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[vsnet-grb-info 40055] GRB 250925A: Enhanced Swift-XRT position
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41988 SUBJECT: GRB 250925A: Enhanced Swift-XRT position DATE: 25/09/25 20:39:16 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L Page, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team: Using 1810 s of XRT Photon Counting mode data and 4 UVOT images, 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 = 341.21375, 46.55573 which is equivalent to: RA (J2000): 22 44 51.30 Dec (J2000): +46 33 20.6 with an uncertainty of 2.3 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team View this GCN Circular online at https://gcn.nasa.gov/circulars/41988. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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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