, DEC = -5.989 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic). The trigger time and position of this X-ray transient are consistent with that of GRB 251006B (GCN 42131, GCN 42132). The analysis of the WXT data shows that the event lasted for about 100 seconds with a two-pulse main emission within T0 - T0 + 10 s followed by a much weaker tail. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.98 x 10^20 cm^-2 and a photon index of 1.28 (-0.60/+0.64). The derived average unabsorbed 0.5-4 keV flux is 1.61 (-0.72/+0.50) x 10^-10 erg/s/cm^2. The peak flux is around 9.09 x 10^-9 erg/s/cm^2 with a fixed Galactic hydrogen column density of 2.98 x 10^20 cm^-2 and a photon index of 1.09 (-0.76/+0.84). 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/42137. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40205] GRB 251005C: SVOM/VT optical fading
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42136 SUBJECT: GRB 251005C: SVOM/VT optical fading DATE: 25/10/07 03:27:51 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. A second ToO observation from SVOM/VT was performed to the field of GRB 251005C (Page et al., GCN 42113; Smith et al., GCN 42118; Arya et al., GCN 42122; Luo et al., GCN 42135) which stared at 2025-10-06T17:36:01 UTC, I.e., 25.5 hours post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical candidate (Palmerio et al. , GCN 42123; Yadav et al., GCN 42127; Watson et al., GCN 42129) was detected in VT_R stacked image at the mid time of 27.4 hours post trigger with the brightness of VT_R~23.3+/-0.2 mag. Combining earlier magnitudes from VT, the source was fading with a power-law temporal slope of about -0.7. 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/42136. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40204] GRB 251005C: SVOM/GRM observation of a likely short GRB
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42135 SUBJECT: GRB 251005C: SVOM/GRM observation of a likely short GRB DATE: 25/10/07 03:12:49 GMT FROM: Xinghao Luo at SVOM/GRN <2952704891(a)qq.com> SVOM/GRM team: Xing-Hao Luo, Chen-Wei Wang, Zheng-Hang Yu, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Daigne (IAP), Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 251005C(SVOM trigger reference: sb25100502) at 2025-10-05T16:06:54.000 UTC(T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#42118) and Swift/BAT (K. L. Page et al., GCN#42113) 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 1.6 +0.6/-0.3 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251005C.png In addition, the position of this burst, as determined by Swift/XRT (RA=75.673 , DEC=16.882, GCN#42116), is located at about 51 degrees form the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-0.4 to T0+1.6 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.81 +0.16/-0.14 and the cutoff energy, parameterized as Epeak, is 900 +547/-285 keV. The event fluence (10-1000 keV) in this time interval is (2.17 +0.19/-0.18)E-06 erg/cm^2. The localization of GRB 251005C in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251005C_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: Xing-Hao Luo (2952704891(a)qq.com) View this GCN Circular online at https://gcn.nasa.gov/circulars/42135. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40203] LIGO/Virgo/KAGRA S251006dd: Identification of a GW compact binary merger candidate
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42134 SUBJECT: LIGO/Virgo/KAGRA S251006dd: Identification of a GW compact binary merger candidate DATE: 25/10/07 00:10:26 GMT FROM: yamazaki.ryo.77(a)gmail.com The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S251006dd during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-10-06 23:37:17.979 UTC (GPS time: 1443829055.979). The candidate was found by the Aframe [1], MBTA [2], PyCBC Live [3], and SPIIR [4] analysis pipelines. S251006dd is an event of interest because its false alarm rate, as estimated by the online analysis, is 5.4e-16 Hz, or about one in 1e8 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S251006dd The classification of the GW signal, in order of descending probability, is BBH (>99%), NSBH (<1%), Terrestrial (<1%), or BNS (<1%). Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [5] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [5] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 14%. The source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [6], distributed via GCN and SCiMMA notices about 26 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [6], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 109 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 706 +/- 151 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010 [2] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [3] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [4] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [5] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [6] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/42134. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40202] Fermi GRB 251006B: Global MASTER-Net observations report
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42133 SUBJECT: Fermi GRB 251006B: Global MASTER-Net observations report DATE: 25/10/06 21:16:05 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 251006B ( Fermi GBM team, GCN 42131) errorbox 532 sec after notice time and 575 sec after trigger time at 2025-10-06 20:14:39 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 63 deg. The sun altitude is -41.2 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 251006B errorbox 545 sec after notice time and 587 sec after trigger time at 2025-10-06 20:14:51 UT, with upper limit up to 14.9 mag. The observations began at zenith distance = 59 deg. The sun altitude is -51.1 deg. MASTER-Tunka robotic telescope located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 251006B errorbox 563 sec after notice time and 606 sec after trigger time at 2025-10-06 20:15:10 UT, with upper limit up to 16.7 mag. The observations began at zenith distance = 58 deg. The sun altitude is -28.3 deg. The galactic latitude b = -54 deg., longitude l = 177 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3008721 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 605 | 2025-10-06 20:14:39 | MASTER-SAAO | (02h 39m 49.30s , -04d 20m 36.1s) | C | 60 | 17.6 | 665 | 2025-10-06 20:14:39 | MASTER-SAAO | (02h 39m 49.30s , -04d 20m 36.1s) | C | 180 | 18.4 | Coadd 605 | 2025-10-06 20:14:39 | MASTER-SAAO | (02h 37m 57.07s , -04d 05m 19.3s) | C | 60 | 17.5 | 665 | 2025-10-06 20:14:39 | MASTER-SAAO | (02h 37m 57.07s , -04d 05m 19.3s) | C | 180 | 18.2 | Coadd 648 | 2025-10-06 20:14:51 | MASTER-Kislovodsk | (02h 39m 53.89s , -04d 03m 53.7s) | P| | 120 | 13.3 | 648 | 2025-10-06 20:14:51 | MASTER-Kislovodsk | (02h 39m 44.13s , -03d 40m 31.4s) | P- | 120 | 14.9 | 609 | 2025-10-06 20:15:10 | MASTER-Tunka | (02h 42m 02.24s , -03d 51m 31.9s) | C | 5 | 16.2 | 614 | 2025-10-06 20:15:10 | MASTER-Tunka | (02h 42m 02.24s , -03d 51m 31.9s) | C | 15 | 16.7 | Coadd 609 | 2025-10-06 20:15:10 | MASTER- | (02h 41m 39.21s , -03d 46m 29.9s) | C | 5 | 15.9 | 618 | 2025-10-06 20:15:18 | MASTER- | (02h 41m 39.20s , -03d 46m 30.4s) | C | 5 | 15.8 | 618 | 2025-10-06 20:15:18 | MASTER-Tunka | (02h 42m 02.24s , -03d 51m 32.3s) | C | 5 | 16.1 | 627 | 2025-10-06 20:15:27 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 32.7s) | C | 5 | 16.1 | 627 | 2025-10-06 20:15:28 | MASTER- | (02h 41m 39.22s , -03d 46m 30.9s) | C | 5 | 15.9 | 639 | 2025-10-06 20:15:40 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 33.0s) | C | 5 | 16.1 | 644 | 2025-10-06 20:15:40 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 32.9s) | C | 15 | 16.6 | Coadd 639 | 2025-10-06 20:15:40 | MASTER- | (02h 41m 39.21s , -03d 46m 31.1s) | C | 5 | 15.9 | 652 | 2025-10-06 20:15:52 | MASTER-Tunka | (02h 42m 02.24s , -03d 51m 33.2s) | C | 5 | 16.0 | 652 | 2025-10-06 20:15:52 | MASTER- | (02h 41m 39.21s , -03d 46m 31.6s) | C | 5 | 15.8 | 684 | 2025-10-06 20:15:58 | MASTER-SAAO | (02h 39m 49.23s , -04d 20m 36.1s) | C | 60 | 17.6 | 684 | 2025-10-06 20:15:58 | MASTER-SAAO | (02h 37m 56.96s , -04d 05m 19.4s) | C | 60 | 17.6 | 661 | 2025-10-06 20:16:01 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 33.4s) | C | 5 | 16.0 | 661 | 2025-10-06 20:16:01 | MASTER- | (02h 41m 39.22s , -03d 46m 31.7s) | C | 5 | 15.9 | 669 | 2025-10-06 20:16:10 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 33.8s) | C | 5 | 16.0 | 674 | 2025-10-06 20:16:10 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 33.8s) | C | 15 | 16.6 | Coadd 669 | 2025-10-06 20:16:10 | MASTER- | (02h 41m 39.22s , -03d 46m 32.1s) | C | 5 | 15.8 | 678 | 2025-10-06 20:16:18 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 34.2s) | C | 5 | 16.1 | 678 | 2025-10-06 20:16:18 | MASTER- | (02h 41m 39.22s , -03d 46m 32.5s) | C | 5 | 15.8 | 686 | 2025-10-06 20:16:27 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 34.3s) | C | 5 | 16.0 | 686 | 2025-10-06 20:16:27 | MASTER- | (02h 41m 39.23s , -03d 46m 32.7s) | C | 5 | 15.9 | 715 | 2025-10-06 20:16:55 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 35.5s) | C | 5 | 16.1 | 720 | 2025-10-06 20:16:55 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 35.4s) | C | 15 | 16.5 | Coadd 715 | 2025-10-06 20:16:55 | MASTER- | (02h 41m 39.23s , -03d 46m 33.7s) | C | 5 | 15.9 | 723 | 2025-10-06 20:17:03 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 35.7s) | C | 5 | 16.0 | 723 | 2025-10-06 20:17:03 | MASTER- | (02h 41m 39.22s , -03d 46m 34.0s) | C | 5 | 15.9 | 787 | 2025-10-06 20:17:11 | MASTER-Kislovodsk | (02h 39m 44.20s , -03d 40m 29.1s) | P- | 120 | 14.3 | 787 | 2025-10-06 20:17:11 | MASTER-Kislovodsk | (02h 39m 55.26s , -04d 03m 41.8s) | P| | 120 | 13.6 | 732 | 2025-10-06 20:17:12 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 35.8s) | C | 5 | 16.1 | 732 | 2025-10-06 20:17:13 | MASTER- | (02h 41m 39.22s , -03d 46m 34.3s) | C | 5 | 15.9 | 763 | 2025-10-06 20:17:17 | MASTER-SAAO | (02h 39m 49.17s , -04d 20m 36.1s) | C | 60 | 17.6 | 763 | 2025-10-06 20:17:17 | MASTER-SAAO | (02h 37m 56.87s , -04d 05m 19.6s) | C | 60 | 17.4 | 740 | 2025-10-06 20:17:21 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 36.1s) | C | 5 | 16.0 | 745 | 2025-10-06 20:17:21 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 36.1s) | C | 15 | 16.6 | Coadd 740 | 2025-10-06 20:17:21 | MASTER- | (02h 41m 39.22s , -03d 46m 34.5s) | C | 5 | 15.8 | 749 | 2025-10-06 20:17:29 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 36.3s) | C | 5 | 16.1 | 749 | 2025-10-06 20:17:29 | MASTER- | (02h 41m 39.21s , -03d 46m 34.8s) | C | 5 | 15.8 | 757 | 2025-10-06 20:17:38 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 36.4s) | C | 5 | 16.1 | 757 | 2025-10-06 20:17:38 | MASTER- | (02h 41m 39.21s , -03d 46m 35.1s) | C | 5 | 15.8 | 766 | 2025-10-06 20:17:46 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 36.9s) | C | 5 | 16.0 | 771 | 2025-10-06 20:17:46 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 36.9s) | C | 15 | 16.7 | Coadd 766 | 2025-10-06 20:17:46 | MASTER- | (02h 41m 39.21s , -03d 46m 35.4s) | C | 5 | 15.8 | 774 | 2025-10-06 20:17:54 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 37.2s) | C | 5 | 16.1 | 774 | 2025-10-06 20:17:54 | MASTER- | (02h 41m 39.21s , -03d 46m 35.7s) | C | 5 | 15.9 | 782 | 2025-10-06 20:18:03 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 37.2s) | C | 5 | 16.1 | 782 | 2025-10-06 20:18:03 | MASTER- | (02h 41m 39.21s , -03d 46m 36.0s) | C | 5 | 15.9 | 814 | 2025-10-06 20:18:35 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 38.1s) | C | 5 | 16.1 | 819 | 2025-10-06 20:18:35 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 38.2s) | C | 15 | 16.7 | Coadd 814 | 2025-10-06 20:18:35 | MASTER- | (02h 41m 39.20s , -03d 46m 37.1s) | C | 5 | 16.0 | 842 | 2025-10-06 20:18:36 | MASTER-SAAO | (02h 39m 49.10s , -04d 20m 36.0s) | C | 60 | 17.6 | 842 | 2025-10-06 20:18:36 | MASTER-SAAO | (02h 37m 56.77s , -04d 05m 19.7s) | C | 60 | 17.6 | 838 | 2025-10-06 20:18:59 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 38.9s) | C | 5 | 16.0 | 838 | 2025-10-06 20:18:59 | MASTER- | (02h 41m 39.22s , -03d 46m 38.0s) | C | 5 | 15.9 | 847 | 2025-10-06 20:19:07 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 39.2s) | C | 5 | 16.0 | 847 | 2025-10-06 20:19:07 | MASTER- | (02h 41m 39.20s , -03d 46m 38.2s) | C | 5 | 15.9 | 856 | 2025-10-06 20:19:17 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 39.5s) | C | 5 | 16.1 | 861 | 2025-10-06 20:19:17 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 39.5s) | C | 15 | 16.5 | Coadd 856 | 2025-10-06 20:19:17 | MASTER- | (02h 41m 39.22s , -03d 46m 38.6s) | C | 5 | 15.9 | 865 | 2025-10-06 20:19:25 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 39.7s) | C | 5 | 16.2 | 865 | 2025-10-06 20:19:25 | MASTER- | (02h 41m 39.21s , -03d 46m 38.8s) | C | 5 | 15.9 | 927 | 2025-10-06 20:19:31 | MASTER-Kislovodsk | (02h 39m 55.35s , -04d 03m 40.8s) | P| | 120 | 13.6 | 927 | 2025-10-06 20:19:31 | MASTER-Kislovodsk | (02h 39m 44.35s , -03d 40m 26.8s) | P- | 120 | 14.5 | 874 | 2025-10-06 20:19:34 | MASTER- | (02h 41m 39.21s , -03d 46m 39.1s) | C | 5 | 16.0 | 874 | 2025-10-06 20:19:34 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 40.0s) | C | 5 | 16.2 | 883 | 2025-10-06 20:19:43 | MASTER- | (02h 41m 39.21s , -03d 46m 39.1s) | C | 5 | 16.0 | 883 | 2025-10-06 20:19:43 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 40.1s) | C | 5 | 16.1 | 888 | 2025-10-06 20:19:43 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 40.1s) | C | 15 | 16.7 | Coadd 892 | 2025-10-06 20:19:52 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 40.3s) | C | 5 | 16.1 | 892 | 2025-10-06 20:19:52 | MASTER- | (02h 41m 39.21s , -03d 46m 39.4s) | C | 5 | 16.0 | 900 | 2025-10-06 20:20:01 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 40.5s) | C | 5 | 16.1 | 900 | 2025-10-06 20:20:01 | MASTER- | (02h 41m 39.22s , -03d 46m 39.8s) | C | 5 | 15.9 | 928 | 2025-10-06 20:20:29 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 41.5s) | C | 5 | 16.2 | 933 | 2025-10-06 20:20:29 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 41.5s) | C | 15 | 16.7 | Coadd 928 | 2025-10-06 20:20:29 | MASTER- | (02h 41m 39.20s , -03d 46m 40.5s) | C | 5 | 15.9 | 936 | 2025-10-06 20:20:37 | MASTER-Tunka | (02h 42m 02.24s , -03d 51m 41.8s) | C | 5 | 16.2 | 937 | 2025-10-06 20:20:37 | MASTER- | (02h 41m 39.20s , -03d 46m 40.8s) | C | 5 | 15.9 | 946 | 2025-10-06 20:20:47 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 42.0s) | C | 5 | 16.2 | 946 | 2025-10-06 20:20:47 | MASTER- | (02h 41m 39.22s , -03d 46m 41.0s) | C | 5 | 16.0 | 956 | 2025-10-06 20:20:57 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 42.3s) | C | 5 | 16.1 | 961 | 2025-10-06 20:20:57 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 42.3s) | C | 15 | 16.7 | Coadd 956 | 2025-10-06 20:20:57 | MASTER- | (02h 41m 39.21s , -03d 46m 41.3s) | C | 5 | 16.0 | 965 | 2025-10-06 20:21:05 | MASTER- | (02h 41m 39.22s , -03d 46m 41.6s) | C | 5 | 16.0 | 965 | 2025-10-06 20:21:05 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 42.5s) | C | 5 | 16.1 | 973 | 2025-10-06 20:21:14 | MASTER-Tunka | (02h 42m 02.28s , -03d 51m 42.6s) | C | 5 | 16.1 | 973 | 2025-10-06 20:21:14 | MASTER- | (02h 41m 39.23s , -03d 46m 41.8s) | C | 5 | 16.0 | 982 | 2025-10-06 20:21:22 | MASTER-Tunka | (02h 42m 02.28s , -03d 51m 42.9s) | C | 5 | 16.1 | 987 | 2025-10-06 20:21:22 | MASTER-Tunka | (02h 42m 02.28s , -03d 51m 43.0s) | C | 15 | 16.7 | Coadd 982 | 2025-10-06 20:21:22 | MASTER- | (02h 41m 39.23s , -03d 46m 41.9s) | C | 5 | 16.0 | 990 | 2025-10-06 20:21:31 | MASTER- | (02h 41m 39.23s , -03d 46m 42.3s) | C | 5 | 15.9 | 990 | 2025-10-06 20:21:31 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 43.2s) | C | 5 | 16.1 | 999 | 2025-10-06 20:21:40 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 43.6s) | C | 5 | 16.1 | 999 | 2025-10-06 20:21:40 | MASTER- | (02h 41m 39.23s , -03d 46m 42.6s) | C | 5 | 15.9 | 1008 | 2025-10-06 20:21:48 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 43.8s) | C | 5 | 16.1 | 1013 | 2025-10-06 20:21:48 | MASTER-Tunka | (02h 42m 02.28s , -03d 51m 43.8s) | C | 15 | 16.7 | Coadd 1008 | 2025-10-06 20:21:48 | MASTER- | (02h 41m 39.23s , -03d 46m 42.9s) | C | 5 | 16.0 | 1067 | 2025-10-06 20:21:50 | MASTER-Kislovodsk | (02h 39m 44.50s , -03d 40m 23.0s) | P- | 120 | 14.3 | 1067 | 2025-10-06 20:21:51 | MASTER-Kislovodsk | (02h 39m 55.40s , -04d 03m 37.6s) | P| | 120 | 13.7 | 1016 | 2025-10-06 20:21:57 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 44.0s) | C | 5 | 16.2 | 1016 | 2025-10-06 20:21:57 | MASTER- | (02h 41m 39.22s , -03d 46m 43.0s) | C | 5 | 16.0 | 1024 | 2025-10-06 20:22:05 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 44.3s) | C | 5 | 16.1 | 1024 | 2025-10-06 20:22:05 | MASTER- | (02h 41m 39.21s , -03d 46m 43.1s) | C | 5 | 16.0 | 1033 | 2025-10-06 20:22:14 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 44.6s) | C | 5 | 16.1 | 1038 | 2025-10-06 20:22:14 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 44.5s) | C | 15 | 16.6 | Coadd 1033 | 2025-10-06 20:22:14 | MASTER- | (02h 41m 39.21s , -03d 46m 43.8s) | C | 5 | 16.0 | 1042 | 2025-10-06 20:22:22 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 44.7s) | C | 5 | 16.0 | 1042 | 2025-10-06 20:22:22 | MASTER- | (02h 41m 39.20s , -03d 46m 43.9s) | C | 5 | 16.0 | 1050 | 2025-10-06 20:22:31 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 44.9s) | C | 5 | 16.1 | 1050 | 2025-10-06 20:22:31 | MASTER- | (02h 41m 39.20s , -03d 46m 44.3s) | C | 5 | 15.9 | 1059 | 2025-10-06 20:22:39 | MASTER- | (02h 41m 39.20s , -03d 46m 44.5s) | C | 5 | 16.0 | 1059 | 2025-10-06 20:22:39 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 45.1s) | C | 5 | 16.1 | 1064 | 2025-10-06 20:22:39 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 45.2s) | C | 15 | 16.6 | Coadd 1067 | 2025-10-06 20:22:48 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 45.5s) | C | 5 | 16.1 | 1068 | 2025-10-06 20:22:48 | MASTER- | (02h 41m 39.19s , -03d 46m 44.8s) | C | 5 | 15.9 | 1076 | 2025-10-06 20:22:57 | MASTER- | (02h 41m 39.18s , -03d 46m 45.2s) | C | 5 | 15.9 | 1076 | 2025-10-06 20:22:57 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 45.6s) | C | 5 | 16.1 | 1085 | 2025-10-06 20:23:06 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 45.8s) | C | 5 | 16.1 | 1090 | 2025-10-06 20:23:06 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 45.8s) | C | 15 | 16.6 | Coadd 1085 | 2025-10-06 20:23:06 | MASTER- | (02h 41m 39.20s , -03d 46m 45.4s) | C | 5 | 15.9 | 1094 | 2025-10-06 20:23:14 | MASTER- | (02h 41m 39.19s , -03d 46m 45.8s) | C | 5 | 15.9 | 1094 | 2025-10-06 20:23:14 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 46.2s) | C | 5 | 16.0 | 1102 | 2025-10-06 20:23:23 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 46.5s) | C | 5 | 16.1 | 1102 | 2025-10-06 20:23:23 | MASTER- | (02h 41m 39.18s , -03d 46m 46.1s) | C | 5 | 15.9 | 1111 | 2025-10-06 20:23:31 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 46.6s) | C | 5 | 16.1 | 1116 | 2025-10-06 20:23:31 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 46.6s) | C | 15 | 16.6 | Coadd 1111 | 2025-10-06 20:23:31 | MASTER- | (02h 41m 39.18s , -03d 46m 46.1s) | C | 5 | 16.0 | 1119 | 2025-10-06 20:23:40 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 46.7s) | C | 5 | 16.1 | 1120 | 2025-10-06 20:23:40 | MASTER- | (02h 41m 39.19s , -03d 46m 46.4s) | C | 5 | 15.9 | 1128 | 2025-10-06 20:23:48 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 46.9s) | C | 5 | 16.1 | 1128 | 2025-10-06 20:23:48 | MASTER- | (02h 41m 39.19s , -03d 46m 46.6s) | C | 5 | 15.9 | 1136 | 2025-10-06 20:23:57 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 47.1s) | C | 5 | 16.1 | 1141 | 2025-10-06 20:23:57 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 47.1s) | C | 15 | 16.6 | Coadd 1136 | 2025-10-06 20:23:57 | MASTER- | (02h 41m 39.18s , -03d 46m 46.7s) | C | 5 | 15.9 | 1145 | 2025-10-06 20:24:05 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 47.4s) | C | 5 | 16.1 | 1145 | 2025-10-06 20:24:05 | MASTER- | (02h 41m 39.18s , -03d 46m 46.9s) | C | 5 | 16.0 | 1207 | 2025-10-06 20:24:10 | MASTER-Kislovodsk | (02h 39m 44.60s , -03d 40m 18.3s) | P- | 120 | 14.3 | 1207 | 2025-10-06 20:24:10 | MASTER-Kislovodsk | (02h 39m 55.41s , -04d 03m 34.1s) | P| | 120 | 13.7 | 1160 | 2025-10-06 20:24:20 | MASTER- | (02h 41m 39.19s , -03d 46m 47.2s) | C | 5 | 15.9 | 1160 | 2025-10-06 20:24:20 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 47.7s) | C | 5 | 16.1 | 1168 | 2025-10-06 20:24:29 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 47.9s) | C | 5 | 16.1 | 1168 | 2025-10-06 20:24:29 | MASTER- | (02h 41m 39.19s , -03d 46m 47.4s) | C | 5 | 15.9 | 1177 | 2025-10-06 20:24:37 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 48.1s) | C | 5 | 16.1 | 1177 | 2025-10-06 20:24:37 | MASTER- | (02h 41m 39.20s , -03d 46m 47.7s) | C | 5 | 15.8 | 1185 | 2025-10-06 20:24:46 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 48.5s) | C | 5 | 16.2 | 1185 | 2025-10-06 20:24:46 | MASTER- | (02h 41m 39.19s , -03d 46m 48.0s) | C | 5 | 15.9 | 1194 | 2025-10-06 20:24:54 | MASTER-Tunka | (02h 42m 02.25s , -03d 51m 48.6s) | C | 5 | 16.2 | 1194 | 2025-10-06 20:24:54 | MASTER- | (02h 41m 39.20s , -03d 46m 48.2s) | C | 5 | 15.9 | 1203 | 2025-10-06 20:25:03 | MASTER- | (02h 41m 39.21s , -03d 46m 48.2s) | C | 5 | 15.9 | 1203 | 2025-10-06 20:25:03 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 48.7s) | C | 5 | 16.1 | 1214 | 2025-10-06 20:25:14 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 49.0s) | C | 5 | 16.1 | 1214 | 2025-10-06 20:25:14 | MASTER- | (02h 41m 39.20s , -03d 46m 48.7s) | C | 5 | 16.0 | 1222 | 2025-10-06 20:25:23 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 49.3s) | C | 5 | 16.2 | 1222 | 2025-10-06 20:25:23 | MASTER- | (02h 41m 39.21s , -03d 46m 49.0s) | C | 5 | 15.9 | 1231 | 2025-10-06 20:25:31 | MASTER-Tunka | (02h 42m 02.27s , -03d 51m 49.8s) | C | 5 | 16.1 | 1231 | 2025-10-06 20:25:31 | MASTER- | (02h 41m 39.21s , -03d 46m 49.3s) | C | 5 | 15.9 | 1270 | 2025-10-06 20:26:10 | MASTER-Tunka | (02h 42m 02.26s , -03d 51m 50.6s) | C | 5 | 16.1 | 1270 | 2025-10-06 20:26:10 | MASTER- | (02h 41m 39.20s , -03d 46m 50.5s) | C | 5 | 16.0 | 1347 | 2025-10-06 20:26:30 | MASTER-Kislovodsk | (02h 39m 44.69s , -03d 40m 13.3s) | P- | 120 | 14.3 | 1347 | 2025-10-06 20:26:30 | MASTER-Kislovodsk | (02h 39m 55.49s , -04d 03m 29.7s) | P| | 120 | 13.7 | 1487 | 2025-10-06 20:28:50 | MASTER-Kislovodsk | (02h 39m 44.76s , -03d 40m 09.2s) | P- | 120 | 14.3 | 1487 | 2025-10-06 20:28:50 | MASTER-Kislovodsk | (02h 39m 55.53s , -04d 03m 26.9s) | P| | 120 | 13.8 | 1626 | 2025-10-06 20:31:10 | MASTER-Kislovodsk | (02h 39m 44.78s , -03d 40m 03.9s) | P- | 120 | 14.3 | 1626 | 2025-10-06 20:31:10 | MASTER-Kislovodsk | (02h 39m 55.58s , -04d 03m 23.2s) | P| | 120 | 13.5 | 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/42133. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40201] GRB 251006B: BALROG localization (Fermi Trigger 781473909 / GRB 251006837)
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42132 SUBJECT: GRB 251006B: BALROG localization (Fermi Trigger 781473909 / GRB 251006837) DATE: 25/10/06 20:36:55 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 781473909 at 20:05:04 on 06 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) = 41.9 deg Decl.(2000.0) = -6.8 deg The 1 sigma statistical error radius is 3.4 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB251006837/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB251006837/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB251006837/json View this GCN Circular online at https://gcn.nasa.gov/circulars/42132. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40200] GRB 251006B: Fermi GBM Final Real-time Localization
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42131 SUBJECT: GRB 251006B: Fermi GBM Final Real-time Localization DATE: 25/10/06 20:15:37 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 20:05:04 UT on 6 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251006B (trigger 781473909.040226 / 251006837). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 40.5, Dec = -4.0 (J2000 degrees, equivalent to J2000 02h 42m, -4d 00'), with a statistical uncertainty of 1.2 degrees. The angle from the Fermi LAT boresight is 105.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006837/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006837/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251006837/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42131. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40199] GRB 251005C: VLT/X-shooter Imaging
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42127 SUBJECT: GRB 251005C: VLT/X-shooter Imaging 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 40198] GRB 251006A (short): Glowbug gamma-ray detection
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42130 SUBJECT: GRB 251006A (short): Glowbug gamma-ray detection DATE: 25/10/06 20:09:57 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251006A, which was also detected by Fermi/GBM (GCN 42124). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-06 13:27:33.944 with a duration of 0.26 s and a total significance of about 18.8 sigma. The light curve comprises a single peak with possible substructure. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was recently removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42130. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40197] GRB 251005C: COLIBRÍ optical observations
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42129 SUBJECT: GRB 251005C: COLIBRÍ optical observations DATE: 25/10/06 18:58:06 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), Francis Fortin (IRAP), Jean-Luc Atteia (IRAP), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM): We imaged the field of the Swift GRB 251005C (Page et al., GCN Circ. 42113) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-06 11:23 to 12:30 UTC (from 19.28 to 20.40 hours after the trigger) and obtained 38 minutes of simultaneous exposure in the i and z filters. The data were reduced and coadded with the tenue software and analyzed 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. At the position of the XRT source reported by Goad et al. (GCN Circ. 42116) and at the position of the VT optical source reported by Palmerio et al. (GCN Circ. 42123), we do not detect any sources above our 3-sigma limits of i > 23.8 z > 23.3 However, at the position of the VT source there are hints of the presence of a faint resolved object at lower significance. Our results are consistent with the X-shooter photometry reported by Yadav et al. (GCN Circ. 42127). We caution that the apparent fading in the i band with respect to the earlier VT_R detection is not conclusive, as the VT_R band above 650 nm includes both i and z, and our limit in z alone is not much deeper than the original detection. 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/42129. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40196] Fermi GRB 251006A: Global MASTER-Net observations report
by GCN Circulars 06 Oct '25

06 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42128 SUBJECT: Fermi GRB 251006A: Global MASTER-Net observations report DATE: 25/10/06 18:45:52 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 251006A ( Fermi GBM team, GCN 42124) errorbox 16713 sec after notice time and 16748 sec after trigger time at 2025-10-06 18:06:43 UT, with upper limit up to 17.0 mag. The observations began at zenith distance = 42 deg. The sun altitude is -18.0 deg. The galactic latitude b = 4 deg., longitude l = 12 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3008484 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 16778 | 2025-10-06 18:06:43 | MASTER-SAAO | (17h 34m 02.34s , -16d 58m 33.7s) | C | 60 | 16.7 | 16778 | 2025-10-06 18:06:43 | MASTER-SAAO | (17h 32m 04.73s , -16d 43m 22.6s) | C | 60 | 16.8 | 16871 | 2025-10-06 18:08:16 | MASTER-SAAO | (17h 40m 13.62s , -14d 06m 21.6s) | C | 60 | 16.9 | 16871 | 2025-10-06 18:08:16 | MASTER-SAAO | (17h 38m 17.54s , -13d 51m 10.9s) | C | 60 | 17.0 | 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/42128. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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[vsnet-grb-info 40185] Swift GRB 251005A: Global MASTER-Net observations report
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42117 SUBJECT: Swift GRB 251005A: Global MASTER-Net observations report DATE: 25/10/05 22:14:35 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 251005A ( K. L. Page et al., GCN 42113) errorbox 21439 sec after notice time and 21469 sec after trigger time at 2025-10-05 22:04:43 UT, with upper limit up to 16.8 mag. The observations began at zenith distance = 82 deg. The sun altitude is -52.7 deg. The galactic latitude b = -14 deg., longitude l = 185 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3007783 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 21560 | MASTER-SAAO | C | 180 | 16.8 | 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/42117. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40184] GRB 251005C: GOTO optical upper limits
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42115 SUBJECT: GRB 251005C: GOTO optical upper limits DATE: 25/10/05 18:48:41 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> B. P. Gompertz, D. O’Neill, G. Ramsay, P. O’Brien, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, A. Kumar, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, 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 251005C (Page et al., GCN 42113). A targeted observation was performed at 17:48:32 (1.7 hours after trigger), consisting 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 find no new optical sources consistent with the Swift/XRT localisation (Goad et al., GCN 42116) to a 3-sigma limiting AB magnitude of L > 19.65 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/42115. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40183] GRB 251005C: Swift detection of a burst
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42113 SUBJECT: GRB 251005C: Swift detection of a burst DATE: 25/10/05 16:23:27 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K. L. Page (U Leicester), S. Dichiara (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL) and M. J. Moss (GSFC) report on behalf of the Neil Gehrels Swift Observatory Team: At 16:06:53 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251005C (trigger=1401726). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 75.673, +16.882 which is RA(J2000) = 05h 02m 42s Dec(J2000) = +16d 52' 54" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a double-peaked structure with a duration of about 2 sec. The peak count rate was ~4,500 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 16:08:52.2 UT, 118.3 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 75.68331, 16.88007 which is equivalent to: RA(J2000) = 05h 02m 44.00s Dec(J2000) = +16d 52' 48.3" with an uncertainty of 2.1 arcseconds (radius, 90% containment). This location is 36 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 in excess of the Galactic value (3.19 x 10^21 cm^-2, Willingale et al. 2013), with an excess column of 5 (+3.76/-3.16) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 122 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 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 0.461. Burst Advocate for this burst is K. L. Page (klp5 AT leicester.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/42113. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40182] GRB 251005C: Enhanced Swift-XRT position
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42116 SUBJECT: GRB 251005C: Enhanced Swift-XRT position DATE: 25/10/05 19:33:09 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 1541 s of XRT Photon Counting mode data and 2 UVOT images for GRB 251005C, 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 = 75.68325, +16.88054 which is equivalent to: RA (J2000): 05h 02m 43.98s Dec (J2000): +16d 52' 49.9" with an uncertainty of 2.3 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/42116. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40180] Fermi trigger No 781367244: Global MASTER-Net observations report
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42114 SUBJECT: Fermi trigger No 781367244: Global MASTER-Net observations report DATE: 25/10/05 18:15:34 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB251005.60 (trigger No 781367244,19h 54m 28.80s , -08d 55m 12.0s, R=6.5) errorbox 11063 sec after notice time and 11097 sec after trigger time at 2025-10-05 17:32:16 UT, with upper limit up to 17.8 mag. Observations started at twilight. The observations began at zenith distance = 23 deg. The sun altitude is -11.1 deg. The galactic latitude b = -19 deg., longitude l = 32 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3007732 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 11127 | 2025-10-05 17:32:16 | MASTER-SAAO | (19h 53m 05.61s , -08d 35m 40.3s) | C | 60 | 17.2 | 11127 | 2025-10-05 17:32:16 | MASTER-SAAO | (19h 51m 12.16s , -08d 20m 30.0s) | C | 60 | 17.6 | 11226 | 2025-10-05 17:33:55 | MASTER-SAAO | (20h 01m 01.07s , -08d 37m 00.8s) | C | 60 | 17.4 | 11226 | 2025-10-05 17:33:55 | MASTER-SAAO | (19h 59m 07.53s , -08d 21m 50.9s) | C | 60 | 17.8 | 11424 | 2025-10-05 17:37:13 | MASTER-SAAO | (19h 44m 10.05s , -10d 29m 55.4s) | C | 60 | 17.5 | 11424 | 2025-10-05 17:37:13 | MASTER-SAAO | (19h 42m 15.83s , -10d 14m 44.1s) | C | 60 | 17.8 | 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/42114. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40181] GRB 251002A: Mondy/AZT-33IK optical observations
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42110 SUBJECT: GRB 251002A: Mondy/AZT-33IK optical observations DATE: 25/10/05 07:05:17 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of GRB 251002A detected by SVOM (Saccardi et. al, GCN 42060) in the R-filter with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy). The observations began on 2025-10-03 17:00 UT, i.e. ~0.88 days since trigger and consisted of 30x120 s exposures. The optical source found by SVOM (Palmerio et. al, GCN 42061) at z = 2.178 (Saccardi et. al, GCN 42076) and also observed by (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) is detected in the co-add image of 30x120 s. Preliminary photometry and observation details are presented below: Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (nxs) (3sigma) 2025-10-03 17:00:32 0.88586 30x120 R 20.96 0.12 22.0 The photometry was calibrated using reference stars from (Moskvitin et. al, GCN 42065) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42110. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40179] Swift/BAT trigger 1401726: GOTO optical upper limits
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42115 SUBJECT: Swift/BAT trigger 1401726: GOTO optical upper limits DATE: 25/10/05 18:48:41 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> B. P. Gompertz, D. O’Neill, G. Ramsay, P. O’Brien, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, A. Kumar, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, 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 Swift/BAT trigger 1401726. The current difficulties with the distribution of GCN circulars means we are unsure of the official designation of this burst at the time of submission. A targeted observation was performed at 17:48:32 (1.7 hours after trigger), consisting 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 find no new optical sources consistent with the Swift/XRT localisation to a 3-sigma limiting AB magnitude of L > 19.65 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/42115. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40177] GRB 251002A: Insight-HXMT detection
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42109 SUBJECT: GRB 251002A: Insight-HXMT detection DATE: 25/10/05 06:33:10 GMT FROM: xueyuan zao <zaoxueyuan(a)gmail.com> Xue-Yuan Zao, Zheng-Hang Yu, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-10-02T20:14:52.800 (T0), Insight-HXMT/HE detected a long burst GRB 251002A, which is also detected by Fermi/GBM (Jacob Smith et al., GCN #42093) and SVOM/ECLAIRs (A. Saccardi et al., GCN #42060). The Insight-HXMT/HE light curve mainly consists of multiple pulses with a T90 of 13.8 +2.3/-3.1 s. The 1s peak rate, measured from T0+6.050 s, is 1080 cnts/sec. The total counts from this burst is 4528 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251002A.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 30-1000 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/42109. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40176] GRB 251005A: Fermi GBM Final Real-time Localization
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42112 SUBJECT: GRB 251005A: Fermi GBM Final Real-time Localization DATE: 25/10/05 14:37:49 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 14:27:19 UT on 5 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251005A (trigger 781367244.128264 / 251005602). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 298.6, Dec = -8.9 (J2000 degrees, equivalent to J2000 19h 54m, -8d 54'), with a statistical uncertainty of 6.5 degrees. The angle from the Fermi LAT boresight is 104.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251005602/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251005602/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251005602/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42112. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40178] GRB 251005A: Fermi GBM Final Localization
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42111 SUBJECT: GRB 251005A: Fermi GBM Final Localization DATE: 25/10/05 09:53:14 GMT FROM: Utkarsh Pathak at IIT Bombay <utkarshpathak.07(a)gmail.com> The Fermi GBM team reports the detection of a likely LONG GRB "At 05:27:08.25 UT on 05 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251005A (trigger 781334833/251005227). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 227.84, Dec = 5.07 (J2000 degrees, equivalent to J2000 15h 11m, 5d 04'), with a statistical uncertainty of 4.90 degrees. The angle from the Fermi LAT boresight is 86 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251005227/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251005227/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251005227/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/42111. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40175] GRB 251002A: Insight-HXMT detection
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42108 SUBJECT: GRB 251002A: Insight-HXMT detection DATE: 25/10/05 05:30:19 GMT FROM: xueyuan zao <zaoxueyuan(a)gmail.com> Xue-Yuan Zao, Zheng-Hang Yu, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-10-02T20:14:52.800 (T0), Insight-HXMT/HE detected a long burst GRB 251002A, which is also detected by Fermi/GBM (Jacob Smith et al., GCN #42093) and SVOM/ECLAIRs (A. Saccardi et al., GCN #42060). The Insight-HXMT/HE light curve mainly consists of multiple pulses with a T90 of 13.8 +2.3/-3.1 s. The 1s peak rate, measured from T0+6.050 s, is 1080 cnts/sec. The total counts from this burst is 4528 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251002A.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 30-1000 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/42108. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40174] GRB 251005A: Swift detection of a burst
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42113 SUBJECT: GRB 251005A: Swift detection of a burst DATE: 25/10/05 16:23:27 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K. L. Page (U Leicester), S. Dichiara (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL) and M. J. Moss (GSFC) report on behalf of the Neil Gehrels Swift Observatory Team: At 16:06:53 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251005A (trigger=1401726). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 75.673, +16.882 which is RA(J2000) = 05h 02m 42s Dec(J2000) = +16d 52' 54" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a double-peaked structure with a duration of about 2 sec. The peak count rate was ~4,500 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 16:08:52.2 UT, 118.3 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 75.68331, 16.88007 which is equivalent to: RA(J2000) = 05h 02m 44.00s Dec(J2000) = +16d 52' 48.3" with an uncertainty of 2.1 arcseconds (radius, 90% containment). This location is 36 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 in excess of the Galactic value (3.19 x 10^21 cm^-2, Willingale et al. 2013), with an excess column of 5 (+3.76/-3.16) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 122 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 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 0.461. Burst Advocate for this burst is K. L. Page (klp5 AT leicester.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/42113. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40173] EP251003a: Einstein Probe detection of an X-ray transient
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42107 SUBJECT: EP251003a: Einstein Probe detection of an X-ray transient DATE: 25/10/05 03:22:32 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. C. Liu (THU), Y. Q. Zhao (USTC), C. Zhou (HUST), H. W. Pan (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 EP251003a. The WXT position of the source is R.A. = 56.934 deg, DEC = -10.929 deg (J2000) with an uncertainty of 2.549 arcmin in radius (90% C.L. statistical and systematic). The transient was first detected by WXT in an observation that started at 2025-10-03T18:11:50 (UTC). The 0.5-4 keV spectrum can be fitted with an absorbed powerlaw model with hydrogen column density of 0.4(+3.2, -0.4)x10^21 cm^-2 and a photon index of 0.9(+1.1, -0.5). The average unabsorbed 0.5-4 keV flux is 3.8(+1.4, -1.1) x 10^-11 erg/s/cm^2. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed. An uncatalogued X-ray source was detected at R.A. = 56.9218 deg, DEC = -10.9321 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The 0.5-10 keV spectrum can be fitted with an absorbed powerlaw model with hydrogen column density of 0.0 (+1.7, -0.0)x10^21 cm^-2 and a photon index of 1.7(+0.6, -0.2). The average unabsorbed 0.5-10 keV flux is 8.3(+1.6, -1.9) x 10^-13 erg/s/cm^2. All the uncertainties of the parameters are 90% C.L. statistical. Further follow-up observations are encouraged. 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/42107. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40172] GRB 251005B: Fermi GBM Final Real-time Localization
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42112 SUBJECT: GRB 251005B: Fermi GBM Final Real-time Localization DATE: 25/10/05 14:37:49 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 14:27:19 UT on 5 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251005B (trigger 781367244.128264 / 251005602). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 298.6, Dec = -8.9 (J2000 degrees, equivalent to J2000 19h 54m, -8d 54'), with a statistical uncertainty of 6.5 degrees. The angle from the Fermi LAT boresight is 104.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251005602/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251005602/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251005602/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42112. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40171] GRB 251002A: NIR observations with WINTER
by GCN Circulars 05 Oct '25

05 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42105 SUBJECT: GRB 251002A: NIR observations with WINTER DATE: 25/10/04 04:03:05 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (Caltech), Viraj Karambelkar (Columbia/CCA), Benjamin Schneider (LAM), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 251002A (Saccardi et al., GCN 42060; Sun et al., GCN 42075; Kenya et al., GCN 42084; Smith et al., GCN 42093) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2025-10-03T03:49:03 UTC in the J band (~7.6 hours after the GRB trigger), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) We do not detect a source at the optical counterpart location (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; Senik et al., GCN 42067; 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 et al., GCN 42099; Calapai et al., GCN 42101). We obtain the following 5-sigma upper limit: J ~ 19.2 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/42105. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40170] GRB 251003A: Swift/UVOT Upper Limits
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42100 SUBJECT: GRB 251003A: Swift/UVOT Upper Limits DATE: 25/10/03 18:33:33 GMT FROM: s.shilling(a)lancaster.ac.uk S. P. R. Shilling (Lancaster U.), M. De Pasquale (Univ. Messina) and A. P. Beardmore (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251003A 79 s after the BAT trigger (Beardmore et al., GCN Circ. 42070). No optical afterglow consistent with the enhanced XRT position (Evans et al., GCN Circ. 42088) or those reported by other instruments (Aceituno et al., GCN Circ. 42072; Moreno Méndez et al., GCN Circ. 42073; Strausbaugh et al., GCN Circ. 42074; Worssam et al., GCN Circ. 42094), 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 79 229 147 >20.70 u 291 474 180 >19.78 v 33828 34558 711 >20.01 b 43530 43837 298 >20.30 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.408 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42100. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40169] GRB 251002A: Swift/UVOT detection
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42099 SUBJECT: GRB 251002A: Swift/UVOT detection DATE: 25/10/03 18:26:26 GMT FROM: s.shilling(a)lancaster.ac.uk S.P.R. Shilling (Lancaster U.) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251002A in the U band for a total of 1.5 ks, starting 3.6 ks after the SVOM/ECLAIRs trigger (Saccardi et al., GCN Circ. 42060). A source is detected in the U band at a position that is consistent with other detections by other instruments in the optical (Palmerio et al., GCN 42061; Turpin et al., GCN 42062; Jelinek et al., GCN 42063; Julia-Maroto et al., GCN 42064; Moskvitin et al., GCN 42065; Perez-Garcia et al., GCN 42606; Senik et al., GCN 42067; 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). Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the stacked U band images are: Filter T_start(s) T_stop(s) Exp(s) Mag U 3628 9263 1476 19.02 +/- 0.08 The magnitude reported here is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42099. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40168] GRB 251001A: AstroSat CZTI detection
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42098 SUBJECT: GRB 251001A: AstroSat CZTI detection DATE: 25/10/03 18:19:12 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (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 GRB 251001A which was also detected by Fermi/GBM (GCN Circ. 41993), Insight-HXMT (Wang et al., 42057). We detect only the second pulse as seen in the GBM lightcurve because the source is likely at a sky position where our effective area is low. The source was detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-10-01 02:40:59.96 UTC. The measured peak count rate associated with the burst is 372 (+65, -75) counts/s above the background in the combined data of all four quadrants, with a total of 333 (+172, -206) counts. The local mean background count rate was 1380 (+11, -11) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a 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/42098. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40167] GRB 251001B: COLIBRÍ further observations and evidence of a multi-wavelength shallow decay
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42097 SUBJECT: GRB 251001B: COLIBRÍ further observations and evidence of a multi-wavelength shallow decay DATE: 25/10/03 17:59:09 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Benjamin Schneider (LAM), Camila Angulo (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (OCA), 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), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM): We reobserved the field of the GRB 251001B (Fermi GBM team, GCN Circ. 42038; Beardmore et al. GCN Circ. 42039) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-03 12:00 to 12:19 UTC (from 45.7 to 46.0 hours after the trigger) and obtained 16 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with custom 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. We detected the optical counterpart previously reported by Gompertz et al. (GCN Circ. 42040), An et al. (GCN Circ. 42041), Strausbaugh & Cucchiara (GCN Circ. 42043), O'Neill et al. (GCN Circ. 42046), de Ugarte Postigo et al. (GCN Circ. 42050), Ma et al. (GCN Circ. 42051), Sanchez-Ramirez et al. (GCN Circ. 42053), Schneider et al. (GCN Circ. 42054), and Breeveld et al. (GCN Circ. 42055) at preliminary magnitudes of: r = 22.28 +/- 0.14. z = 22.08 +/- 0.41 (with a 3-sigma detection limit of z = 21.85). By comparing the optical data reported by the aforementioned facilities and COLIBRÍ, we estimate a spectral index of approximately -0.5. This shallow decay is consistent with the temporal evolution observed in the X-ray band after 10ks from the trigger (https://www.swift.ac.uk/xrt_curves/01400467/) Further observations are planned. 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/42097. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40166] GRB 251003A: Swift-XRT refined Analysis
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42096 SUBJECT: GRB 251003A: Swift-XRT refined Analysis DATE: 25/10/03 16:16:36 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-OAR), S. Lanava (PSU), S. Dichiara (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.8 ks of XRT data for GRB 251003A, from 59 s to 34.6 ks after the trigger. The data comprise 126 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+4.6 ks) can be modelled with a power-law decay with a decay index of alpha=0.6 (+0.4, -0.3). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.67 (+0.11, -0.10). The best-fitting absorption column is 1.4 (+3.0, -1.4) x 10^22 cm^-2, at a redshift of 4.412, in addition to the Galactic value of 4.4 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 2.8 x 10^-11 (7.5 x 10^-11) erg cm^-2 count^-1. A summary of the WT-mode spectrum is thus: Galactic foreground: 4.4 x 10^21 cm^-2 Intrinsic column: 1.4 (+3.0, -1.4) x 10^22 cm^-2 at z=4.412 Photon index: 2.67 (+0.11, -0.10) If the light curve continues to decay with a power-law decay index of 0.6, the count rate at T+24 hours will be 8.2 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 x 10^-13 (6.1 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01400964. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42096. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40165] GRB 251003A: COLIBRÍ photometric redshift
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42095 SUBJECT: GRB 251003A: COLIBRÍ photometric redshift DATE: 25/10/03 15:49:16 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Ny Avo Rakotondrainibe (LAM), Enrique Moreno Méndez (UNAM), Antonio de Ugarte Postigo (LAM), Camila Angulo (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), 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), Francesco Magnani (CPPM), Margarita Pereyra (UNAM) and Fredd Sánchez Álvarez (UNAM): COLIBRÍ performed additional observations of the Fermi and Swift GRB 251003A (Fermi GBM team, GCN Circ. 42069; Beardmore et al., GCN Circ. 42070) starting from 2025-10-03 04:04:59 (2.1 hr after the trigger) and obtained images in the g, i, y filters. The photometry of the afterglow (Aceituno et al. GCN Circ. 42072; Moreno Méndez et al. GCN Circ. 42073; Strausbaugh et al. GCN Circ. 42074; Freeberg et al. GCN Circ. 42085; Worssam et al., GCN Circ. 42094) was performed using STDWeb/STDPipe (Karpov 2025), was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. After combining data obtained from Moreno Méndez et al., GCN Circ. 42073 and correcting for the Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.36 mag (Schlafly & Finkbeiner 2011), we fit a power-law model to the grizy-bands using the SMC extinction curve and we derive a photometric redshift of z = 4.38+0.07-0.04 (1-sigma c.l., statistical errors only). Our result is consistent with the GTC/OSIRIS+ redshift of z = 4.41 (Sanchez-Ramirez et al., GCN Circular 42086). 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/42095. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40164] GRB 251003A: GOTO detection of the optical counterpart
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42094 SUBJECT: GRB 251003A: GOTO detection of the optical counterpart DATE: 25/10/03 14:27:54 GMT FROM: I. Worssam at University of Birmingham <ixw352(a)student.bham.ac.uk> I. Worssam, B. P. Gompertz, D. O’Neill, M. E. Wortley, G. Ramsay, R. Starling, M. Kennedy, B. Godson, J. Lyman, K. Ackley, M. J. Dyer, K. Ulaczyk, A. Kumar,, 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 251003A (Fermi GBM team, GCN 42069; Beardmore et al. GCN 42070). Targeted observations were performed at 2025-10-03 02:03:05 (4.57mins post trigger) and 2025-10-03 03:11:32 (1.22h post trigger). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). We detect the optical counterpart (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) with measured AB magnitudes of L = 19.94 ± 0.24 and L = 20.83 ± 0.28 for the two epochs respectively. 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/42094. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40163] GRB 251002A: Fermi GBM Observation
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42093 SUBJECT: GRB 251002A: Fermi GBM Observation DATE: 25/10/03 14:21:41 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> Jacob Smith (UAH), O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 20:14:51.01 UT on 02 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251002A (trigger 781128896/251002844). which was also detected by SVOM/ECLAIRs (A. Saccardi et al. 2025, GCN 42060). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position. VLT/X-shooter detected a spectroscopic redshift of z = 2.178 (A. Saccardi et al. 2025, GCN 42076). The angle from the Fermi LAT boresight is 53 degrees. The GBM light curve multiple emission episodes with a duration (T90) of about 26 s (50-300 keV). The time-averaged spectrum from T0-6.9 to T0+14.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.88 +/- 0.07 and the cutoff energy, parameterized as Epeak, is 180 +/- 10 keV. The event fluence (10-1000 keV) in this time interval is (4.6 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+7.9 s in the 10-1000 keV band is 7.1 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 140 +/- 20 keV, alpha = -0.7 +/- 0.1 and beta = -2.2 +/- 0.1. 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/42093. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40162] LIGO/Virgo/KAGRA S251003at: Retraction of GW compact binary merger candidate
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42092 SUBJECT: LIGO/Virgo/KAGRA S251003at: Retraction of GW compact binary merger candidate DATE: 25/10/03 13:58:15 GMT FROM: Dounia Nanadoumgar Lacroze at IFAE Barcelona <dnala(a)ifae.es> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: The trigger S251003at is no longer considered to be a candidate of interest. This candidate was initially identified by one or more early-warning analyses by matching partial signal templates to the data. Analysis of additional data up to the putative merger time, with full signal templates, did not make a significant detection, indicating that the initial candidate was likely due to transient noise. View this GCN Circular online at https://gcn.nasa.gov/circulars/42092. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40161] GRB 251002A: GOTO detection of optical counterpart
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42091 SUBJECT: GRB 251002A: GOTO detection of optical counterpart DATE: 25/10/03 13:45:47 GMT FROM: MEW020(a)student.bham.ac.uk M. E. Wortley, B. P. Gompertz, D. O’Neill, G. Ramsay, R. Starling, M. Kennedy, B. Godson, J. Lyman, K. Ackley, M. J. Dyer, K. Ulaczyk, A. Kumar,, 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) that serendipitously covered the field of GRB 251002A (Saccardi et al., GCN 42060) during survey operations. We detect the optical counterpart (Palmerio et al., GCN 42061; Turpin et al., GCN 42062; Jelinek et al., GCN 42063; Julia-Maroto et al., GCN 42064; Moskvitin et al., GCN 42065; Perez-Garcia et al., GCN 42606; Senik et al., GCN 42067; 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; Kennea et al., GCN 42084; Odeh et al., GCN 42087) in GOTO L-band (400-700 nm) imaging taken at 2025-10-03 01:03:06 UT (4.80h post-trigger) consisting of 4x45s exposures. The measured AB magnitude is L = 19.87 ± 0.31. 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/42091. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40160] GRB 251001C: SVOM/GRM observation
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42090 SUBJECT: GRB 251001C: SVOM/GRM observation DATE: 25/10/03 13:40:21 GMT FROM: yzh807926(a)163.com SVOM/GRM team: Zheng-Hang Yu, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Piron (LUPM), Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 251001C (SVOM trigger reference: sb25100106) at 2025-10-01T15:07:27.000 UTC (T0), which is also detected by Glowbug gamma-ray telescope (C.C. Cheung et al. 2025, GCN#42049). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists mainly of a single pulse with a T90 of 11.7 +4.5/-4.1 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251001C.png In addition, the position of this burst, as determined by Glowbug gamma-ray telescope (RA= 82.7, DEC= 21.9, GCN#42049), is located at about 59.47 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-3 to T0+15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.24 +0.19/-0.22 and the cutoff energy, parameterized as Epeak, is 301 +314/-97 keV. The event fluence (10-1000 keV) in this time interval is (3.46 +0.53/-0.50)E-06 erg/cm^2. The localization of GRB 251001C in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251001C_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: Zheng-Hang Yu(IHEP)(zhyu(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42090. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40159] EP250821a: iTelescope T-59 possible detection of the optical counterpart
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42089 SUBJECT: EP250821a: iTelescope T-59 possible detection of the optical counterpart DATE: 25/10/03 12:59:37 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 EP250821a detected by the Einstein Probe (EP) (Hu et al., GCN Circ. 41459) with the iTelescope.Net (http://www.itelescope.net) T59 (Planewave 20" CDK) telescope located at the Siding Spring Observatory, Australia. We took nine images of 120-second exposures in the Red filter starting from August 21 at 10:25:34 (UT), about 3 hours after the trigger, and stopped at 12:48:14 (UT). Please note that there were no observations between 10:33 and 11:30, and between 11:39 and 12:41 due to our scheduling error. We have a weak detection of the optical counterpart (Dichiara et al., GCN Circ. 41469; Li et al., GCN Circ. 41470; Yao et al., GCN Circ. 41485) in the stacked image of the first three exposures from 10:25:34 to 10:32:47 UT. The estimated magnitude is ~18.5. No optical counterpart was detected in the following six images collected between 11:30:00 and 12:48:14 (UT). The 5-sigma upper limit of the stacked image of the last six images is 17.5 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/42089. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40158] GRB 251003A: Enhanced Swift-XRT position
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42088 SUBJECT: GRB 251003A: Enhanced Swift-XRT position DATE: 25/10/03 11:31:53 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 1392 s of XRT Photon Counting mode data and 4 UVOT images for GRB 251003A, 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 = 18.52924, +56.49080 which is equivalent to: RA (J2000): 01h 14m 07.02s Dec (J2000): +56d 29' 26.9" 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/42088. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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