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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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