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

[vsnet-grb-info 40054] GRB 250924A: Swift-BAT refined analysis
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41987 SUBJECT: GRB 250924A: Swift-BAT refined analysis DATE: 25/09/25 19:39:17 GMT FROM: Hans Krimm at NSF/NASA-GSFC <hkrimm(a)nsf.gov> D. Sadaula (GSFC/UMBC), 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), T. Sakamoto (AGU), M. H. Siegel (PSU), (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250924A(trigger #1351790) (Siegel, et al., GCN Circ. 41959). The BAT ground-calculated position is RA, Dec = 51.908, 74.665 deg, which is RA(J2000) = 03h 27m 37.8s Dec(J2000) = +74d 39' 55.1" with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment). The partial coding was 12%. The mask-weighted light curve shows a single broad pulse, extending from approximately T-10 to T+20 seconds. T90 (15-350 keV) is 26.53 +- 3.72 sec (estimated error including systematics). The time-averaged spectrum from T-9.92 to T+20.00 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.47 +- 0.17. The fluence in the 15-150 keV band is 2.5 +- 0.3 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+15.78 sec in the 15-150 keV band is 2.1 +- 0.7 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/1351790 View this GCN Circular online at https://gcn.nasa.gov/circulars/41987. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40053] GRB 250925A: GROWTH-India Telescope Upper Limits
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41986 SUBJECT: GRB 250925A: GROWTH-India Telescope Upper Limits DATE: 25/09/25 19:01:36 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> A.P. Saikia, S. Patil, Y. Wagh, T. Mohan, V. Swain, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of Swift GRB 250925A (Dichiara et al., GCN 41985), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-09-25 17:17:09 UT, i.e., 13 minutes after the GRB trigger. We obtained multiple exposures in g', r', and i' bands. We did not detect the source in our images within the Swift-BAT localization region. The photometric upper limits are as follow: | MJD (mid) | Filter | tmid-t0 (min) | Exposure Time (sec) | Upper limit (AB) | | ------------ | ------ | ------------ | ------------------- | ---------------- | | 60943.727303 | g' | 22.88 | 300 | 20.5 | | 60943.753831 | r' | 61.08 | 300 | 20.4 | | 60943.730914 | i' | 28.08 | 300 | 19.5 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/41986. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40052] GRB 250925A: Swift detection of a burst
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41985 SUBJECT: GRB 250925A: Swift detection of a burst DATE: 25/09/25 17:19:22 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> S. Dichiara (PSU), R. Gupta (NASA GSFC), N. J. Klingler (GSFC/UMBC/CRESSTII), S. Lanava (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 17:04:26 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250925A (trigger=1352124). Swift could not immediately slew to the burst due to an observing constraint. The BAT on-board calculated location is RA, Dec 341.201, +46.574 which is RA(J2000) = 22h 44m 48s Dec(J2000) = +46d 34' 25" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve is only available until T+8s, but this shows a complex peak of at least 20 s duration. The peak count rate was ~1400 counts/sec (15-350 keV), at ~1 sec after the trigger. Due to an observing constraint, Swift will not slew at this time. XRT and UVOT data will be obtained later. Burst Advocate for this burst is S. Dichiara (sbd5667 AT psu.edu) 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/41985. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40051] Swift GRB250925.71: Global MASTER-Net observations report
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41984 SUBJECT: Swift GRB250925.71: Global MASTER-Net observations report DATE: 25/09/25 17:14:34 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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the Swift GRB250925.71 (trigger No 1352124,22h 44m 48.24s , +46d 34m 26.4s, R=0.05) errorbox 16 sec after notice time and 59 sec after trigger time at 2025-09-25 17:05:26 UT, with upper limit up to 12.9 mag. The observations began at zenith distance = 16 deg. The sun altitude is -40.0 deg. The galactic latitude b = -11 deg., longitude l = 102 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2999810 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 65 | MASTER-Tunka | P- | 10 | 12.9 | 65 | MASTER- | C | 10 | 16.6 | 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/41984. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40050] GRB 250922A: SVOM/GRM observation
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41983 SUBJECT: GRB 250922A: SVOM/GRM observation DATE: 25/09/25 14:25:36 GMT FROM: tanwj(a)ihep.ac.cn SVOM/GRM team: Wen-Jun Tan, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Marius Brunet (IRAP) and Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 250922A (SVOM burst-id sb25092201) at 2025-09-22T03:07:21.000 (T0), which is also detected by FERMI/GBM (GBM team, GCN # 41933) With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 15.89 +10.74/-1.52s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250922A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 353.54, Dec = 0.42, GCN #41933), is located at about 50 degrees from the SVOM optical axis, which is just outside the ECLAIRs field of view. With this localization given by FERMI/GBM, the time-averaged spectrum from T0-5 to T0+15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.61 +0.22/-0.40 and the cutoff energy, parameterized as Epeak, is 473 +165/-99 keV. The event fluence (10-1000 keV) in this time interval is (2.03 +0.33/-0.31)E-06 erg/cm^2. The localization of GRB 250922A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb250922A_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: Wen-Jun Tan (IHEP)(tanwj(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41983. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40049] GRB 250924A: 1.6m Mephisto optical upper limits
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41982 SUBJECT: GRB 250924A: 1.6m Mephisto optical upper limits DATE: 25/09/25 11:07:51 GMT FROM: liuxk(a)ynu.edu.cn Helong Guo, Yichen Jin, Xingzhu Zou, Guowang Du, Xufeng Zhu, Brajesh Kumar, Xinlei Chen, Yuanpei Yang, Tao Wang, Xiangkun Liu and Xiaowei Liu (all SWIFAR, YNU) report on behalf of Mephisto Team: Simultaneous multi-band photometric observations of the GRB 250924A detected by Swift (Siegel et al., GCN 41959) was performed with 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were started from 16:00:12 2025-09-24 UT (~7.7 hr after the trigger) and six frames of 45 sec each were obtained in uvgr bands. The afterglow candidate (Becerra et. al., GCN 41960; Schneider et al., GCN 41963; Freeberg et. al., GCN 41968; Pankov et al., GCN 41969; Zhang & Filippenko, GCN 41970; Mo et al., GCN 41972, Siegel et al., GCN 41975, Ma et al., GCN 41976) is not detected in our uvgr stacked band images. The 3-sigma upper limit are listed below: ---------------------------------------------------------------------------- Start_Time(UT) Filter Exp (sec) LimMag(AB) 2025-09-24T16:00:15 u 45*6 >21.34 2025-09-24T16:06:46 v 45*6 >21.66 2025-09-24T16:00:12 g 45*6 >22.22 2025-09-24T16:06:43 r 45*6 >22.46 ---------------------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. ---------------------------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/41982. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40048] GRB 250924A: SAO RAS optical observations
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41981 SUBJECT: GRB 250924A: SAO RAS optical observations DATE: 25/09/25 10:53:27 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO), V. Goranskij (SAI MSU), N. Pankov (HSE), A. Pozanenko (IKI) report on behalf of GRB follow-up collaboration and IKI-GRB-FuN. We observed the field of the GRB 250924A (Siegel et. al, GCN 41897; Osborne et. al, GCN 41973; Campana et. al, GCN 41974) with two SAO RAS telescopes, 1-m Zeiss-1000 equipped with the CCD-photometer on September 24/25, 23:41:32--00:27:16, and 6-m BTA equipped with the focal reducer SCORPIO-2 (Afanasiev & Moiseev, 2011, BaltA, 20, 363) on September 25, 01:42:55--01:58:24 UT. The optical transient (Siegel et. al, GCN 41959; Becerra et. al, GCN 41960; Schneider et. al, GCN 41963; Freeberg et. al, GCN 41968; Pankov et. al, GCN 41969; Zheng and Filippenko, GCN 41970; Siegel, GCN 41975; Ma et al., GCN 41976; Cotter et al., GCN 41980; and also observed in NIR, Mo et. al, GCN 41972) is clearly detected in our stacked frames. Preliminary results are as following. Date UTstart Exptime t-T0 Filter OT Err. UL Tel. s (mid, days) (3sigma) 2025.09.24 23:41:32 2520 0.65689 Rc 23.18 +/- 0.24 23.5 1-m 2025.09.25 01:42:55 600 0.73068 Rc 23.07 +/- 0.10 24.3 6-m The photometry calibrated against nearby USNO-B1.0 stars (R2 magnitudes) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41981. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40047] GRB 250924A: NOT optical observations
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41980 SUBJECT: GRB 250924A: NOT optical observations DATE: 25/09/25 07:54:34 GMT FROM: Laura Cotter at University College Dublin <laura.cotter(a)ucdconnect.ie> L. Cotter (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. de Ugarte Postigo (LAM), B. Schneider (LAM), G. Corcoran (UCD), K. Valeckas (NOT and NBI), report on behalf of a larger collaboration: We observed the optical afterglow of GRB 250924A (Siegel et al., GCN 41959) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. A total of 3x300 s of imaging in the r band was acquired. At the mid epoch of 2025 Sep 25.117 UT (18.49 hr after the Swift/BAT trigger), we measure a magnitude of r = 23.55 +/- 0.15 (AB), calibrated against nearby objects from the Pan-STARRS catalog, and not corrected for Galactic extinction. Comparing our result to previous measurements (e.g. Pankov et al., GCN 41969), the afterglow is significantly fainter than the extrapolation using the decay rate observed at early times (Schneider et al., GCN 41963; Zhang & Filippenko, GCN 41970), indicating a steepening of the light curve. View this GCN Circular online at https://gcn.nasa.gov/circulars/41980. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40046] GRB 250924A: AstroSat CZTI detection
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41979 SUBJECT: GRB 250924A: AstroSat CZTI detection DATE: 25/09/25 06:29:43 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> M. Tembhurnikar (IUCAA), Harsha K. H. (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 a long-duration GRB 250924A which was also detected by Swift/BAT (Siegel et al., GCN Circ. 41959). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-09-24 08:18:32.00 UTC. The measured peak count rate associated with the burst is 48 (+17, -5) counts/s above the background in the combined data of three quadrants (out of four), with a total of 967 (+370, -133) counts. The local mean background count rate was 197 (+1, -3) counts/s. Using cumulative rates, we measure a T90 of 27 (+9, -5) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. 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/41979. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40045] GRB 250914A: AstroSat CZTI detection
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41978 SUBJECT: GRB 250914A: AstroSat CZTI detection DATE: 25/09/25 05:57:47 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> A. Arya (IITB), A. Goyal (IITB), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (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 a long-duration GRB 250914A which was also detected by Konus-Wind (GCN Notices). 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 2025-09-14 20:52:17.50 UTC. The measured peak count rate associated with the burst is 234 (+35, -27) counts/s above the background in the combined data of all quadrants, with a total of 2354 (+246, -269) counts. The local mean background count rate was 221 (+3, -4) counts/s. Using cumulative rates, we measure a T90 of 18 (+2, -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 single peak of emission with the strongest peak at 2025-09-14 20:52:17.33 UTC. The measured peak count rate associated with the burst is 457 (+75, -67) counts/s above the background in the combined data of all quadrants, with a total of 2976 (+437, -444) counts. The local mean background count rate was 1776 (+8, -7) counts/s. We measure a T90 of 13 (+3, -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/41978. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40044] GRB 250920B: AstroSat CZTI detection
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41977 SUBJECT: GRB 250920B: AstroSat CZTI detection DATE: 25/09/25 04:20:37 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> S. Salunke (IUCAA), Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), A. Goyal (IITB), A. Arya (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 250920B which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 41897), Swift/BAT (Gupta et. al., GCN Circ. 41898), Konus-Wind (Svinkin et. al., GCN Circ. 41942), and Glowbug (Cheung et al., GCN Circ. 41937). 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 2025-09-20 08:46:36.25 UTC. The measured peak count rate associated with the burst is 104 (+43, -20) counts/s above the background in the combined data of three quadrants (out of four), with a total of 255 (+116, -121) counts. The local mean background count rate was 214 (+3, -4) counts/s. Using cumulative rates, we measure a T90 of 7.5 (+1.3, -5.2) 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 2025-09-20 08:46:36.25 UTC. The measured peak count rate associated with the burst is 234 (+66, -52) counts/s above the background in the combined data of all quadrants, with a total of 1063 (+321, -341) counts. The local mean background count rate was 1304 (+7, -8) counts/s. We measure a T90 of 10 (+2, -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/41977. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40043] GRB 250924A: SVOM/VT optical observation
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41976 SUBJECT: GRB 250924A: SVOM/VT optical observation DATE: 25/09/25 03:51:53 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y. N. Ma, L. P. Xin, Z. H. Yao, Y. L. Qiu, C. Wu, H. L. Li, 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), R. Z. Li (YNAO), D. F. Kong (GXU), report on behalf of the SVOM/VT team: SVOM/VT performed a Target of Opportunity observation of GRB 250924A detected by Swift (Siegel et al., GCN 41959; Osborne et al., GCN 41973; Campana et al., GCN 41974; Siegel et al., GCN 41975). SVOM/VT began observing the field at 2025-09-24T11:07:35 UTC, 2.818 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical counterpart is detected in both VT_B and VT_R, the magnitudes are as follows: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 3.103 | 38*50 | VT_B | 21.15 | 0.06 3.089 | 40*50 | VT_R | 20.25 | 0.05 Our photometry was not corrected for Galactic extinction. The position and the brightness are consistent with the previous reports (Siegel et al., GCN 41959; Becerra et al., GCN 41960; Lipunov et al., GCN 41962; Schneider et al., GCN 41963; Freeberg et al., GCN 41968; Pankov et al., GCN 41969; Zheng et al., GCN 41970; Saikia et al., GCN 41971; Mo et al., GCN 41972; Siegel et al., GCN 41975). 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/41976. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40042] GRB 250924A: Swift/UVOT Detection
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41975 SUBJECT: GRB 250924A: Swift/UVOT Detection DATE: 25/09/24 23:25:48 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250924A 193 s after the BAT trigger (Siegel et al., GCN Circ. 41959). A source consistent with the XRT position is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 03:27:29.66 = 51.87358 (deg.) Dec (J2000) = +74:39:34.0 = 74.65945 (deg.) with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 193 342 147 17.80 +/- 0.04 v 681 1234 58 >18.4 b 606 626 19 18.75 +/- 0.30 u 351 601 246 18.03 +/- 0.08 w1 730 1110 39 >19.0 m2 1065 1085 19 >17.6 w2 656 1210 78 >19.6 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.315 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41975. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40041] GRB 250924A: Swift-XRT refined Analysis
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41974 SUBJECT: GRB 250924A: Swift-XRT refined Analysis DATE: 25/09/24 21:44:35 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Campana (INAF-OAB), A. Melandri (INAF-OAR), D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), T. Sbarrato (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 8.3 ks of XRT data for GRB 250924A, from 181 s to 34.9 ks after the trigger. The data comprise 80 s in Windowed Timing (WT) mode (the first 1 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The light curve can be modelled with an initial power-law decay with an index of alpha=5.2 (+/-0.5), followed by a break at T+301 s to an alpha of 1.05 (+/-0.05). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 4.0 (+0.4, -0.3). The best-fitting absorption column is 5.1 (+/-0.8) x 10^21 cm^-2, in excess of the Galactic value of 2.8 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.06 (+0.20, -0.13) and a best-fitting absorption column consistent with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (5.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.8 (+0.7, -0.0) x 10^21 cm^-2 Galactic foreground: 2.8 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 2.06 (+0.20, -0.13) If the light curve continues to decay with a power-law decay index of 1.05, the count rate at T+24 hours will be 8.0 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.9 x 10^-13 (4.4 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/01351790. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41974. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40040] GRB 250924A: Enhanced Swift-XRT position
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41973 SUBJECT: GRB 250924A: Enhanced Swift-XRT position DATE: 25/09/24 21:34:07 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 985 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250924A, 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 = 51.87237, +74.65846 which is equivalent to: RA (J2000): 03h 27m 29.37s Dec (J2000): +74d 39' 30.5" with an uncertainty of 2.2 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/41973. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40039] GRB 250924A: J-band detection with WINTER
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41972 SUBJECT: GRB 250924A: J-band detection with WINTER DATE: 25/09/24 19:38:12 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 250924A (Siegel et al., GCN 41959) 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 2025-09-24T08:26:28 UTC in the J band (~8 minutes 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 detect a clear source at the optical counterpart location (Siegel et al., GCN 41959; Becerra et al., GCN 41960; Lipunov et al., GCN 41962; Schneider et al., GCN 41963; Freeberg et al., GCN 41968; Pankov et al., GCN 41969; Zheng et al., GCN 41970; Saikia et al., GCN 41971), with magnitude J ~ 18.6 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/41972. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40038] GRB 250924A: GROWTH-India Telescope Upper Limits
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41971 SUBJECT: GRB 250924A: GROWTH-India Telescope Upper Limits DATE: 25/09/24 18:08:50 GMT FROM: Varun Bhalerao at IIT Bombay <varunb(a)iitb.ac.in> A.P. Saikia, T. Mohan, V. Swain, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and R. Norbu (IAO) report on behalf of the GIT team: We observed the field of Swift GRB 250924A (Siegel et al., GCN 41959), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-09-24 14:01:24 UT, i.e., 5.7 hours after the GRB trigger. We obtained multiple exposures in r'. We did not detect the source in our stacked image within the Swift UVOT localization region (Siegel et al., GCN 41959). The photometric upper limits are as follows: | MJD (mid) | Filter | tmid-t0 (hr) | Exposure Time (sec) | Upper limit (AB) | | ------------ | ------ | ------------ | ------------------- | ---------------- | | 60942.618958 | r' | 6.55 | 11 x 360 | 21.5 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our observations span a similar time frame as Pankov et al. (GCN 41969), and are broadly consistent with their measurements. The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/41971. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40037] GRB 250924A: KAIT optical observations
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41970 SUBJECT: GRB 250924A: KAIT optical observations DATE: 25/09/24 17:33:43 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, automatically responded to the Swift GRB 250924A (Siegel et al., GCN 41959) starting at 08:21:50 UT, 201s after the burst. Observations lasted for about 1 hour with degraded sky condition (cloudy), and a set of clear (roughly R) filter images were obtained. We clearly detected the reported fading afterglow (Siegel et. al, GCN 41959; Becerra et. al, GCN 41960; Schneider et. al, GCN 41963; Freeberg et. al, GCN 41968; Pankov et al., GCN 41969). We measure its brightness decayed from 16.41 +/- 0.03 mag (Vega) at 3.52 minutes to 19.7 +/- 0.3 mag at 59.33 minutes after the burst. The data after 300s can be fit with a single power law with a decay index of -0.96 +/- 0.02. View this GCN Circular online at https://gcn.nasa.gov/circulars/41970. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40036] GRB 250924A: Mondy optical observations, afterglow fading
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41969 SUBJECT: GRB 250924A: Mondy optical observations, afterglow fading DATE: 25/09/24 16:19:46 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), E. Klunko (ISTP) report on behalf of GRB-IKI-FuN: We observed the field of GRB 250924A detected by Swift (Siegel et. al, GCN 41897) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy). We are obtaining the images of the GRB field in the R-filter. The optical afterglow initially detected by Swift/UVOT (Siegel et. al, GCN 41897) and further observed by (Becerra et. al, GCN 41960; Schneider et. al, GCN 41963; Freeberg et. al, GCN 41968) is clearly visible in the stacked image of first 10 obtained images. Preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err. UL (nxs) (mid, days) (3sigma) 2025-09-24 14:37:48 10x120 0.27036 R 21.47 0.09 22.5 The photometry was calibrated against nearby USNO-B1.0 stars (R2-mags) and not corrected for the Galactic extinction. We note that the afterglow has faded at ~3.7 mag in ~6.5 hr since detection. Further observations are ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/41969. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40035] GRB 250924A: Kilonova-Catcher optical afterglow detection
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41968 SUBJECT: GRB 250924A: Kilonova-Catcher optical afterglow detection DATE: 25/09/24 14:39:52 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Freeberg (KNC), C. Andrade(UMN), D. Turpin (CEA-Saclay/Irfu), S. Antier (OCA/IJCLab), M. Coughlin (UMN),S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 250924A detected by Swift/BAT (Siegel et al., GCN 41959) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC160FL telescope operated by M. Freeberg. Our observations started at TGRB+1.0hr. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we detect the optical counterpart reported by Swift/UVOT (Siegel et al., GCN 41959), DDOTI (Becerra et al., GCN 41960) and COLIBRI (Schneider et al., GCN 41963). We report our follow-up results in the table below +---------------+-----------+--------+----------------+-------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+========+================+=============+ | 1.63 | 8 x 300s | r (AB) | 20.03 +/- 0.10 | TEC160FL | | 2.64 | 18 x 180s | i (AB) | 19.76 +/- 0.19 | TEC160FL | +---------------+-----------+--------+----------------+-------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41968. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40034] GRB 250920C: Kilonova-Catcher optical afterglow detection
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41967 SUBJECT: GRB 250920C: Kilonova-Catcher optical afterglow detection DATE: 25/09/24 14:37:22 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Freeberg (KNC), C. Andrade(UMN), D. Turpin (CEA-Saclay/Irfu), S. Antier (OCA/IJCLab), M. Coughlin (UMN),S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 250920C detected by Fermi/GBM (Fermi GBM team, GCN 41903), Swift/BAT (Gupta et al., GCN 41904), SVOM/GRM (Wang et al., GCN 41929) and Konus-WIND (Panteleeva et al., GCN 41957) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iTelescope T30 telescope operated by M. Freeberg. Our observations started at TGRB+3.3hr. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we detect the optical/IR counterpart reported by GOTO (Wortley et al., GCN 41907) and further confirmed by many other teams (Strausbaugh et al.,GCN 41911; Ghosh et al., GCN 41913; Kuin et al., GCN 41920; Mohan et al., GCN 41925; Sanchez-Ramirez et al., GCN 41928; Guiffreda et al., GCN 41943; Mo et al., GCN 41947; de Ugarte Postigo et al., GCN 41951; de Wet et al., GCN 41952; Izzo et al., GCN 41955; Zheng et al., GCN 41956; Zhu et al., GCN 41965) We report some of our first image follow-up results in the table below +---------------+----------+-----------+----------------+--------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+==========+===========+================+==============+ | 3.49 | 3 x 300s | Rc (Vega) | 18.93 +/- 0.07 | iT30 | +---------------+----------+-----------+----------------+--------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the Johnson-cousins filters were calibrated using the GAIA DR3 synphot catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41967. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40033] GRB 250922B: SVOM/GRM observation
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41966 SUBJECT: GRB 250922B: SVOM/GRM observation DATE: 25/09/24 14:10:14 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang. Wen-Jun Tan, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by a burst GRB 250922B at 2025-09-22T21:13:25.900 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41944). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.07 +0.05/-0.03 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250922B.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 48.7, DEC= 30.7, GCN#41944), is located at about 52 degrees from the SVOM optical axis, which is just outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-0.2 to T0+0.1 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.15 +0.12/-0.15 and the cutoff energy, parameterized as Epeak, is 1060 +110/-460 keV. The event fluence (10-1000 keV) in this time interval is (4.38 +0.55/-0.53)E-07 erg/cm^2. The 'Amati' relation of GRB 250922B is shown at: https://www.bursthub.cn//admin/static/svgrb250922B_amati.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41966. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40032] GRB 250920C: TRT optical observation
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41965 SUBJECT: GRB 250920C: TRT optical observation DATE: 25/09/24 13:37:17 GMT FROM: Zipei Zhu at NAOC <zpzhu(a)nao.cas.cn> Z.P. Zhu (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), L.B. He, X. Liu, J. An, S.Q. Jiang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of GRB 250920C (Fermi GBM team, GCN 41903; Gupta et al., GCN 41904; Mailyan & Meegan, GCN 41917; Gupta et al., GCN 41924; Wang et al., GCN 41929; Panteleeva et al., GCN 41957 ), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observations started at 18:21:14 UTC on 2025-09-20, i.e., ~ 2.9 hours after the Swift/BAT trigger and a series of frames in the R band were obtained. The optical afterglow (Wortley et al., GCN 41907; Strausbaugh et al., GCN 41911; Ghosh et al., GCN 41913; Kuin et al., GCN 41920; Mohan et al., GCN 41925; Sanchez-Ramirez et al., GCN 41928; Guiffreda et al., GCN 41943; de Ugarte Postigo et al., GCN 41951; de Wet et al., GCN 41952; Izzo et al., GCN 41955; Zheng & Filippenko, GCN 41956; ) was clearly detected in our stacked R-band frame with a brightness of 18.87 +/- 0.02, calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41965. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40031] GRB 250924B: Fermi GBM Final Localization
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41964 SUBJECT: GRB 250924B: Fermi GBM Final Localization DATE: 25/09/24 13:25:19 GMT FROM: Padraig McDermott at University College Dublin <padraig.mcdermott(a)ucdconnect.ie> The Fermi GBM team reports the detection of a likely SHORT GRB "At 10:26:58.90 UT on 24 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB250924B (trigger 780402423/250924435). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 306.44, Dec = -61.82 (J2000 degrees, equivalent to J2000 20h 25m, -61d 49'), with a statistical uncertainty of 9.50 degrees. The angle from the Fermi LAT boresight is 150 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250924435/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250924435/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250924435/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41964. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40030] GRB 250924A: COLIBRÍ optical observations
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41963 SUBJECT: GRB 250924A: COLIBRÍ optical observations DATE: 25/09/24 12:35:04 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Camila Angulo (UNAM), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Rosa L. Becerra (U Roma), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU), 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) and Ny Avo Rakotondrainibe (LAM): We imaged the field of the Swift GRB 250924A (Siegel et al., GCN Circ. 41959) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-09-24 08:33:51 to 09:46:24 UTC (from 15 to 88 minutes after the trigger) and obtained images in the g, r, i, z and y 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. We detect the optical counterpart reported by source Siegel et al., GCN Circ. 41959 and Becerra et al., GCN Circ. 41960 at: RA(J2000) = 3:27:29.71 = 51.8738 degrees Dec(J2000) = +74:39:33.7 = +74.6594 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitudes derived for that source are: Start (UT) | mid T0+T (s) | Band | Exp | Mag | Error --------------------|---------------|------|------|------|------ 2025-09-24T09:01:29 | 2853 | g | 3x60 | 20.12 | 0.05 2025-09-24T08:33:51 | 1054 | r | 3x60 | 18.90 | 0.04 2025-09-24T09:03:50 | 2994 | i | 3x60 | 19.38 | 0.05 2025-09-24T08:33:51 | 1054 | z | 3x60 | 18.39 | 0.05 2025-09-24T09:02:40 | 3963 | y | 16x60 | 19.26 | 0.06 From subsequent r-band images obtained between 0.26 and 2.21 hr after the burst, we measure a temporal decay slope of alpha = 0.6 +/- 0.1. Further observations are ongoing. 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/41963. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40029] Swift GRB 250924A: Global MASTER-Net observations report
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41962 SUBJECT: Swift GRB 250924A: Global MASTER-Net observations report DATE: 25/09/24 12:04:41 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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the Swift GRB 250924A ( M. H. Siegel et al., GCN 41959) errorbox 13196 sec after notice time and 13280 sec after trigger time at 2025-09-24 11:59:49 UT, with upper limit up to 16.2 mag. Observations started at twilight. The observations began at zenith distance = 49 deg. The sun altitude is -10.0 deg. The galactic latitude b = 15 deg., longitude l = 133 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2998975 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 13310 | MASTER-Tunka | C | 60 | 16.2 | 13310 | MASTER- | C | 60 | 16.2 | Coadd 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/41962. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40028] GRB 250919A / EP250919a: further LCO optical observation
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41961 SUBJECT: GRB 250919A / EP250919a: further LCO optical observation DATE: 25/09/24 11:30:34 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), J. T. Palmerio (CEA/Irfu), Z. Q. Wang (GXU), Y. F. Liang (PMO), report on behalf of the SVOM mission team: We re-observed the field of GRB 250919A / EP250919a (Fermi GBM Team, GCN 41874; Liang et al., GCN 41879; Wang et al., GCN 41882; Holzmann Airasca et al., GCN 41884; Waratkar et al., GCN 41888; Cheung et al., GCN 41891; Wang et al. GCN 41900; Frederiks et al. GCN 41905) with the LCO 1m telescope at Siding Spring Observatory equipped with the Sinistro instrument. We obtained 3x200 s exposures in the SDSS r filter. The optical counterpart (Li et al., GCN 41877; Levan et al., GCN 41883; Oates et al., GCN 41886; Lipunov et al., GCN 41893; Ma et al. GCN 41894, Saccardi et al., GCN 41906) is still clearly detected in our subtracted image (using the Legacy Survey DR10 image template) with the following magnitude (calibrated against the SkyMApper DR4 catalogued stars, not corrected for Galactic extinction): r = 20.67 +/- 0.08 (AB), at a mid-time of 4.47 days after the trigger. Compared to our first epoch (Saccardi et al., GCN 41906), the afterglow is fading as a power law decay with alpha ~ 1.1 with no evidence of any late break so far. Further observations are planned. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/41961. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40027] GRB 250924A: DDOTI Detection of the Optical Counterpart
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41960 SUBJECT: GRB 250924A: DDOTI Detection of the Optical Counterpart DATE: 25/09/24 09:00:57 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Sahil Atri (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of GRB 250924A detected by Swift (Siegel et al., GCN Circ. 41959) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-09-24 UTC. DDOTI observed the Swift/UVOT position (Siegel et al., GCN Circ. 41959) from 08:35 UTC to 08:40 UTC (from T+17.3 to T+ 22.1 min after the trigger), obtaining a total exposure of 4 minutes. By comparing our observations with the USNO-B1 and Pan-STARRS PS1 DR2 catalogs, we detect an uncatalogued source with a preliminary AB magnitude of: w = 19.47 +/- 0.05. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/41960. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40026] GRB 250924A: Swift detection of a burst with an optical counterpart
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41959 SUBJECT: GRB 250924A: Swift detection of a burst with an optical counterpart DATE: 25/09/24 08:35:33 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> M. H. Siegel (PSU), J. J. DeLaunay (PSU), R. Gupta (NASA GSFC), S. Lanava (PSU), K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 08:18:29 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250924A (trigger=1351790). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 51.865, +74.652 which is RA(J2000) = 03h 27m 28s Dec(J2000) = +74d 39' 07" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 30 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~17 sec after the trigger. The XRT began observing the field at 08:21:32.8 UT, 183.6 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 51.87141, 74.65894 which is equivalent to: RA(J2000) = 03h 27m 29.14s Dec(J2000) = +74d 39' 32.2" with an uncertainty of 2.7 arcseconds (radius, 90% containment). This location is 25 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 2.77 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 1.03e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 192 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 03:27:29.62 = 51.87340 DEC(J2000) = +74:39:34.0 = 74.65945 with a 90%-confidence error radius of about 0.62 arc sec. This position is 1.6 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.74 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.316. Burst Advocate for this burst is M. H. Siegel (siegel AT swift.psu.edu) 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/41959. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40025] GRB 250920B: AbAO optical upper limits
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41958 SUBJECT: GRB 250920B: AbAO optical upper limits DATE: 25/09/23 21:32:13 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), R. Ya. Inasaridze (AbAO) report on behalf of GRB-IKI-FuN: We observed the field of a long GRB 250920B detected by Fermi/GBM (The Fermi GBM team GCN 41897), Swift (Gupta et. al, GCN 41898), with the AS-32 0.7m telescope of AbAO. We obtained two series of images in the R band on epochs 2025-09-22 and 2025-09-23 (~2.3 and ~3.3 days since trigger, respectively). The optical afterglow initially detected by Swift/UVOT (Gupta et. al, GCN 41898) and further observed by (WU et. al, GCN 41908; Hall et. al, GCN 41914; Pankov et. al, GCN 41931; Reguitti et. al, GCN 41932; Moskvitin et. al, GCN 41948; Pankov et. al, GCN 41953) is not detected in the stacked images of both epochs. Preliminary upper limits are as follows: Date UTstart Exptime t-T0 Filter OT Err. UL (nxs) (mid, days) (3sigma) 2025-09-22 16:09:15 20x2+97x30 2.32458 R n/d n/d 20.3 2025-09-23 16:04:34 153*30 3.33076 R n/d n/d 20.3 The photometry was calibrated against nearby PS1 DR2 stars (R-mags obtained via Lupton 2005 transformations) and not corrected for the Galactic extinction. Ref. stars PS1 DR2 (Lupton 2005) RA Dec R R_err 187.24325 47.82521 15.134 0.007 187.41433 47.78151 14.974 0.008 View this GCN Circular online at https://gcn.nasa.gov/circulars/41958. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40024] Konus-Wind detection of GRB 250920C
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41957 SUBJECT: Konus-Wind detection of GRB 250920C DATE: 25/09/23 19:12:38 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 250920C (Fermi-GBM detection: The Fermi GBM team, GCN 41903; Mailyan & Meegan, GCN 41917; Swift-BAT detection: Gupta et al., GCN 41904; Gupta et al., GCN 41924; SVOM-GRM observaion: Wang et al., GCN 41929) triggered Konus-Wind at T0=55519.312 s UT (15:25:19.312). The burst light curve shows a multipeaked structure which starts at ~T0-0.4 s and has a total duration of ~41 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250920_T55519/ As observed by Konus-Wind, the burst had the total fluence of 2.91(-0.21,+0.29)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+25.904 s, of 8.27(-0.78,+0.78)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+41.216 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.22(-0.07,+0.09), the high energy photon index beta = -3.19(-6.81,+0.51), the peak energy Ep = 160(-12,+9) keV (chi2 = 104/97 dof). The spectrum near the maximum count rate (measured from T0+24.832 to T0+33.024 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.14(-0.07,+0.07) and Ep = 220(-14,+16) keV (chi2 = 96/81 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.15 (chi2 = 97/80 dof). Assuming the redshift z=1.399 (Sanchez-Ramirez et al., GCN 41928; Izzo et al., GCN 41955) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is 1.54(-0.11,+0.16)x10^53 erg, the peak luminosity L_iso is 1.05(-0.10,+0.10)x10^53 erg/s, the rest-frame peak energy of the time-averaged spectrum Ep,i,z is 383(-30,+22) keV and the spectrum near the maximum count rate Ep,p,z is 528(-33,+38) keV. With the obtained estimates, GRB 250920C is inside 68% prediction bands for both the 'Amati' and the 'Yonetoku' relations derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB250920_T55519/GRB250920C_rest_frame.pdf All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/41957. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40023] GRB 250920C: KAIT optical observations
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41956 SUBJECT: GRB 250920C: KAIT optical observations DATE: 25/09/23 18:23:18 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of GRB 250920C (Fermi GBM team, GCN 41903; Gupta et al., GCN 41904; Mailyan et al., GCN 41917; Gupta et al., GCN 41924; SVOM Team, GCN 41929) around mid time of ~0.778d after the burst. A set of 90x60s clear (roughly R) filter images were obtained. We marginally detected the optical afterglow (Wortley et al., GCN 41907; Strausbaugh et al., GCN 41911; Ghosh et al., GCN 41913; Lipunov et al., GCN 41916; Kuin et al., GCN 41920; Mohan et al., GCN 41925; Sanchez-Ramirez et al., GCN 41928; Guiffreda et al., GCN 41943; de Ugarte Postigo et al., GCN 41951). We estimate the afterglow to be 21.0 +/- 0.3 mag (Vega). View this GCN Circular online at https://gcn.nasa.gov/circulars/41956. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40022] GRB 250920C: VLT redshift confirmation z = 1.399
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41955 SUBJECT: GRB 250920C: VLT redshift confirmation z = 1.399 DATE: 25/09/23 16:00:11 GMT FROM: Valentina Abril-Melgarejo at Obs. Paris/LUX <valentina.abril-melgarejo(a)obspm.fr> L. Izzo (INAF/OACn and DARK/NBI), D. Xu (NAOC), V. Abril-Melgarejo (LUX-Paris Obs.), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), N. R. Tanvir (Leicester), V. D’Elia (ASI/SSDC), report on behalf of the Stargate collaboration: We observed the optical afterglow (Wortley et al., GCN 41907) of GRB 250920C (Gupta et al., GCN 41904), using the ESO VLT UT4 (Yepun) equipped with the MUSE spectrograph. The mid time of our observation was Jan 21.209 UT (10.41 hr after the GRB trigger), and consisted of 4 exposures of 19 min each. We extracted a 1D spectrum using a circular aperture of 0.4 arcsec radius, centered on the afterglow emission. In the reduced spectrum, which covers the wavelength range 4750 - 9330 AA, we detect clear continuum and a number of absorption features, which we identify, among others, as Mg II, Mg I, Fe II, Fe II*, Ni II*, Cr II, Zn II, Mn II, all at a common redshift z = 1.399. The detection of Fe II fine-structure lines cements the association of the GRB with this absorption system. Furthermore, an emission line consistent with [O II] at the same redshift is also detected, likely from the underlying host galaxy (Wortley et al., GCN 41907). Our result is thus fully consistent, and strengthens, the previous reports by GTC (Sanchez-Ramirez et al., GCN 41928) and SALT (De Wet et al.. GCN 41952). We acknowledge expert support from the observing staff in Paranal, in particular Boris Haeussler, Enrico Congiu, Ana Jimenez Gallardo, and Marcelo Lopez. View this GCN Circular online at https://gcn.nasa.gov/circulars/41955. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40021] GRB 250920C: VLT redshift confirmation z = 1.399
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41955 SUBJECT: GRB 250920C: VLT redshift confirmation z = 1.399 DATE: 25/09/23 16:00:11 GMT FROM: Valentina Abril-Melgarejo at Obs. Paris/LUX <valentina.abril-melgarejo(a)obspm.fr> L. Izzo (INAF/OACn and DARK/NBI), D. Xu (NAOC), V. Abril-Melgarejo (LUX-Paris Obs.), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), N. R. Tanvir (Leicester), V. D’Elia (ASI/SSDC), report on behalf of the Stargate collaboration: We observed the optical afterglow (Wortley et al., GCN 41907) of GRB 250920C (Gupta et al., GCN 41904), using the ESO VLT UT4 (Yepun) equipped with the MUSE spectrograph. The mid time of our observation was Jan 21.209 UT (10.41 hr after the GRB trigger), and consisted of 4 exposures of 19 min each. We extracted a 1D spectrum using a circular aperture of 0.4 arcsec radius, centered on the afterglow emission. In the reduced spectrum, which covers the wavelength range 4750 - 9330 AA, we detect clear continuum and a number of absorption features, which we identify, among others, as Mg II, Mg I, Fe II, Fe II*, Ni II*, Cr II, Zn II, Mn II, all at a common redshift z = 1.399. The detection of Fe II fine-structure lines cements the association of the GRB with this absorption system. Furthermore, an emission line consistent with [O II] at the same redshift is also detected, likely from the underlying host galaxy (Wortley et al., GCN 41907). Our result is thus fully consistent, and strengthens, the previous reports by GTC (Sanchez-Ramirez et al., GCN 41928) and SALT (De Wet et al.. GCN 41952). We acknowledge expert support from the observing staff in Paranal, in particular Boris Haeussler, Enrico Congiu, Ana Jimenez Gallardo, and Marcelo Lopez. View this GCN Circular online at https://gcn.nasa.gov/circulars/41955. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40020] EP250911a: e-MERLIN radio observations
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41954 SUBJECT: EP250911a: e-MERLIN radio observations DATE: 25/09/23 12:59:20 GMT FROM: Giulia Gianfagna at INAF-IAPS <giulia.gianfagna(a)inaf.it> G. Gianfagna, G. Bruni, L. Piro, A. L. Thakur (INAF-IAPS) report: We observed the Fast X-ray Transient EP250911a (Liang et al., GCN 41788) with the e-MERLIN radio telescope under the project CY20206 (PI: Gianfagna) at 5 GHz starting on Sep. 17, 16:00 UT (~6 days after the EP trigger) for a total of 11 hours. 1331+3030 was used for flux scale calibration, and 2344+2952 for complex gain. The beam size was 63x37 milli-arcsec. Data was reduced with the e-MERLIN pipeline and imaged with CASA. The image RMS was 18 uJy/beam. We did not find statistically significant emission at a level above 5-sigma at the position of the optical counterpart reported by Quirola-Vasquez et al. (GCN 41790), Angulo et al (GCN 41793), Lai et al. (GCN 41801), Moskvitin et al. (GCN 41805), Ma et al. (GCN 41807), Malesani et al. (GCN 41811). Thus, we estimate a 5-sigma upper limit of ~ 90 uJy at 5 GHz. Further e-Merlin observations are planned. We thank the e-Merlin staff for the prompt scheduling of these observations. e-MERLIN is a National Facility operated by the University of Manchester at Jodrell Bank Observatory on behalf of STFC, part of UK Research and Innovation. View this GCN Circular online at https://gcn.nasa.gov/circulars/41954. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40019] GRB 250920B: CrAO ZTSH optical observations
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41953 SUBJECT: GRB 250920B: CrAO ZTSH optical observations DATE: 25/09/23 12:38:45 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), V. Rumyantsev (CrAO) report on behalf of GRB-IKI-FuN: We observed the field of a long GRB 250920B detected by Fermi/GBM (The Fermi GBM team GCN 41897), Swift (Gupta et. al, GCN 41898), with the ZTSH telescope of CrAO. We obtained series of images in R,V bands starting on 2025-09-21 at 16:28:47.74 UT, i.e. 1.321 days since Fermi/GBM trigger. The optical afterglow initially detected by Swift/UVOT (Gupta et. al, GCN 41898) and further observed by (WU et. al, GCN 41908; Hall et. al, GCN 41914; Pankov et. al, GCN 41931; Reguitti et. al, GCN 41932; Moskvitin et. al, GCN 41948) is clearly visible in individual 120 s exposures taken in the R-band. Preliminary photometry of the OT in the R-band is as follows: Date UTstart Exptime t-T0 Filter OT Err. UL (s) (mid, days) (3sigma) 2025-09-21 17:21:58 120 1.35870 R 20.7 0.1 22 The photometry was calibrated against nearby USNO-B1.0 stars (R2 mags) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41953. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40018] GRB 250920C: SALT redshift confirmation
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41952 SUBJECT: GRB 250920C: SALT redshift confirmation DATE: 25/09/23 12:27:05 GMT FROM: Simon de Wet at DTU Space <simdewet(a)gmail.com> S. de Wet (DTU Space), D. A. H. Buckley (SAAO), D. B. Malesani (DAWN/NBI and Radboud), P. J. Groot (Radboud, UCT, and SAAO) report: We observed the optical afterglow (Wortley et al., GCN 41907) of GRB 250920C (Gupta et al., GCN 41904), using the Southern African Large Telescope (SALT) equipped with the Robert Stobie Spectrograph (RSS). Observations started at 23:11:13 UT on 2025 Sep 20 (7.8 hr after the GRB), and consisted of 2x1200 s of spectroscopy using the PG700 grating (which covers the wavelength range 3600-7500 AA). In the coadded spectrum, continuum is detected across the whole wavelength range. A few narrow absorption features are visible which we interpret as due to C IV 1548,1550 (very strong), Fe II 2344 and 2374, Mg II 2796,2803 and Mg I 2852, all at a redshift of 1.399. Our result is thus consistent with, and confirms, the earlier measurement reported by Sanchez-Ramirez et al. (GCN 41928) using the GTC. View this GCN Circular online at https://gcn.nasa.gov/circulars/41952. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40017] GRB 250920C: COLIBRÍ optical observations
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41951 SUBJECT: GRB 250920C: COLIBRÍ optical observations DATE: 25/09/23 11:33:46 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Fredd Alvarez (UNAM), 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), and Benjamin Schneider (LAM): We imaged the field of the Fermi/GBM GRB 250920C (Fermi GBM team, GCN Circ. 41903; Mailyan et al. GCN 41917), also detected by Swift/BAT (Gupta et al. GCN 41904; Gupta et al. GCN 41924) and SVOM/GRM (Wang et al. GCN 41929) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-09-23 08:01:47 to 10:19:49 UTC (from 2.69 to 2.75 days after the trigger) and obtained 64 minutes of simultaneous exposures 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. We detected the optical counterpart reported by Wortley et al. (GCN Circ. 41907), at preliminary magnitudes of: r = 22.70 +/- 0.14 z = 22.54 +/- 0.25 We note that the source is still significantly brighter than the candidate host galaxy identified by Wortley et al. (GCN Circ. 41907) which appears in the Legacy Survey with r ~ 25.1 mag, so our observations are still afterglow dominated. Further observations and analysis are ongoing. 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/41951. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40016] GRB 250922C: AstroSat CZTI detection of a short burst
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41950 SUBJECT: GRB 250922C: AstroSat CZTI detection of a short burst DATE: 25/09/23 05:51:16 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (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 a short-duration GRB 250922C. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-09-22 19:53:50.45 UTC. The measured peak count rate associated with the burst is 407 (+136, -92) counts/s above the background in the combined data of three quadrants (out of four), with a total of 137 (+46, -45) counts. The local mean background count rate was 253 (+8, -11) counts/s. Using cumulative rates, we measure a T90 of 0.43 (+0.45, -0.15) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-09-22 19:53:50.73 UTC. The measured peak count rate associated with the burst is 291 (+66, -72) counts/s above the background in the combined data of all quadrants, with a total of 477 (+186, -198) counts. The local mean background count rate was 1436 (+10, -12) 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/41950. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40015] Fermi GRB 250922B: Global MASTER-Net observations report
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41949 SUBJECT: Fermi GRB 250922B: Global MASTER-Net observations report DATE: 25/09/23 00:15:31 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) started inspect of the Fermi GRB 250922B ( Fermi GBM team, GCN 41944) errorbox 5589 sec after notice time and 5627 sec after trigger time at 2025-09-22 22:47:13 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 30 deg. The sun altitude is -41.0 deg. The galactic latitude b = -22 deg., longitude l = 156 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2997538 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 5658 | 2025-09-22 22:47:13 | MASTER-Kislovodsk | (02h 52m 08.73s , +16d 41m 59.3s) | C | 60 | 18.8 | 5658 | 2025-09-22 22:47:13 | MASTER-Kislovodsk | (02h 56m 55.92s , +16d 18m 34.3s) | C | 60 | 18.7 | 6457 | 2025-09-22 23:00:32 | MASTER-Kislovodsk | (02h 52m 08.19s , +16d 41m 21.3s) | C | 60 | 18.7 | 6457 | 2025-09-22 23:00:32 | MASTER-Kislovodsk | (02h 56m 45.35s , +16d 19m 01.1s) | C | 60 | 18.8 | 7065 | 2025-09-22 23:10:41 | MASTER-Kislovodsk | (02h 52m 03.78s , +16d 43m 29.5s) | C | 60 | 18.7 | 7065 | 2025-09-22 23:10:41 | MASTER-Kislovodsk | (02h 56m 46.03s , +16d 21m 14.1s) | C | 60 | 18.7 | 7673 | 2025-09-22 23:20:48 | MASTER-Kislovodsk | (02h 52m 13.12s , +16d 43m 24.9s) | C | 60 | 18.6 | 7673 | 2025-09-22 23:20:48 | MASTER-Kislovodsk | (02h 56m 52.90s , +16d 21m 12.4s) | C | 60 | 18.5 | 8471 | 2025-09-22 23:34:06 | MASTER-Kislovodsk | (02h 52m 00.64s , +16d 41m 56.3s) | C | 60 | 18.6 | 8471 | 2025-09-22 23:34:06 | MASTER-Kislovodsk | (02h 56m 50.35s , +16d 19m 34.7s) | C | 60 | 18.4 | 9420 | 2025-09-22 23:49:55 | MASTER-Kislovodsk | (02h 39m 41.84s , +18d 28m 07.8s) | C | 60 | 18.8 | 9420 | 2025-09-22 23:49:55 | MASTER-Kislovodsk | (02h 34m 54.00s , +18d 49m 39.5s) | C | 60 | 18.7 | 9916 | 2025-09-22 23:58:11 | MASTER-Kislovodsk | (02h 53m 47.82s , +18d 37m 01.6s) | C | 60 | 18.7 | 9916 | 2025-09-22 23:58:11 | MASTER-Kislovodsk | (02h 58m 39.92s , +18d 14m 12.0s) | C | 60 | 18.6 | 10088 | 2025-09-23 00:01:03 | MASTER-Kislovodsk | (02h 39m 42.06s , +18d 28m 10.1s) | C | 60 | 18.7 | 10088 | 2025-09-23 00:01:03 | MASTER-Kislovodsk | (02h 34m 54.63s , +18d 49m 36.5s) | C | 60 | 18.7 | 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/41949. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40014] GRB 250920B: SAO RAS optical observations
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41948 SUBJECT: GRB 250920B: SAO RAS optical observations DATE: 25/09/22 22:46:39 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova (SAO), N. Pankov (HSE), A. Pozanenko (IKI) report on behalf of GRB follow-up collaboration and IKI-GRB-FuN. We observed the field of the GRB 250920B (Fermi GBM Team, GCN 41897; Gupta et al., GCN 41898; Page et al., GCN 41909; Evans et al., GCN 41910; Sonawane and Meegan, GCN 41919; Sakamoto et al., GCN 41923; Cheung et al., GCN 41937; Svinkin et al., GCN 41942) with the 1-m SAO RAS telescope Zeiss-1000 equipped with CCD-photometer. We obtained 10 x 300 sec. images Rc band on September 22, 16:22:43--17:17:34 (t_mid - T0 = 2.33586 days). The optical transient (Gupta et al., GCN 41898; Wu et al., GCN 41908; Hall et al., GCN 41914; Kuin and Gupta, GCN 41915; Reguitti et al., GCN 41932) is clearly detected in the stacked frame with the brightness of R = 21.7 +/- 0.1. Date UT start t-T0 Exp. Filter OT Err. UL (3sigma) (mid, d) (s) 2025.09.22 16:22:43 2.33586 10 x 300 Rc 21.7 +/- 0.1 23.2 Preliminary photometry is based on the nearby stars from USNO-B1 (R2 magnitudes) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41948. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40013] GRB 250920C: NIR observations with WINTER
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41947 SUBJECT: GRB 250920C: NIR observations with WINTER DATE: 25/09/22 22:40:56 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (Caltech), Viraj Karambelkar (Columbia), 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 250920C (Fermi GBM Team, GCN 41903; Gupta et al., GCN 41904; Mailyan et al., GCN 41917; Goad et al., GCN 41922; Gupta et al., GCN 41924; SVOM Team, GCN 41929; Evans et al., GCN 41935) 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 2025-09-21T08:59:42.591 UTC in the J band (~17.5 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 (Wortley et al., GCN 41907; Strausbaugh et al., GCN 41911; Ghosh et al., GCN 41913; Lipunov et al., GCN 41916; Kuin et al., GCN 41920; Mohan et al., GCN 41925; Sanchez-Ramirez et al., GCN 41928; Guiffreda et al., GCN 41943). We obtain the following 5-sigma upper limit: J ~ 19.0 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/41947. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40012] GRB 250920B: NIR observations with WINTER
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41946 SUBJECT: GRB 250920B: NIR observations with WINTER DATE: 25/09/22 22:39:42 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (Caltech), Viraj Karambelkar (Columbia), 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 250920B (Fermi GBM team, GCN 41897; Gupta et al., GCN 41898; Page et al., GCN 41909; Evans et al., GCN 41910; Sonawane et al., GCN 41919; Sakamoto et al., GCN 41923; Cheung et al., GCN 41937) 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 2025-09-21T02:30:43.439 UTC in the J band (~17.7 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 candidate location (Lipunov et al., GCN 41901; Wu et al., GCN 41908; Hall et al., GCN 41914; Kuin et al., GCN 41915; Pankov et al., GCN 41931; Reguitti et al., GCN 41932). We obtain the following 5-sigma upper limit: J ~ 18.9 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/41946. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40011] Fermi trigger No 780156732: Global MASTER-Net observations report
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41945 SUBJECT: Fermi trigger No 780156732: Global MASTER-Net observations report DATE: 25/09/22 21:31:17 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB250921.59 (trigger No 780156732,20h 24m 04.08s , +00d 33m 00.0s, R=33.5) errorbox 42698 sec after notice time and 42707 sec after trigger time at 2025-09-22 02:03:54 UT, with upper limit up to 20.3 mag. The observations began at zenith distance = 26 deg. The sun altitude is -44.3 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB250921.59 errorbox 1 days 6573 sec after notice time and 1 days 6582 sec after trigger time at 2025-09-22 16:01:50 UT, with upper limit up to 17.7 mag. Observations started at twilight. The observations began at zenith distance = 38 deg. The sun altitude is -10.5 deg. MASTER-SAAO robotic telescope located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB250921.59 errorbox 1 days 17595 sec after notice time and 1 days 17604 sec after trigger time at 2025-09-22 19:05:31 UT, with upper limit up to 19.4 mag. The observations began at zenith distance = 43 deg. The sun altitude is -32.0 deg. The galactic latitude b = -21 deg., longitude l = 45 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2996777 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 42737 | 2025-09-22 02:03:54 | MASTER-OAFA | (19h 50m 28.63s , -19d 46m 33.6s) | C | 60 | 19.6 | 42813 | 2025-09-22 02:05:10 | MASTER-OAFA | (19h 59m 04.47s , -19d 46m 40.4s) | C | 60 | 19.9 | 42985 | 2025-09-22 02:08:02 | MASTER-OAFA | (19h 50m 31.65s , -19d 46m 10.8s) | C | 60 | 19.6 | 43060 | 2025-09-22 02:09:17 | MASTER-OAFA | (19h 59m 05.00s , -19d 44m 57.1s) | C | 60 | 19.8 | 43229 | 2025-09-22 02:12:06 | MASTER-OAFA | (19h 50m 28.14s , -19d 44m 25.3s) | C | 60 | 19.6 | 43305 | 2025-09-22 02:13:22 | MASTER-OAFA | (19h 53m 08.47s , -17d 52m 34.7s) | C | 60 | 19.7 | 43381 | 2025-09-22 02:14:38 | MASTER-OAFA | (20h 01m 37.51s , -17d 52m 26.1s) | C | 60 | 19.9 | 43457 | 2025-09-22 02:15:54 | MASTER-OAFA | (19h 53m 11.41s , -17d 50m 53.1s) | C | 60 | 19.7 | 43532 | 2025-09-22 02:17:09 | MASTER-OAFA | (20h 01m 35.40s , -17d 52m 38.4s) | C | 60 | 19.9 | 43608 | 2025-09-22 02:18:25 | MASTER-OAFA | (19h 53m 15.09s , -17d 50m 57.3s) | C | 60 | 19.8 | 43692 | 2025-09-22 02:19:49 | MASTER-OAFA | (21h 04m 54.78s , -14d 06m 56.2s) | C | 60 | 20.2 | 43767 | 2025-09-22 02:21:05 | MASTER-OAFA | (21h 13m 04.77s , -14d 08m 17.9s) | C | 60 | 20.0 | 43843 | 2025-09-22 02:22:20 | MASTER-OAFA | (21h 04m 55.21s , -14d 07m 38.0s) | C | 60 | 20.1 | 43920 | 2025-09-22 02:23:37 | MASTER-OAFA | (21h 13m 07.40s , -14d 06m 29.2s) | C | 60 | 20.0 | 43996 | 2025-09-22 02:24:53 | MASTER-OAFA | (21h 04m 52.78s , -14d 07m 39.7s) | C | 60 | 20.1 | 44074 | 2025-09-22 02:26:12 | MASTER-OAFA | (21h 11m 50.89s , -23d 36m 50.4s) | C | 60 | 20.2 | 44150 | 2025-09-22 02:27:27 | MASTER-OAFA | (21h 20m 32.85s , -23d 36m 14.1s) | C | 60 | 20.1 | 44226 | 2025-09-22 02:28:44 | MASTER-OAFA | (21h 11m 57.12s , -23d 36m 47.6s) | C | 60 | 20.1 | 44302 | 2025-09-22 02:30:00 | MASTER-OAFA | (21h 20m 33.70s , -23d 38m 10.5s) | C | 60 | 20.1 | 44377 | 2025-09-22 02:31:15 | MASTER-OAFA | (21h 11m 56.17s , -23d 37m 33.3s) | C | 60 | 20.1 | 45719 | 2025-09-22 02:53:36 | MASTER-OAFA | (21h 41m 12.76s , -29d 09m 13.2s) | C | 60 | 20.2 | 45873 | 2025-09-22 02:56:10 | MASTER-OAFA | (21h 41m 10.27s , -29d 08m 40.6s) | C | 60 | 20.3 | 46022 | 2025-09-22 02:58:40 | MASTER-OAFA | (21h 41m 16.52s , -29d 08m 42.0s) | C | 60 | 20.3 | 49433 | 2025-09-22 03:55:30 | MASTER-OAFA | (21h 20m 37.25s , -23d 35m 53.7s) | C | 60 | 20.1 | 49589 | 2025-09-22 03:58:07 | MASTER-OAFA | (21h 20m 36.58s , -23d 36m 52.5s) | C | 60 | 20.0 | 49744 | 2025-09-22 04:00:42 | MASTER-OAFA | (21h 20m 40.36s , -23d 35m 16.2s) | C | 60 | 20.1 | 49907 | 2025-09-22 04:03:24 | MASTER-OAFA | (21h 41m 27.25s , -29d 17m 23.8s) | C | 60 | 20.2 | 49982 | 2025-09-22 04:04:39 | MASTER-OAFA | (21h 41m 21.20s , -29d 18m 22.1s) | C | 60 | 20.1 | 50059 | 2025-09-22 04:05:56 | MASTER-OAFA | (21h 41m 20.91s , -29d 17m 20.7s) | C | 60 | 20.2 | 93012 | 2025-09-22 16:01:50 | MASTER-Kislovodsk | (19h 09m 53.50s , +05d 21m 18.7s) | C | 60 | 16.7 | 93012 | 2025-09-22 16:01:50 | MASTER-Kislovodsk | (19h 10m 08.91s , +04d 56m 58.0s) | C | 60 | 16.9 | 96648 | 2025-09-22 17:02:26 | MASTER-Kislovodsk | (19h 11m 04.53s , +05d 11m 24.6s) | C | 60 | 16.9 | 96648 | 2025-09-22 17:02:26 | MASTER-Kislovodsk | (19h 10m 54.81s , +05d 34m 26.2s) | C | 60 | 17.7 | 104034 | 2025-09-22 19:05:31 | MASTER-SAAO | (22h 42m 26.01s , -01d 06m 41.5s) | C | 60 | 19.2 | 104034 | 2025-09-22 19:05:31 | MASTER-SAAO | (22h 40m 35.17s , -00d 51m 17.4s) | C | 60 | 19.3 | 104131 | 2025-09-22 19:07:08 | MASTER-SAAO | (22h 42m 35.06s , +00d 47m 13.4s) | C | 60 | 19.4 | 104131 | 2025-09-22 19:07:08 | MASTER-SAAO | (22h 40m 44.35s , +01d 02m 37.1s) | C | 60 | 19.4 | 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/41945. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40010] GRB 250922B: Fermi GBM Final Real-time Localization
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41944 SUBJECT: GRB 250922B: Fermi GBM Final Real-time Localization DATE: 25/09/22 21:24:08 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 21:13:25 UT on 22 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250922B (trigger 780268410.863384 / 250922884). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 48.7, Dec = 30.7 (J2000 degrees, equivalent to J2000 03h 14m, 30d 41'), with a statistical uncertainty of 13.4 degrees. The angle from the Fermi LAT boresight is 90.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250922884/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250922884/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250922884/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41944. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40009] GRB 250920C: PRIME near-infrared detection
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41943 SUBJECT: GRB 250920C: PRIME near-infrared detection DATE: 25/09/22 20:28:38 GMT FROM: O. Guiffreda at UMD <oriogui(a)umd.edu> O. Guiffreda (UMD), J. Durbak (UMD), A. S. Kutyrev (NASA/GSFC), N. Passaleva (U Rome), M. El Kabir (U Rome), E. Troja (U Rome), S. B. Cenko (NASA/GSFC) Following the Fermi GBM (GCN 41903) and Swift BAT (GCN 41904), we observed the transient field in Z, Y, J and H filters with PRIME ~7 hours after the initial Fermi and Swift detection. At the position of the optical counterpart reported by GOTO (GCN 41907), we detect an uncatalogued source in all aforementioned bands. Using nearby 2MASS and PanSTARRS stars for preliminary calibration we derive the following magnitudes and limits, not corrected for Galactic extinction: |Filter | Mag(AB) | |-------|---------------| |Z | 19.7 +/- 0.10 | |Y | 19.7 +/- 0.07 | |J | 18.8 +/- 0.10 | |H | 18.0 +/- 0.07 | 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/41943. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40008] Konus-Wind detection of GRB 250920B
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41942 SUBJECT: Konus-Wind detection of GRB 250920B DATE: 25/09/22 18:37:52 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 250920B (Fermi-GBM detection: The Fermi GBM team, GCN 41897; Sonawane and Meegan, GCN 41919; Swift-BAT detection: Gupta et al., GCN 41898; Sakamoto et al., GCN 41923; Glowbug detection: Cheung et al., GCN 41937) triggered Konus-Wind at T0=31587.304 s UT (08:46:27.304). The burst light curve shows a multipeaked structure which starts at ~T0-3.0 s and has a total duration of ~141 s. The emission is seen up to ~10 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250920_T31587/ As observed by Konus-Wind, the burst had the total fluence of 3.80(-0.78,+0.93)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+6.368 s, of 6.72(-1.17,+1.16)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+131.328 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.41(-0.10,+0.11), the high energy photon index beta = -2.41(-7.59,+0.35), the peak energy Ep = 310(-69,+94) keV (chi2 = 94/97 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.06(-0.10,+0.10), the high energy photon index beta = -2.33(-0.38,+0.18), the peak energy Ep = 296(-38,+52) keV (chi2 = 87/81 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/41942. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40007] Konus-Wind detection of GRB 250920A
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41941 SUBJECT: Konus-Wind detection of GRB 250920A DATE: 25/09/22 18:33:59 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The bright, long-duration GRB 250920A (Ferm-GBM detection: The Fermi GBM team, GCN 41895; Sonawane and Smith, GCN 41918; BALROG localization: Preis and Greiner, GCN 41896 AstroSat-CZTI detection: Harsha et al., GCN 41899; SVOM-GRM detection: Wang et al., GCN 41912; NuSTAR-detection: Waratkar et al., GCN 41926; IPN triangulation: Kozyrev et al., GCN 41940) triggered Konus-Wind at T0=10444.538 s UT (02:54:04.538). The burst light curve shows a multipeaked structure which starts at ~T0-1.1 s and has a total duration of ~12.5 s. The emission is seen up to ~15 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250920_T10444/ There are no data for the ~18-70 keV band in the triggered mode. As observed by Konus-Wind, the burst had the total fluence of 4.52(-0.15,+0.15)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+1.984 s, of 4.06(-0.28,+0.28)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+18.432 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.84(-0.05,+0.05), the high energy photon index beta = -2.61(-0.09,+0.08), the peak energy Ep = 162(-6,+6) keV (chi2 = 106/97 dof). The spectrum near the maximum count rate (measured from T0+1.792 to T0+2.048 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.58(-0.09,+0.09), the high energy photon index beta = -2.46(-0.14,+0.11), the peak energy Ep = 332(-27,+31) keV (chi2 = 44/46 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/41941. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40006] IPN triangulation of GRB 250920A (long/bright)
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41940 SUBJECT: IPN triangulation of GRB 250920A (long/bright) DATE: 25/09/22 16:39:14 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi GBM team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The bright, long-duration GRB 250920A (Ferm-GBM detection: The Fermi GBM team, GCN 41895; Sonawane and Smith, GCN 41918; BALROG localization: Preis and Greiner, GCN 41896 AstroSat-CZTI detection: Harsha et al., GCN 41899; SVOM-GRM detection: Wang et al., GCN 41912; NuSTAR-detection: Waratkar et al., GCN 41926) was detected by Fermi (GBM trigger 780029651), SVOM (GRM), AstroSat (CZTI), NuSTAR, Konus-Wind, and Mars-Odyssey (HEND), at about 10447 s UT (02:54:07). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 176.909 (11h 47m 38s) +54.466 (+54d 27' 56") Corners: 177.868 (11h 51m 28s) +54.769 (+54d 46' 07") 177.751 (11h 51m 00s) +54.775 (+54d 46' 28") 175.963 (11h 43m 51s) +54.152 (+54d 09' 06") 176.079 (11h 44m 19s) +54.148 (+54d 08' 54") --------------------------------------------- The error box area is 168 sq. arcmin, and its maximum dimension is 1.27 deg (the minimum one is 2.3 arcmin). The Sun distance was 53 deg. This localization may be improved. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB250920_T10444/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/41940. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40005] Konus-Wind detection of GRB 250911A
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41939 SUBJECT: Konus-Wind detection of GRB 250911A DATE: 25/09/22 16:37:08 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 250911A (Swift-BAT detection: Klingler et al., GCN 41781; Palmer et al., GCN 41812; GECAM-B detection: Zhang et al., GCN 41813; Insight-HXMT detection: Wang et al., GCN 41827) triggered Konus-Wind at T0=05370.240 s UT (01:29:30.240). The burst light curve shows a multipeaked structure which starts at ~T0-2.3 s and has a total duration of ~57 s. The weak precursor that triggered Swift-BAT is seen at ~T0-100 s. The emission is seen up to ~10 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250911_T05370/ As observed by Konus-Wind, the burst had the total fluence of 4.54(-0.29,+0.30)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+1.440 s, of 5.15(-0.88,+0.90)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+41.216 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.85(-0.11,+0.12), the high energy photon index beta = -2.58(-0.19,+0.14), the peak energy Ep = 196(-13,+14) keV (chi2 = 102/97 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.92(-0.11,+0.12), the high energy photon index beta = -2.44(-0.19,+0.14), the peak energy Ep = 257(-25,+26) keV (chi2 = 88/84 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/41939. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40004] GRB 250916A: Swift/UVOT Detection
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41938 SUBJECT: GRB 250916A: Swift/UVOT Detection DATE: 25/09/22 15:32:00 GMT FROM: Alice Breeveld at MSSL-UCL <a.breeveld(a)ucl.ac.uk> A. A. Breeveld (UCL-MSSL) and R. Caputo (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of the Fermi/GBM detected burst GRB 250916A 102120s after the trigger (Fermi GBM team, GCN Circ. 41839). The optical counterpart detected by Belkin et al., GCN Circ. 41847; Mohan et al., GCN Circ. 41858; Moskvitin et al., GCN Circ. 41859; Burkhonov et al., GCN Circ. 41860; de Ugarte Postigo et al., GCN Circ. 41863; Moskvitin et al., GCN Circ. 41870; Zheng and Filippenko, GCN Circ. 41873; Pankov et al., GCN Circ. 41892; Hall et al., GCN Circ. 41921 and Moskvitin et al., GCN Circ. 41934, is detected in the initial white and u-band UVOT exposures. Preliminary magnitudes and upper limit using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u 102120 107275 968 20.5 ± 0.2 white 102446 102767 316 21.1 ± 0.3 v 102774 103051 273 >19.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.051 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41938. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40003] GRB 250920B: Glowbug gamma-ray detection
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41937 SUBJECT: GRB 250920B: Glowbug gamma-ray detection DATE: 25/09/22 14:59:17 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 250920B, which was also detected by Fermi/GBM (GCN 41897, 41919) and Swift/BAT (GCN 41898, 41923). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-09-20 08:46:28.344 with a duration of 129.5 s and a total significance of over 30 sigma. The observed light curve comprises an initial multi-peaked structure from ~T0 to T0+7.5s, followed by peaks at ~T0+76s, ~T0+107s, and ~T0+128s. 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/41937. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40002] GRB 250916A: CrAO ZTSh R-band optical observations
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41936 SUBJECT: GRB 250916A: CrAO ZTSh R-band optical observations DATE: 25/09/22 11:24:20 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), V. Rumyantsev (CrAO) report on behalf of IKI-GRB-FuN. We observed the field of the GRB 250916A (The Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855; Osborne et al., GCN 41862; Waratkar and Grefenstette, GCN 41871; Godwin and Meegan, GCN 41876) with the Shajn 2.65m telescope of CrAO, equipped with CCD-photometer. The observations in the R-filter were carried out on epochs 2025-09-19, 2025-09-20, and 2025-09-21. The OT (Belkin et al., GCN 41847; Mohan et al., GCN 41858; Burkhonov et al., GCN 41860; de Ugarte Postigo et al., GCN 41863; Moskvitin et al., GCN 41870; Zheng and Filippenko, GCN 41873; Pankov et al., GCN 41892; Hall et al., GCN 41921; Moskvitin et. al, GCN 41934) is clearly detected in the stacked images taken on each epoch. Preliminary results of our observations are given below: Date UT start t-T0 Exp. Filter OT Err. UL (mid, days) (n*s) (3sigma) 2025-09-19 21:40:39 3.42451 120*120 R 21.45 0.02 25.0 2025-09-20 23:47:56 4.48374 78*120 R 21.89 0.03 24.7 2025-09-21 22:21:48 5.44545 109*120 R 22.72 0.05 24.8 Preliminary photometry is based on the nearby objects from PanSTARRS (magnitudes converted via Lupton 2005 transformations) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41936. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40001] GRB 250920C: Swift-XRT refined Analysis
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41935 SUBJECT: GRB 250920C: Swift-XRT refined Analysis DATE: 25/09/22 10:15:36 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 5.1 ks of XRT data for GRB 250920C, from 110 s to 131.0 ks after the trigger. The data comprise 64 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+7.1 ks) can be modelled with a power-law decay with a decay index of alpha=1.53 (+/-0.09). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.94 (+/-0.10). The best-fitting absorption column is 4.8 (+2.1, -2.0) x 10^20 cm^-2, in excess of the Galactic value of 1.4 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.89 (+0.16, -0.15) and a best-fitting absorption column of 6.7 (+4.0, -3.5) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 6.7 (+4.0, -3.5) x 10^20 cm^-2 Galactic foreground: 1.4 x 10^20 cm^-2 Excess significance: 2.5 sigma Photon index: 1.89 (+0.16, -0.15) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01351039. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41935. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40000] GRB 250916A: SAO RAS Zeiss-1000 optical observations
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41934 SUBJECT: GRB 250916A: SAO RAS Zeiss-1000 optical observations DATE: 25/09/22 09:39:39 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova (SAO), N. Pankov (HSE), A. Pozanenko (IKI), A. Ghosh, S. Razzaque (CAPP, University of Johannesburg), Tao An and Yuanqi Liu (Shanghai Astronomical Observatory) report on behalf of GRB follow-up collaboration and IKI-GRB-FuN. We observed the field of the GRB 250916A (Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855; Osborne et al., GCN 41862; Waratkar and Grefenstette, GCN 41871; Godwin and Meegan, GCN 41876) with the 1-m SAO RAS telescope Zeiss-1000 equipped with the CCD-photometer. We obtained 9 x 300 sec. images Rc band on September 21, 23:36:57 -- September 22, 00:47:22 UT (t_mid - T0 = 5.44639 days). The optical transient (Belkin et al., GCN 41847; Mohan et al., GCN 41858; Moskvitin et al., GCN 41859; Burkhonov et al., GCN 41860; de Ugarte Postigo et al., GCN 41863; Moskvitin et al., GCN 41870; Zheng and Filippenko, GCN 41873; Pankov et al., GCN 41892; Hall et al., GCN 41921) is clearly detected in the stacked frame with the brightness of R = 22.6 +/- 0.1. Date UT start t-T0 Exp. Filter OT Err. UL (3sigma) (mid, d) (s) 2025.09.21 23:36:57 5.44639 9 x 300 Rc 22.6 +/- 0.1 23.3 Preliminary photometry is based on the nearby objects from PanSTARRS (magnitudes converted with Lupton 2005 equations) and has not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41934. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39999] GRB 250921A: Fermi GBM Final Localization
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41933 SUBJECT: GRB 250921A: Fermi GBM Final Localization DATE: 25/09/22 04:52:19 GMT FROM: rhamburg(a)usra.edu The Fermi GBM team reports the detection of a likely LONG GRB "At 03:07:21.46 UT on 22 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250921A (trigger 780203246/250922130). This trigger was initially classified as Below Horizon by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 353.54, Dec = 0.42 (J2000 degrees, equivalent to J2000 23h 34m, +0d 25'), with a statistical uncertainty of 6.13 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/bn250922130/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250922130/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250922130/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41933. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39998] GRB 250920B: Asiago optical observations
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41932 SUBJECT: GRB 250920B: Asiago optical observations DATE: 25/09/21 17:57:22 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> A. Reguitti (INAF/OAPd), L. Tomasella (INAF/OAPd), D. B. Malesani (DAWN/NBI and Radboud) report on behalf of a larger collaboration: We observed the field of GRB 250920B (Gupta et al., GCN 41898; Sonawane & Meegan, GCN 41919) using the 67/92 Schmidt Telescope located at the Asiago observatory (Italy). Observations were carried out using a clear filter, which covers roughly the r and i bands. The optical counterpart (Gupta et al., GCN 41898; Wu et al., GCN 41908; Hall et al., GCN 41914; Kuin & Gupta, GCN 41915) is well detected in our frames. At a mean epoch 2025 Sep 20.771 UT (9.74 hr after the GRB), we measure an AB magnitude r = 18.62 +- 0.06 (calibrated directly against r-band magnitudes from the Pan-STARRS catalog). Considering the filter difference, our measurement is consistent with the nearly simultaneous observation by Hall et al. (GCN 41914). View this GCN Circular online at https://gcn.nasa.gov/circulars/41932. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39997] GRB 250920B: Kitab-ISON optical upper limit
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41931 SUBJECT: GRB 250920B: Kitab-ISON optical upper limit DATE: 25/09/21 17:38:23 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Novichonok (Petrozavodsk State University, KIAM) report on behalf of GRB-IKI-FuN: We observed the field of a long GRB 250920B detected by Fermi/GBM (The Fermi GBM team GCN 41897), Swift (Gupta et. al, GCN 41898), with the RC-36 telescope of Kitab-ISON. The series of unfiltered 325x15 sec exposures was obtained starting on 2025-09-20 at 14:31 UT, i.e. ~0.26 days since Fermi/GBM trigger. The optical afterglow initially detected by Swift/UVOT (Gupta et. al, GCN 41898) and further observed by (WU et. al, GCN 41908; Hall et. al, GCN 41914) is not visible in our stacked image of 298x15 sec. Preliminary results of our observations provided below: Date UTstart Exptime t-T0 Filter OT Err. UL (nxs) (mid, days) (3sigma) 2025-09-20 14:31:30 298x15 0.26550 Clear n/d n/d 15.4 The photometry was calibrated against nearby USNO-B1.0 stars (R2 mags) and not corrected for the Galactic extinction. Ref. stars USNO-B1.0 RA Dec R2 187.73536 47.71878 13.75 187.52490 47.74643 13.74 View this GCN Circular online at https://gcn.nasa.gov/circulars/41931. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39996] GRB 250917B: Mondy and Zeiss-1000 SAO RAS optical observations, optical observations, afterglow candidate
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41930 SUBJECT: GRB 250917B: Mondy and Zeiss-1000 SAO RAS optical observations, optical observations, afterglow candidate DATE: 25/09/21 13:38:53 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> N. Pankov (HSE), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), E. Klunko (ISTP), O. Spiridonova (SAO RAS) report on behalf of GRB IKI FuN: We observed the field of Swift XRT of GRB 250917B (Fermi GBM team GCN 41846; Caputo et al. GCN 41848 ) with AZT-33IK telescope of Mondy observatory in R-filter on 2025-09-17 starting (UT) 13:36:18(epoch 1) and Zeiss-1000 of SAO RAS starting on 2025-09-17 (UT) 16:24:04 (epoch 2). We do not detect any new sources within S1, S5, S6 XRT localisation (Kennea et al., GCN 41851). This is consistent with optical observations (Hu et al, GCN 41854; Breeveld et al, GCN 41864; Yadav et al., GCN 41872; Zheng et al., GCN 41927). However, at the boundary of the S5 XRT circle, we found an object (coordinates are (J2000) 19:25:33.74 +11:04:24.85) that was significantly brighter in epoch 1 compared to epoch 2. The photometry of the object is the following Date UT start t-T0 Filter OT Err. UL(3sigma) Telescope (mid, days) (s) 2025-09-17 13:36:18 0.31845 R 19.97 +/- 0.08 21.4 AZT-33IK 2025-09-17 16:24:04 0.42394 Rc 20.79 +/- 0.12 21.3 Zeiss-1000 We suggest the source is an afterglow candidate of GRB 250917B. The object is a diffuse one and most likely is the galaxy. View this GCN Circular online at https://gcn.nasa.gov/circulars/41930. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39995] GRB 250920C: SVOM/GRM observation
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41929 SUBJECT: GRB 250920C: SVOM/GRM observation DATE: 25/09/21 12:22:56 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang. Wen-Jun Tan, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP), Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 250920C (SVOM trigger reference: sb25092008) at 2025-09-20T15:25:17.400 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41895) and Swift/BAT (R. Gupta, GCN#41904). 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 39.5 +0.5/-1.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250920C.png In addition, the position of this burst, as determined by Swift/BAT (RA= 51.459, DEC= -29.646, GCN#41904), is located at about 81 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, but this burst is still detected by ECLAIRs through the shield. With this localization, the time-averaged spectrum from T0-2 to T0+41 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.08 +0.08/-0.08 and the cutoff energy, parameterized as Epeak, is 166 +19/-15 keV. The event fluence (10-1000 keV) in this time interval is (3.36 +0.17/-0.16)E-05 erg/cm^2. With the redshift of z=1.40 (R. Sanchez-Ramirez et al., GCN#41928), the localization of GRB 250920C in the 'Amati' relation diagram is consistent with type II GRBs, as shown at: https://www.bursthub.cn//admin/static/svgrb250920C_amati.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41929. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39994] GRB 250920C: GTC/OSIRIS+ spectroscopic redshift z = 1.40
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41928 SUBJECT: GRB 250920C: GTC/OSIRIS+ spectroscopic redshift z = 1.40 DATE: 25/09/21 09:47:37 GMT FROM: Ruben Sanchez-Ramirez at IAA-CSIC <ruben(a)iaa.es> R. Sanchez-Ramirez, A. J. Castro-Tirado, S. Guziy, M.D. Caballero-Garcia, S.-Y. Wu and I. Perez-Garcia (IAA-CSIC), A. M. Garcia-Rodríguez (GTC, IAC), A. Tejero-Caro (GTC), S. B. Pandey (ARIES), M. Gritsevich (Univ. of Helsinki), Y.-D. Hu (GXI), A. Nicuesa Guelbenzu (Tautenburg Obs.), L. Piro (INAF/IAPS) and B.-B. Zhang (NJU), on behalf of a larger collaboration, report: Following the detection of GRB 250920C by Fermi (Fermi Team, GCN 41903; Mailyan et al. GCN 41907), Swift (Gupta et al. GCN 41904, 41924), we observed the optical afterglow (Wortley et al. GCN 41907, Strausbaugh et al. GCN 41911, Ghosh et al. GCN 41913, Kuin et al. GCN 41920, Mohan et al. GCN 41925) with the 10.4m GTC telescope, at the Spanish Roque de los Muchachos Observatory, on the island of La Palma, equipped with the OSIRIS+ instrument. The spectroscopic observations were performed at a high airmass and consisted of 3x900s exposures using grism R1000B, with a spectral coverage between 3,600 and 7,700 A and a resolving power of ~600. The observations started on Sep 21, 04:29 UT (i.e. 13.07 h after the burst trigger). From a preliminary reduction, we find a low SNR continuum over all the wavelength range but the bluest extreme, most probably due to atmospheric extinction. The extracted spectrum shows several absorption features that we interpret as AlII, AlIII, ZnII, FeII, MgII, and MgI at z=1.40, which we propose as the redshift of GRB 250920C. View this GCN Circular online at https://gcn.nasa.gov/circulars/41928. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39993] GRB 250917B: KAIT optical upper limit
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41927 SUBJECT: GRB 250917B: KAIT optical upper limit DATE: 25/09/21 08:31:40 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, automatically responded to the Swift triggered GRB 250917B (Caputo et al., GCN 41848; see also Fermi GBM Team, GCN 41846) starting at 06:29:01 UT, 77 seconds after the burst. A set of 10x20s, 10x40s and 50x60s clear (roughly R) filter images were obtained. We do not detect any new uncataloged source around Swift-XRT sources 1, 5 or 6 (Kennea et al., GCN 41851) neither in single image nor in coadd images. We estimate the limiting mag of ~21.5 (Vega) at a mid time of 45 minutes after the burst in our coadd image. View this GCN Circular online at https://gcn.nasa.gov/circulars/41927. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39992] GRB 250920A: NuSTAR detection of bright prompt emission
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41926 SUBJECT: GRB 250920A: NuSTAR detection of bright prompt emission DATE: 25/09/21 06:06:22 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 250920A in both the NuSTAR CsI anti-coincidence shields. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm triggered at 2025-09-20T02:54:07.000 (with a resolution ~5-seconds). This is consistent with the detections of GRB 250920A by Fermi/GBM (Fermi GBM Team, GCN Circ. 41895, Sonawane et al., GCN Circ. 41918), AstroSat/CZTI (Harsha et al., GCN Circ. 41898), and SVOM/GRM (Wang et al., GCN Circ. 41912). The NuSTAR CsI shield data are recorded at 1 Hz. The burst appears to be composed of one bright peak lasting for ~4-s, followed by a relatively fainter peak lasting for 3-s. The peak count rate is ~5000-cps over a baseline rate of ~1,000-cps during this time period. We also see clear evidence in the signal above 100 keV in the CdZnTe detectors for the first episode. The Fermi/GBM localization (Fermi GBM Team, GCN Circ. 41895) at RA = 175.27, Dec = 48.96 implies an offset from the NuSTAR boresight of 104-deg (i.e., through the side of the instrument) and an offset from the geocenter of 94-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250920A Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/41926. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39991] GRB 250920C: GROWTH-India Telescope optical observations
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41925 SUBJECT: GRB 250920C: GROWTH-India Telescope optical observations DATE: 25/09/21 05:57:11 GMT FROM: Varun Bhalerao at IIT Bombay <varunb(a)iitb.ac.in> GRB 250920C: GROWTH-India Telescope optical observations T. Mohan, V. Swain, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of Swift GRB 250920C (Gupta et al., 41904), also detected by Fermi/GBM (GBM Team, GCN 41903) with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-09-20 20:17:41 UT, i.e., 4.87 hours after the Fermi trigger. We obtained multiple exposures in g', r', and i' filters. We detect the optical afterglow in our stacked image at position reported by Wortley et al., GCN 41907. The photometry result follows as: | MJD (mid) | tmid - t0 (hours) | Filter | Exposure (s) | Magnitude (AB) | | ----------- | ----------------- | ------ | ------------ | -------------- | | 60938.85555 | 5.11 | r' | 3*360 | 19.52+-0.1 | | 60938.85836 | 5.18 | i' | 2*360 | 19.22+-0.1 | | 60938.91480 | 6.53 | g' | 2*360 | 19.88+-0.12 | | 60938.94269 | 7.22 | i' | 5*360 | 19.71+-0.12 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our magnitude is consistent with other optical observations (Wortley et al., GCN 41907, Strausbaugh et al., GCN 41911, Ghosh et al., GCN 41913, Lipunov et al., GCN 41916, Kuin et al., GCN 41920). The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/41925. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39989] GRB 250920C: Swift-BAT refined analysis
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41924 SUBJECT: GRB 250920C: Swift-BAT refined analysis DATE: 25/09/21 02:16:24 GMT FROM: Rahul Gupta at NASA GSFC <rahul.gupta(a)nasa.gov> R. Gupta (GSFC), S. D. Barthelmy (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+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250920C (trigger #1351039) (R. Gupta, et al., GCN Circ. 41904). The BAT ground-calculated position is RA, Dec = 51.465, -29.646 deg which is RA(J2000) = 03h 25m 51.6s Dec(J2000) = -29d 38' 46.7" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 15%. The BAT mask-weighted light curve exhibits a bright initial peak followed by multiple structured emission episodes, lasting for about 40 sec from the trigger time. T90 (15-350 keV) is 38.02 +- 1.27 sec (estimated error including systematics). The time-averaged spectrum from T-0.44 to T+40.49 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.09 +- 0.18, and Epeak of 133.4 +- 43.9 keV (chi squared 45.87 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 1.3 +- 0.0 x 10^-05 erg/cm2 and the 1-sec peak flux measured from T-0.12 sec in the 15-150 keV band is 16.9 +- 1.0 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.48 +- 0.04 (chi squared 60.21 for 57 d.o.f.). 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/1351039 View this GCN Circular online at https://gcn.nasa.gov/circulars/41924. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39990] GRB 250920B: Swift-BAT refined analysis
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41923 SUBJECT: GRB 250920B: Swift-BAT refined analysis DATE: 25/09/21 02:14:23 GMT FROM: Rahul Gupta at NASA GSFC <rahul.gupta(a)nasa.gov> T. Sakamoto (AGU), 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), (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250920B (trigger #1351008) (R. Gupta, et al., GCN Circ. 41898). The BAT ground-calculated position is RA, Dec = 187.316, 47.843 deg which is RA(J2000) = 12h 29m 15.8s Dec(J2000) = +47d 50' 33.6" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 57%. The BAT mask-weighted light curve shows multiple emission episodes extending over ~150 sec. T90 (15-350 keV) is 128.44 +- 1.00 sec (estimated error including systematics). The time-averaged spectrum from T-4.83 to T+149.43 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.31 +- 0.15, and Epeak of 182.2 +- 153.0 keV (chi squared 36.64 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 1.1 +- 0.0 x 10^-05 erg/cm2 and the 1-sec peak flux measured from T+0.29 sec in the 15-150 keV band is 5.0 +- 0.3 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.52 +- 0.04 (chi squared 42.79 for 57 d.o.f.). 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/1351008 View this GCN Circular online at https://gcn.nasa.gov/circulars/41923. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39988] GRB 250920C: Enhanced Swift-XRT position
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41922 SUBJECT: GRB 250920C: Enhanced Swift-XRT position DATE: 25/09/20 22:43:41 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 915 s of XRT Photon Counting mode data and 3 UVOT images for GRB 250920C, 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 = 51.46554, -29.65537 which is equivalent to: RA (J2000): 03h 25m 51.73s Dec (J2000): -29d 39' 19.3" with an uncertainty of 2.2 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/41922. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39987] GRB 250916A: FTW optical and NIR observations of the counterpart
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41921 SUBJECT: GRB 250916A: FTW optical and NIR observations of the counterpart DATE: 25/09/20 22:03:31 GMT FROM: Xander J Hall at Carnegie Mellon University <xjh(a)andrew.cmu.edu> Xander J. Hall (Carnegie Mellon U.), Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report: We observed the counterpart of GRB 250916A (Fermi GBM Team, GCN 41839; Belkin et al., GCN 41847) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 5 x 180 s starting at 2025-09-19 23:23:41 UT (3.4 days after the trigger). We detect the counterpart clearly in all filters and report the following magnitude: r = (21.75 +/- 0.06) mag. The magnitude is calibrated against the PS1 catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction. We thank Christoph Ries from the Wendelstein Observatory for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41921. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39986] GRB 250920C: Swift/UVOT Detection
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41920 SUBJECT: GRB 250920C: Swift/UVOT Detection DATE: 25/09/20 21:48:29 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> N. P. M. Kuin (UCL-MSSL) and R. Gupta (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250920C 124 s after the BAT trigger (Gupta et al., GCN Circ. 41904). A source consistent with the XRT position is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000)= 03h 25m 51.76s, 51.46568 deg Dec (J2000) = -29d 39m 20.2s, -29.65562 deg consistent with the detection by GOTO (Wortley et al. GCN Circ. 41907). 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 146 207 60.5 14.55 +/- 0.04 v 124 133 10.1 14.56 +/- 0.09 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.019 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41920. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39985] GRB 250920B: Fermi GBM Observation
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41919 SUBJECT: GRB 250920B: Fermi GBM Observation DATE: 25/09/20 21:03:38 GMT FROM: Rushikesh Digambar Sonawane PHD231014 at IISER, TVM <rushikesh23(a)iisertvm.ac.in> R. Sonawane (IISER, TVM) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 08:46:26.16 UT on 20 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250920B (trigger 780050791/250920366). which was also detected by Swift BAT (R. Gupta et al. 2025, GCN 41898), SVOM C-GFT (WU et al. 2025, GCN 41908), and Swift UVOT (Kuin et al. 2025, GCN 41915) . The Fermi GBM Final Real-time localization (GCN 41897) is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 56 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 127.7 s (50-300 keV). The time-averaged spectrum from T0-3.6 to T0+141.8 s is best fit by a Band function with Epeak = 118 +/- 7 keV, alpha = -0.85 +/- 0.05, and beta = -2.09 +/- 0.05. The event fluence (10-1000 keV) in this time interval is (3.33 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+9.4 s in the 10-1000 keV band is 8.8 +/- 0.3 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/41919. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39984] GRB 250920A: Fermi GBM Detection
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41918 SUBJECT: GRB 250920A: Fermi GBM Detection DATE: 25/09/20 21:01:18 GMT FROM: Rushikesh Digambar Sonawane PHD231014 at IISER, TVM <rushikesh23(a)iisertvm.ac.in> R. Sonawane (IISER, TVM) and J.R. Smith (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 02:54:06.82 UT on 20 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250920A (trigger 780029651/250920121). which was also detected by AstroSat-CZTI( Harsha K. H. et al. 2025, GCN 41899), and SVOM-GRM (Chen-Wei Wang et al. 2025, GCN 41912). The Fermi GBM Final Localization is presented in GCN 41895. The angle from the Fermi LAT boresight is 88 degrees. The GBM light curve consists of two emission episodes with a duration (T90) of about 9.4 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+13.312 s is best fit by a Band function with Epeak = 151 +/- 3 keV, alpha = -0.81 +/- 0.02, and beta = -2.39 +/- 0.04. The event fluence (10-1000 keV) in this time interval is (4.22 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.7 s in the 10-1000 keV band is 102.5 +/- 0.7 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/41918. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39983] GRB 250920C: Fermi GBM Observation
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41917 SUBJECT: GRB 250920C: Fermi GBM Observation DATE: 25/09/20 20:46:55 GMT FROM: Bagrat Mailyan at Florida Tech <mbagrat(a)gmail.com> B. Mailyan (Florida Tech) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 15:25:17.06 UT on 20 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250920C (trigger 780074722/250920643) which was also detected by Swift BAT (R. Gupta et al. 2025, GCN 41904). The Fermi GBM Final Real-time Localization (GCN 41903) is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 94 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 36.6 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+37.377 s is best fit by a Band function with Epeak = 117 +/- 4 keV, alpha = -0.76 +/- 0.04, and beta = -2.34 +/- 0.05. The event fluence (10-1000 keV) in this time interval is (2.97 +/- 0.04)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+26 s in the 10-1000 keV band is 25.1 +/- 0.5 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/41917. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39982] Swift GRB 250920C: Global MASTER-Net observations report
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41916 SUBJECT: Swift GRB 250920C: Global MASTER-Net observations report DATE: 25/09/20 19:34:22 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 250920C ( R. Gupta et al., GCN 41904) errorbox 13198 sec after notice time and 13225 sec after trigger time at 2025-09-20 19:05:42 UT, with upper limit up to 18.1 mag. The observations began at zenith distance = 85 deg. The sun altitude is -32.4 deg. The galactic latitude b = -56 deg., longitude l = 226 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2996190 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 13315 | MASTER-SAAO | C | 180 | 14.4 | 14583 | MASTER-SAAO | C | 180 | 15.6 | 14583 | MASTER-SAAO | C | 180 | 18.1 | 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/41916. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39981] GRB 250920B: Swift/UVOT Detection
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41915 SUBJECT: GRB 250920B: Swift/UVOT Detection DATE: 25/09/20 19:22:10 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> Paul Kuin (MSSL) and Rahul Gupta (NASA GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250920B 99 s after the BAT trigger (Gupta et al., GCN Circ. 41898). A source consistent with the XRT position (Evans et al. GCN. Circ. 41910) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 12:29:16.07 = 187.31697 (deg.) Dec (J2000) = +47:50:14.4 = 47.83732 (deg.) with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 99 249 147 13.89 +/- 0.02 v 4433 4633 197 16.53 +/- 0.05 b 3818 4018 197 16.62 +/- 0.04 u 311 452 139 13.26 +/- 0.02 w1 4843 5043 197 17.02 +/- 0.08 m2 4638 4838 197 >19.2 w2 4228 4428 197 19.21 +/- 0.25 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.011 in the direction of the burst (Schlegel et al. 1998). The observation also included a 49s long UV grism exposure. Inspection of the noisy grism spectrum suggests a redshift of 2.2 based on identifying an broad absorption with the the Ly-alpha line. View this GCN Circular online at https://gcn.nasa.gov/circulars/41915. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39980] GRB 250920B: FTW optical and NIR observations of the counterpart
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41914 SUBJECT: GRB 250920B: FTW optical and NIR observations of the counterpart DATE: 25/09/20 19:17:41 GMT FROM: Xander J Hall at Carnegie Mellon University <xjh(a)andrew.cmu.edu> Xander J Hall (Carnegie Mellon U.), Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report: We observed the counterpart of GRB 250920B (Fermi GBM Team, GCN 41897; Gupta et al., GCN 41898; Wu et al., GCN 41908) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 10 x 60s starting at 2025-09-20 18:19:54 UT (0.4 days after the trigger). We detect the counterpart clearly in all filters and report the following magnitude: r = (18.81 +/- 0.01) mag. The magnitude is calibrated against the PS1 catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction. We thank Christoph Ries and Ralf Bender from the Wendelstein Observatory for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41914. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39979] GRB 250920C: Optical counterpart detection by LCO
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41913 SUBJECT: GRB 250920C: Optical counterpart detection by LCO DATE: 25/09/20 18:32:10 GMT FROM: ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994(a)gmail.com> Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration. We observed the field of the GRB 250920C triggered by the Swift (Gupta et al., GCN 41904) in the r, V filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Siding Spring is near Coonabarabran, New South Wales, Australia . The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel). Observations began on September 20, 2025, starting 1.47 hours after the GRB trigger. Further observations are currently ongoing. We clearly detect the optical transient (OT) reported by GCNs (Wortley et al., GCN 41907, Strausbaugh et al., GCN 41911) in our r and V band image. |Date| |JDstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ---------------------------------------------------------------------------------------------------- 2025-09-20 2460939.20389 1.47 1 x 600 r r = 18.47 +/- 0.01 2025-09-20 2460939.22762 2.04 1 x 600 r r = 18.75 +/- 0.01 The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41913. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39978] GRB 250920A: SVOM/GRM observation
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41912 SUBJECT: GRB 250920A: SVOM/GRM observation DATE: 25/09/20 18:19:32 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang. Wen-Jun Tan, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a bright burst GRB 250920A (SVOM trigger reference: sb25092001) at 2025-09-20T02:54:09.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41895) and AstroSat (Harsha K. H., GCN#41899). 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 9.6 +0.3/-0.1 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250920A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 175.27, DEC= 48.96, GCN#41895), is located at about 144 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, but this burst still clearly detected by ECLAIRs through the shield. With this localization, the time-averaged spectrum from T0-3 to T0+11 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.58 +0.06/-0.06 and the cutoff energy, parameterized as Epeak, is 202 +17/-13 keV. The event fluence (10-1000 keV) in this time interval is (6.24 +0.14/-0.13)E-05 erg/cm^2. The localization of GRB 250919A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb250920A_amati.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41912. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39977] GRB250920C: LCOGT Optical Detection
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41911 SUBJECT: GRB250920C: LCOGT Optical Detection DATE: 25/09/20 17:10:36 GMT FROM: Robert Strausbaugh at Eastern Illinois University <rstrausbaugh(a)eiu.edu> R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the Swift GRB 250920C field (Gupta et al., GCN 41904) with the LCOGT 1-meter Sinistro instrument at the Siding Spring Observatory, Australia site, on September 20, from 16:29 to 16:51 UT (corresponding to 1.07 to 1.26 hours after the GRB trigger time) with the SDSS r and i filters. We performed a series of 3x200s exposures in i-band and r-band. We detect an uncatalogued source consistent with GOTO optical counterpart candidate (Wortley et al., GCN 41907) in both bands. The following magnitudes are calculated using the PanSTARRS catalog as reference: r = 18.54 +/- 0.05 i = 18.25 +/- 0.01 These magnitudes are not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41911. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39976] GRB 250920B: Enhanced Swift-XRT position
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41910 SUBJECT: GRB 250920B: Enhanced Swift-XRT position DATE: 25/09/20 17:03:19 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 1850 s of XRT Photon Counting mode data and 5 UVOT images for GRB 250920B, 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 = 187.31688, +47.83750 which is equivalent to: RA (J2000): 12h 29m 16.05s Dec (J2000): +47d 50' 15.0" with an uncertainty of 1.9 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/41910. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39975] GRB 250920B: Swift-XRT refined Analysis
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41909 SUBJECT: GRB 250920B: Swift-XRT refined Analysis DATE: 25/09/20 16:55:32 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> K.L. Page (U. Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (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 250920B, from 87 s to 22.3 ks after the trigger. The data comprise 395 s in Windowed Timing (WT) mode (the first 2 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The refined XRT position is RA, Dec = 187.3175, +47.8376 which is equivalent to: RA (J2000): 12h 29m 16.21s Dec(J2000): +47d 50' 15.2" with an uncertainty of 3.5 arcsec (radius, 90% confidence). The late-time light curve (from T0+3.8 ks) can be modelled with a power-law decay with a decay index of alpha=1.20 (+/-0.05). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.490 (+0.035, -0.017). The best-fitting absorption column is consistent with the Galactic value of 1.1 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.89 (+/-0.07) and a best-fitting absorption column of 3.3 (+1.5, -1.4) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (3.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.3 (+1.5, -1.4) x 10^20 cm^-2 Galactic foreground: 1.1 x 10^20 cm^-2 Excess significance: 2.5 sigma Photon index: 1.89 (+/-0.07) If the light curve continues to decay with a power-law decay index of 1.20, the count rate at T+24 hours will be 0.10 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.5 x 10^-12 (3.8 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/01351008. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41909. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39974] GRB 250920B: SVOM/C-GFT optical observations
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41908 SUBJECT: GRB 250920B: SVOM/C-GFT optical observations DATE: 25/09/20 16:38:42 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 250920B detected by Fermi/GBM (Fermi Team, GCN 41897) and Swift/BAT (Gupta et al., GCN 41898) with LATIOS on SVOM/C-GFT. Observations started at 2025-09-20 11:22:32.815 UTC, ~2.60 hr after the trigger. The optical counterpart reported by Gupta et al.(GCN 41898) was clearly detected in our stacked images of band g, r, and i. The magnitudes are: | mid-time (T-T₀) / hr | exposure time / s | band | mag (AB) | mag err | |:---------------------|:------------------|:-----|:---------|:--------| | 2.76 | 10×30 | g | 17.15 | ±0.07 | | 2.64 | 10×30 | r | 17.05 | ±0.07 | | 2.85 | 9×30 | i | 17.01 | ±0.05 | The photometry was calibrated with nearby Pan-STARRS1 stars. Magnitudes were not corrected for dust extinction. We thank the observation assistants Shuai Liu and Chunlei Guo 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/41908. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39973] GRB 250920C: GOTO optical counterpart candidate
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41907 SUBJECT: GRB 250920C: GOTO optical counterpart candidate DATE: 25/09/20 16:16:16 GMT FROM: d.s.oneill(a)bham.ac.uk M. E. Wortley, D. O'Neill, B. P. Gompertz, G. Ramsay, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, A. Kumar, B. Godson, 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 250920C (GCN #41903, Fermi GBM team, #41904, Gupta et al.). Targeted observations were performed at 2025-09-20 15:33:10 (starting 0.13 hours after trigger). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogues. Human vetting was carried out in real time on any candidates that passed the above checks. We identify a candidate optical counterpart GOTO25hju with L = 15.91±0.01 AB mag, within the Swift/BAT error region with coordinates: RA,DEC (J2000) = 51.465773, -29.65547 | 03:25:51.79, -29:39:19.67 We find no evidence of these sources prior to the GRB trigger time in previous GOTO observations taken at 2025-09-17 16:39:05 UT (2.95d pre-trigger) down to a depth of L<19.7 AB mag, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). There is a faint, point-like object coincident at the source location in the Legacy catalogue. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Observations are ongoing. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/41907. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39972] GRB 250919A / EP250919a: LCO optical observation
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41906 SUBJECT: GRB 250919A / EP250919a: LCO optical observation DATE: 25/09/20 16:06:37 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), D. Turpin (CEA/Irfu), J. T. Palmerio (CEA/Irfu), Z. Q. Wang (GXU), Y. F. Liang (PMO), report on behalf of the SVOM mission team: We observed the field of GRB 250919A / EP250919a detected by Fermi/GBM (Fermi GBM Team, GCN 41874), EP/WXT (Liang et al., GCN 41879), SVOM/GRM (Wang et al., GCN 41882), Fermi/LAT (Holzmann Airasca et al., GCN 41884), NuSTAR (Waratkar et al., GCN 41888), Glowbug (Cheung et al., GCN 41891), Insight-HXMT (Wang et al. GCN 41900), Konus-Wind (Frederiks et al. GCN 41905), with the LCO 1m telescope at Siding Spring Observatory equipped with the Sinistro instrument. We obtained 3x200 s exposures in each of the SDSS g, r and i filters. The optical counterpart (Li et al., GCN 41877; Levan et al., GCN 41883; Oates et al., GCN 41886; Lipunov et al., GCN 41893; Ma et al. GCN 41894) is clearly detected in our subtracted image (using the Legacy Survey DR10 image template) with the following magnitudes (calibrated against the SkyMApper DR4 catalogued stars, not corrected for Galactic extinction): g = 19.49 +/- 0.02 (AB), at a mid-time of 32.7 hr after the trigger; r = 19.19 +/- 0.03 (AB), at a mid-time of 32.5 hr after the trigger; i = 18.98 +/- 0.04 (AB), at a mid-time of 32.5 hr after the trigger. Further observations are planned. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/41906. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39971] Konus-Wind detection of GRB 250919A
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41905 SUBJECT: Konus-Wind detection of GRB 250919A DATE: 25/09/20 15:50:37 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long GRB 250919A (Fermi-GBM detection: The Fermi GBM team, GCN 41874; Mukherjee & Meegan, GCN 41890; EP-WXT detection: Liang et al., GCN 41879; SVOM-GRM observaion: Wang et al., GCN 41882), Fermi-LAT detection: Holzmann Airasca et al., GCN 41884; Glowbug detection: Cheung et al., GCN 41891; AstroSat CZTI detection: Harsha et al., GCN 41899) triggered Konus-Wind (KW) at T0=1741.403 s UT (00:29:01.403). The burst consists of two separated emission pulses and had the total duration of ~240 s. The emission is seen up to ~10 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250919_T01741/ As observed by Konus-Wind, the burst had a fluence of (4.24 ± 0.25)x10^-4 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 23.168 s, of (1.33 ± 0.09)x10^-4 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+218 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.94 (-0.05,+0.05), the high energy photon index beta = -2.32 (-0.17,+0.11), the peak energy Ep = 452 (-33,+39) keV, chi2 = 101/97 dof. The spectrum near the peak count rate (measured from T0+23.04 to T0+23.296 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.07 (-0.09,+0.10), the high energy photon index beta = -2.15 (-0.07,+0.06), the peak energy Ep = 515 (-38,+42) keV, chi2 = 63/62 dof. Assuming the redshift z=1.145 (Levan et al., GCN 41883) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the burst isotropic energy release E_iso to (1.53 ± 0.09)x10^54 erg, the isotropic peak luminosity L_iso to (1.03 ± 0.07)x10^54 erg/s, and the rest-frame peak spectral energy Ep,z to (970 ± 80) keV. With the obtained estimates, GRB 250919A is consistent with 68% prediction bands of both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB250919_T01741/GRB250919A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/41905. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39970] GRB 250920C: Swift detection of a burst
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41904 SUBJECT: GRB 250920C: Swift detection of a burst DATE: 25/09/20 15:39:55 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> R. Gupta (NASA GSFC), S. Dichiara (PSU), C. Gronwall (PSU), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 15:25:17 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250920C (trigger=1351039). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 51.459, -29.646 which is RA(J2000) = 03h 25m 50s Dec(J2000) = -29d 38' 44" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 40 sec. The peak count rate was ~8500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 15:27:21.2 UT, 123.8 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 51.4644, -29.6566 which is equivalent to: RA(J2000) = 03h 25m 51.46s Dec(J2000) = -29d 39' 23.8" with an uncertainty of 5.3 arcseconds (radius, 90% containment). This location is 41 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. The initial flux in the 2.5 s image was 1.50e-09 erg cm^-2 s^-1 (0.2-10 keV). There are no UVOT data available at this time. Burst Advocate for this burst is R. Gupta (rahulbhu.c157 AT gmail.com) 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/41904. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39969] GRB 250920C: Fermi GBM Final Real-time Localization
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41903 SUBJECT: GRB 250920C: Fermi GBM Final Real-time Localization DATE: 25/09/20 15:36:01 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 15:25:17 UT on 20 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250920C (trigger 780074722.062672 / 250920643). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 47.6, Dec = -26.7 (J2000 degrees, equivalent to J2000 03h 10m, -26d 41'), with a statistical uncertainty of 1.2 degrees. The angle from the Fermi LAT boresight is 93.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920643/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920643/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920643/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41903. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39968] LIGO/Virgo/KAGRA S250920bq: Coverage and upper limits from MAXI/GSC observations
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41902 SUBJECT: LIGO/Virgo/KAGRA S250920bq: Coverage and upper limits from MAXI/GSC observations DATE: 25/09/20 14:43:37 GMT FROM: Satoshi Sugita at Aoyama Gakuin U. <sugita(a)phys.aoyama.ac.jp> Y. Kawakubo, S. Sugita, M. Serino, H. Hiramatsu, Y. Kondo (AGU) H. Negoro, M. Nakajima, K. Takagi (Nihon U.), N. Kawai, T. Mihara, (RIKEN), report on behalf of the MAXI team: We examined MAXI/GSC all-sky X-ray images (2-20 keV) after compact binary merger candidate S250920bq at 2025-09-20 10:27:39.063 UTC. At the trigger time of S250920bq, the high-voltage of MAXI/GSC was on, but the FOV was out of the 90% credible region of the bayestar skymap. The first one-orbit (92 min) scan observation with GSC after the event covered 100% of the 90% credible region of the bayestar skymap from 10:30:54 to 10:46:39 UTC (T0+195 to T0+1140 sec). No significant new source was found in the region in the one-orbit scan observation. A typical 1-sigma averaged upper limit obtained in one scan observation is 20 mCrab at 2-20 keV. If you require information about X-ray flux by MAXI/GSC at specific coordinates, please contact the submitter of this circular by email. View this GCN Circular online at https://gcn.nasa.gov/circulars/41902. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39967] Swift GRB 250920B: Global MASTER-Net observations report
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41901 SUBJECT: Swift GRB 250920B: Global MASTER-Net observations report DATE: 25/09/20 13:28:21 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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the Swift GRB 250920B ( R. Gupta et al., GCN 41898) errorbox 16004 sec after notice time and 16025 sec after trigger time at 2025-09-20 13:13:36 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 66 deg. The sun altitude is -19.4 deg. The galactic latitude b = 69 deg., longitude l = 132 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2995928 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 16056 | MASTER-Tunka | C | 60 | 19.9 | 16056 | MASTER- | C | 60 | 19.6 | 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/41901. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39966] GRB 250919A / EP250919a: Insight-HXMT detection
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41900 SUBJECT: GRB 250919A / EP250919a: Insight-HXMT detection DATE: 25/09/20 13:01:19 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong, Shi-Jie Zheng, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-09-19T00:29:15.000 (T0), Insight-HXMT/HE detected the burst GRB 250919A, which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41874), SVOM/GRM (Wang et al., GCN#41882), Fermi/LAT (A. Holzmann Airasca, GCN#41884), NuSTAR (G. Waratkar et al., GCN#41888), Glowbug (C.C. Cheung et al., GCN#41891), associated with EP250919a detected by EP/WXT (Liang et al., GCN Circ. 41879). The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 117.0 +4.5/-3.0 s. The 1s peak rate, measured from T0+10.250 s, is 14624 cnts/sec. The total counts from this burst is 98750 counts. However, the HE detector was suffered from saturation from T0+6 s to T0+8 s and T0+10 s to T0+11 s due to the high-brightness. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb250919A.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/41900. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39965] GRB 250920A: AstroSat CZTI detection
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41899 SUBJECT: GRB 250920A: AstroSat CZTI detection DATE: 25/09/20 09:29:54 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), A. Goyal (IITB), A. Arya (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 bright, long GRB 250920A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 41895). 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 2025-09-20 02:54:08.95 UTC. The measured peak count rate associated with the burst is 636 (+45, -50) counts/s above the background in the combined data of two quadrants (out of four), with a total of 1944 (+129, -140) counts. The local mean background count rate was 149 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 9.3 (+0.5, -0.4) 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 2025-09-20 02:54:08.30 UTC. The measured peak count rate associated with the burst is 2813 (+106, -113) counts/s above the background in the combined data of all quadrants, with a total of 4822 (+303, -320) counts. The local mean background count rate was 1366 (+7, -7) counts/s. We measure a T90 of 8.7 (+0.7, -0.4) 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/41899. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39964] GRB 250920B: Swift detection of a burst with a bright optical counterpart.
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41898 SUBJECT: GRB 250920B: Swift detection of a burst with a bright optical counterpart. DATE: 25/09/20 09:01:06 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> R. Gupta (NASA GSFC), C. Gronwall (PSU), N. P. M. Kuin (UCL-MSSL) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 08:46:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250920B (trigger=1351008). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 187.337, +47.844 which is RA(J2000) = 12h 29m 21s Dec(J2000) = +47d 50' 39" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed multiple peaks, with a complex structure with a duration of about 150 sec. The peak count rate was ~8200 counts/sec (15-350 keV), at ~5 sec after the trigger. The XRT began observing the field at 08:48:01.1 UT, 90.6 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 187.3179, 47.8372 which is equivalent to: RA(J2000) = 12h 29m 16.30s Dec(J2000) = +47d 50' 13.9" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 52 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. The initial flux in the 2.5 s image was 8.20e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 98 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 12:29:16.07 = 187.31697 DEC(J2000) = +47:50:14.4 = 47.83734 with a 90%-confidence error radius of about 0.74 arc sec. This position is 2.3 arc sec. from the center of the XRT error circle. The estimated magnitude is 13.75 with a 1-sigma error of about 0.14. No correction has been made for extinction. Burst Advocate for this burst is R. Gupta (rahulbhu.c157 AT gmail.com) 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/41898. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39963] GRB 250920B: Fermi GBM Final Real-time Localization
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41897 SUBJECT: GRB 250920B: Fermi GBM Final Real-time Localization DATE: 25/09/20 08:56:46 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 08:46:26 UT on 20 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250920B (trigger 780050791.161292 / 250920366). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 190.8, Dec = 47.4 (J2000 degrees, equivalent to J2000 12h 43m, 47d 23'), with a statistical uncertainty of 2.4 degrees. The angle from the Fermi LAT boresight is 56.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920366/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920366/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920366/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41897. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39962] GRB 250920A: BALROG localization (Fermi Trigger 780029651 / GRB 250920121)
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41896 SUBJECT: GRB 250920A: BALROG localization (Fermi Trigger 780029651 / GRB 250920121) DATE: 25/09/20 05:33:44 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 780029651 at 02:54:06 on 20 Sept. 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) = 174.6 deg Decl.(2000.0) = 52.8 deg The 1 sigma statistical error radius is 1.9 deg. We estimate an additional systematic error of 2 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB250920121/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB250920121/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB250920121/json View this GCN Circular online at https://gcn.nasa.gov/circulars/41896. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39961] GRB 250920A: Fermi GBM Final Localization
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41895 SUBJECT: GRB 250920A: Fermi GBM Final Localization DATE: 25/09/20 05:05:52 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> The Fermi GBM team reports the detection of a likely LONG GRB "At 02:54:06.82 UT on 20 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250920 (trigger 780029651/250920121). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 175.27, Dec = 48.96 (J2000 degrees, equivalent to J2000 11h 41m, +48d 57'), with a statistical uncertainty of 1.00 degrees. The angle from the Fermi LAT boresight is 88 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920121/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920121/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920121/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41895. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39960] GRB 250919A/EP250919a: SVOM/VT optical observation
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41894 SUBJECT: GRB 250919A/EP250919a: SVOM/VT optical observation DATE: 25/09/20 02:42:26 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, L. P. Xin, Z. H. Yao, Y. L. Qiu, C. Wu, H. L. Li, 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) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observation of GRB 250919A/EP250919a detected by Fermi/GBM, SVOM/GRM, EP/WXT, NuSTAR, and Glowbug (Fermi GBM team GCN 41874; Wang et al., GCN 41882; Liang et al., GCN 41879; Waratkar & Grefenstette, GCN 41888; Cheung et al., GCN 41891). SVOM/VT began observing the field at 2025-09-19T14:24:05 UTC, 13.92 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Li et al., GCN 41877; Levan et al., GCN 41883; Oates et al., GCN 41886; Lipunov et al., GCN 41893) was clearly detected in both VT_B and VT_R bands. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 14.240 | 47*50 | VT_B | 18.55 | 0.02 14.247 | 46*50 | VT_R | 18.13 | 0.02 Our photometry was 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/41894. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39959] GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41893 SUBJECT: GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time DATE: 25/09/20 00:38:17 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.M.Lipunov (Lomonosov MSU, Moscow), R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA), A.Kuznetsov, A.Sankovich, G.Antipov, P.Balanutsa, E.Gorbovskoy, N.Tiurina, M.Shilova, A.Chasovnikov, V.Topolev, K.Zhirkov, Ya.Kechin, V.Senik, D.Vlasenko(Lomonosov MSU), D.Buckley, (SAAO, South Africa) O.Gress, N.Budnev (ISU, Irkutsk), A.Sosnovskij (Crao RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) MASTER Global robotic Net (Lipunov et al. 2010) started Fermi GRB 250919A (GBM GCN 41874, GCN 41876, GCN 41890; LAT GCN 41884, Ttrigger=00:28:52) observation in alert mode (Lipunov et al. GCN 41875) at MASTER-OAFA and continued as EP GRB 250919 (GCN 41879) since its notice time (Lipunov et al. 41880) Bright optical counterpart MASTER OT J195412.89-485016.4 was detected with peak structure light curve. 24h after GRB detection (GCN 41874) this optical counterpart has unfiltered m_OT~18.3 MASTER observations will be continued This transient was first publishied as EP250919a optical counterpart by Las Cumbres observatory (GCN 41877, t_detection=03:02:52.800 UTC) and as Fermi GRB 250919A/EP250919a optical counterpart by Gemini-South (LEvan et al. GCN 41883) with reshift detection z = 1.145 X-ray counterpart was also detected by Swift (Osborne et al. GCN 41885) with OT afterglow detection by UVOT (Oates et al. GCN 41886), . NuSTAR (GCN 41888) and Svom (41882). View this GCN Circular online at https://gcn.nasa.gov/circulars/41893. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39958] GRB 250916A: Mondy R-band optical observations
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41892 SUBJECT: GRB 250916A: Mondy R-band optical observations DATE: 25/09/19 20:44:29 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) A. Moskvitin (SAO RAS) report on behalf of IKI-GRB-FuN: We observed the field of a long GRB 250916A at the redshift z = 2.015 (de Ugarte Postigo et al., GCN 41863) detected by Fermi/GBM (The Fermi GBM team, GCN 41839), AstroSat/CZTI (Arya et al., GCN 41843), Glowbug (Cheung et al., GCN 41855), Swift/XRT (Osborne et. al, GCN 41862), and NuSTAR (Waratkar et. al, GCN 41871). The observations were carried with the AZT-33IK 1.5m reflector of Sayan Solar Observatory (Mondy) equipped with the CMOS-photometer. The series of 25x120 s images was obtained in the R-band starting on 2025-09-18 at 18:36 UT, i.e. ~2.23 days since GRB. In the stacked image we clearly detect the OT found initially by GOTO (Belkin et al., GCN 41847) and followed-up by (Mohan et al., GCN 41858; Moskvitin et. al, GCN 41859; Burkhonov et al., GCN 41860; Moskvitin et. al, GCN 41870; Zheng & Filippenko, GCN 41873). Preliminary observation results are presented below: Date UT start t-T0 Exp. Filter OT Err. UL (mid, days) (n*s) (3sigma) 2025-09-18 18:36:27 2.23063 25x120 R 20.52 0.02 21.5 The photometry is based on nearby stars of PanSTARRS-DR1 (R-magnitudes were obtained via the Lupton 2005 transformations; see Moskvitin et. al, GCN 41859) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41892. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39957] GRB 250919A: Glowbug gamma-ray detection
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41891 SUBJECT: GRB 250919A: Glowbug gamma-ray detection DATE: 25/09/19 18:58:32 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 250919A, which was also detected by Fermi/GBM (GCN 41874, 41881, 41890), SVOM/GRM (GCN 41882), and NuSTAR (GCN 41888), and associated with the Einstein Probe transient EP250919a (GCN 41879). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-09-19 00:28:56.288 with a duration of 32.1 s and a total significance of about 14.5 sigma. The burst originated toward the Nadir side of Glowbug and was detected despite passing through the passive material from the H9 pallet and internal passive material/shielding within Glowbug. The observed light curve comprises two primary peaks at ~T0+24s and ~T0+28s. Note that data from ~T0+30s to +38s suffered from deadtime in various detectors. 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/41891. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39956] GRB 250919A: Fermi GBM Observation
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41890 SUBJECT: GRB 250919A: Fermi GBM Observation DATE: 25/09/19 18:56:13 GMT FROM: oindabimukherjee(a)gmail.com O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 00:28:52.28 UT on 19 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250919A (trigger 779934537/250919020) which was also detected by Fermi-LAT ( A. Holzmann Airasca et al. 2025, GCN 41884), SVOM-GRM (Chen-Wei Wang et al. 2025, GCN 41882), Swift-XRT (J.P. Osborne et al., 2025, GCN 41885), EP-WXT (Y.F. Liang et al. 2025, GCN 41879), Swift-UVOT (S.R. Oates et al. 2025, GCN 41886), Gemini/GMOS-S spectroscopic redshift z = 1.145 (A. J. Levan et al. 2025, GCN 41883) The Fermi GBM on-ground location is consistent with the position measured by other instruments. The angle from the Fermi LAT boresight is 56 degrees. The GBM light curve consists of a very bright emission episode, followed by a fainter second emission episode, with a total duration (T90) of about 129.3 s (50-300 keV). The time-averaged spectrum from T0+3 to T0+190 s is best fit by a Band function with Epeak = 476 +/- 6 keV, alpha = -0.88 +/- 0.01, and beta = -2.39 +/- 0.04. The event fluence (10-1000 keV) in this time interval is (4.36 +/- 0.002)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+33 s in the 10-1000 keV band is 115.2 +/- 0.7 ph/s/cm^2. The time-averaged spectrum of the main pulse from T0+3 to T0+58 s is best fit by a Band function with Epeak = 475 +/- 5 keV, alpha = -0.7 +/- 0.01, and beta = -2.38 +/- 0.03. The event fluence (10-1000 keV) in this time interval is (2.56 +/- 0.01)E-04 erg/cm^2. The time-averaged spectrum of the second pulse from T0+111 to T0+190 s is best fit by a Band function with Epeak = 220 +/- 12 keV, alpha = -1.12 +/- 0.02, and beta = -1.93 +/- 0.03. The event fluence (10-1000 keV) in this time interval is (5.77 +/- 0.05)E-05 erg/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/41890. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39955] Fermi GRB 250918A: Global MASTER-Net observations report
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41889 SUBJECT: Fermi GRB 250918A: Global MASTER-Net observations report DATE: 25/09/19 18:30:47 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 250918A ( Fermi GBM team, GCN 41865) errorbox 1 days 18846 sec after notice time and 1 days 18882 sec after trigger time at 2025-09-19 17:47:00 UT, with upper limit up to 15.6 mag. Observations started at twilight. The observations began at zenith distance = 60 deg. The sun altitude is -16.5 deg. The galactic latitude b = 38 deg., longitude l = 340 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2994371 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 105313 | 2025-09-19 17:47:00 | MASTER-SAAO | (14h 44m 17.11s , -15d 37m 24.9s) | C | 60 | 15.6 | 105313 | 2025-09-19 17:47:00 | MASTER-SAAO | (14h 46m 06.96s , -15d 52m 16.6s) | C | 60 | 14.9 | 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/41889. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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