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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 20 Sep '25

20 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 20 Sep '25

20 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 20 Sep '25

20 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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