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

[vsnet-grb-info 41077] SVOM/sb25120502: SVOM detection of a faint X-ray transient candidate
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43000 SUBJECT: SVOM/sb25120502: SVOM detection of a faint X-ray transient candidate DATE: 25/12/05 13:40:22 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> W. J. Xie, D. H. Zhao (NAOC), S. Schanne (CEA/Irfu), Marius Brunet, J.-L. Atteia (IRAP) report on behalf of the SVOM mission team: At 2025-12-05T02:57:15 UTC (T0), SVOM/ECLAIRs triggered and located a possible X-ray transient (SVOM burst-id sb25120502). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The transient was only detected by the Image Trigger (IMT), which produced a sequence of 1 alert. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 6.58 in the [8-50] keV energy band over a time window of 20.48 seconds starting at 2025-12-05T02:56:55. After the reception over X-band of the photon by photon data, those have been replayed on ground in the Offline trigger as well as a ground copy of the On-board trigger, by varying the trigger timescales. The event is still detected as a point-like source at the same position in the same energy band as given by the on-board trigger, over the same 20.48 s time-window. The sky images obtained are clean and show no sign of the source before and after that time period. The localization of the best alert is R.A., Dec. 80.9924, -18.2171 degrees: R.A. (J2000) = 5h23m58.16s Dec. (J2000) = -18d13m01.48s with a 90% confidence level (C.L.) radius of 11.88 arcmin (including systematic error of 2 arcmin added in quadrature). No immediate slew was performed on this burst. No X-ray observation could be performed by SVOM/MXT for the time being. No optical observation could be performed by SVOM/VT for the time being. We notice the presence of the High Proper Motion star LP 777-23, located at 9.3 arcmin from the trigger position. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The contact point for this alert is Wenjin XIE: xiewj(a)bao.ac.cn Please contact by the email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/43000. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 41076] GRB 251202A / EP251202a: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 40-cm and 1-m telescopes at McDonald Observatory
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42999 SUBJECT: GRB 251202A / EP251202a: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 40-cm and 1-m telescopes at McDonald Observatory DATE: 25/12/05 12:55:58 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> M. Contreras, J. Basurto Merino, P.G. Berdayes, A. Caballero-Almagro, A. Cerón, F. Díaz-Segado, T. Ferrer-Laviña, B. Gandolfi, V. Ghiraldo, J. Hernández Fung, L. Juliá-Maroto, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, A. Schenone-Zanuzzi, A. Selezneva, T. Tundidor Rodríguez, E. Urquijo-Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL). We report on observations of the optical counterpart of GRB 251202A / EP251202a, detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 42933; and Bala, GCN Circ. 42957), Einstein Probe (EP) (Zhang et al., GCN Circ. 42937; and Liang et al., GCN Circ. 42946), Swift-XRT (Sbarufatti et al., GCN Circ. 42943), AstroSat CZTI (Arya et al., GCN Circ. 42967), Insight-HXMT/HE (Guo et al., GCN Circ. 42970), and SVOM/GRM (Guo et al., GCN Circ. 42997). We observed the field of GRB 251202A / EP251202a with the Las Cumbres Observatory (LCO) 40-cm telescope and one of the two LCO 1-m telescopes located at the LCO node at McDonald Observatory, Texas. The first observation, with the 40-cm telescope, started on 2025-12-02 at 06:29:14 UT, about 4.67 hours after the Fermi and EP trigger. The optical counterpart first reported by Li et al. (GCN Circ. 42934), at a spectroscopic redshift of z = 2.785 (Zhu et al., GCN Circ. 42939), is clearly detected in our images with the following AB magnitudes, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) | telescope --------------------------------------------------------------------------------------- 2025-12-02 06:29:14 18.76 0.18 SDSS r' 300 LCO 40-cm 2025-12-02 07:43:09 19.19 0.08 SDSS g' 180 LCO 1-m 2025-12-02 07:46:39 18.91 0.07 SDSS r' 180 LCO 1-m 2025-12-02 07:50:11 18.71 0.08 SDSS i' 180 LCO 1-m Our results are consistent with other UV and optical observations: Li et al. (GCN Circ. 42934), Lipunov et al. (GCN Circ. 42938), Zhu et al. (GCN Circ. 42939), O’Neill et al. (GCN Circ. 42947), Quirola-Vasquez et al. (GCN Circ. 42948), Kuin and Moss (GCN Circ. 42956), Zheng et al. (GCN Circ. 42964), Ma et al. (GCN Circ. 42966), and Bochenek et al . (GCN Circ. 42977). This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2025B-010). These observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (La Laguna, Tenerife, Canary Islands, Spain). This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5). View this GCN Circular online at https://gcn.nasa.gov/circulars/42999. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 41075] GRB 251203C: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42998 SUBJECT: GRB 251203C: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/12/05 11:31:43 GMT FROM: nikos.mandarakas(a)lam.fr Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Fredd Sanchez Alvarez (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), M. Brunet (IRAP), N. A. Webb (IRAP): We imaged the field of the SVOM GRB 251203C (Brunet et al., GCN 42976) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-12-05T04:55:27 to 2025-12-05T06:22:35 UTC (from 34.36 to 35.81 hours after the trigger) and obtained 3840 seconds of exposure in the r and z filters. The data were reduced, coadded, and analyzed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the Pan-STARRS-DR1 catalog, is in the AB system, and was not corrected for Galactic extinction. In the stacked image, we no longer detect the optical counterpart reported by H.L. Li (GCN Circ. 42987) and D. Turpin et al. (CGN Circ. 42988), down to the following 3σ limit: r > 22.91 z > 22.47 We do detect a nearby extended source with coordinates RA = 51.782, Dec = -7.31, which is also seen in the Pan-STARRS-DR1 catalog, and could potentially correspond to the host of the GRB. The magnitudes we detect are: r = 22.34 +/- 0.14 z = 21.96 +/- 0.14 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/42998. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 41074] GRB 251202A: SVOM/GRM observation
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42997 SUBJECT: GRB 251202A: SVOM/GRM observation DATE: 25/12/05 08:13:34 GMT FROM: guohx(a)ihep.ac.cn SVOM/GRM team: Hao-Xuan Guo, Chao Zheng, Xing-Hao Luo, Chen-Wei Wang, Zheng-Hang Yu, Yue Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Nicolas Dagoneau (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by EP251202a/GRB 251202A at 2025-12-02T01:51:02.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #42933 and #42957), Einstein Probe (Einstein Probe (EP) team, GCN #42934, #42937 and #42946), GOTO (GOTO collaboration, GCN #42947) and Insight-HXMT (Insight-HXMT team, GCN #42970). 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 16 +8/-4 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251202A.png In addition, the position of this burst, as determined by Swift-XRT (RA = 122.11512, Dec = 40.61228, GCN #42943), is located at about 134 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. ECLAIRs was not collecting data at the time of this burst. 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: Hao-Xuan Guo (IHEP)(guohx(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42997. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 41073] GRB 251203A: GECAM-B observation of a burst
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42996 SUBJECT: GRB 251203A: GECAM-B observation of a burst DATE: 25/12/05 07:58:43 GMT FROM: renyz16607(a)163.com Yang-Zhao Ren, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 251203A, at 2025-12-03T08:18:45.150 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #42968), and SVOM/GRM (Ren et al., GCN #42995). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 14 +1/-3 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251203A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/42996. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 41072] GRB 251203A: SVOM/GRM observation
by GCN Circulars 05 Dec '25

05 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42995 SUBJECT: GRB 251203A: SVOM/GRM observation DATE: 25/12/05 05:45:12 GMT FROM: renyz16607(a)163.com SVOM/GRM team: Yang-Zhao Ren, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Nicolas Dagoneau (CEA), Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by GRB 251203A at 2025-12-03T08:18:45.150 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #42968). 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 14.5 +2.5/-1.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251203A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 165.5, Dec = -46.9, GCN #42968), is located at about 94 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-2 to T0+20 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.40 +0.23/-0.28 and the cutoff energy, parameterized as Epeak, is 185 +83/-42 keV. The event fluence (10-1000 keV) in this time interval is (7.87 +0.94/-0.88)E-06 erg/cm^2. The 1s peak spectrum, measured from T0+14.85 to T0+15.85 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -1.65 +0.14/-0.17 and the cutoff energy, parameterized as Epeak, is 1040 +1700/-630 keV. The flux (10-1000 keV) in this time interval is (1.41 +0.13/-0.14)E-06 erg/cm^2/s. The localization of GRB 251203A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251203A_amati.png The localization of GRB 251203A in the 'Yonetoku' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251203A_yonetoku.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: Yang-Zhao Ren (IHEP)(renyz(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42995. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 41071] GRB 251201B: SALT spectroscopic redshift z = 1.599
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42994 SUBJECT: GRB 251201B: SALT spectroscopic redshift z = 1.599 DATE: 25/12/04 23:55:00 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), A. J. Levan (Radboud and Warwick), S. de Wet (DTU Space), A. de Ugarte Postigo (LAM), D. A. H. Buckley (SAAO), A. Martin-Carrillo (UCD), P. M. Vreeswijk (Radboud) report on behalf of a larger collaboration: We observed the optical afterglow of the Swift and Fermi GRB 251201B (Moss et al., GCN 42924; Palafox & Meegan, GCN 42965), using the Robert Stobie Spectrograph (RSS) installed on the 9.2 m Southern African Large Telescope (SALT) at the Sutherland observatory (South Africa). In a 10-s acquisition image, taken with the SALTICAM instrument on 2025 Dec 1.871 UT (4.47 hr after trigger), we measure a magnitude i = 19.25 +- 0.09 AB, calibrated against nearby stars from the Pan-STARRS catalog, and not corrected for Galactic extinction. A 2400-s spectrum was acquired using the PG0700 grating, covering the wavelength range 3600-7500 AA. Faint continuum is detected across the entire spectrum, setting a secure upper limit to the redshift z < 2. Towards the red end, we identify a few weak absorption features, which we match to Mg I 2852, Mg II 2804, 2796, Fe II 2600, 2587, 2383, all at a common redshift of z = 1.599, which we suggest to be the redshift of GRB 251201B. We acknowledge excellent support from the SALT observing staff, in particular Alexei Kniazev and Veronica Van Dyk. View this GCN Circular online at https://gcn.nasa.gov/circulars/42994. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 41070] GRB 251203C: J-band observations with WINTER
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42993 SUBJECT: GRB 251203C: J-band observations with WINTER DATE: 25/12/04 21:59:48 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Benjamin Schneider (LAM), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Viraj Karambelkar (Columbia), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 251203C (Brunet et al., GCN 42976; Wu et al., GCN 42986) 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 2025-12-04T02:48:19 UTC in the J band (~8.2 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 (Turpin et al., GCN 42980; Li et al., GCN 42987; Turpin et al., GCN 42988). We obtain the following 5-sigma upper limit: J ~ 19.3 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/42993. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 41069] GRB 251129B: Glowbug gamma-ray detection of a short burst
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42992 SUBJECT: GRB 251129B: Glowbug gamma-ray detection of a short burst DATE: 25/12/04 21:03:54 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, confirms the detection of the short GRB 251129B, which was detected by AstroSat/CZTI (GCN 42958), Konus-Wind, Swift/BAT, Mars-Odyssey/HEND (GCN 42960), and GECAM-B (GCN 42984). The light curve comprises a single peak at 2025-11-29 09:51:33.20 with a duration of 0.16s. 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 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/42992. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 41068] GRB 251203A: AstroSat CZTI detection
by GCN Circulars 04 Dec '25

04 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42991 SUBJECT: GRB 251203A: AstroSat CZTI detection DATE: 25/12/04 18:21:20 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), A. Arya (IITB), A. Goyal (IITB), U. Pathak (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 251203A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 42968), and Konus-IPN (via IPN 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 2025-12-03 08:19:00.50 UTC. The measured peak count rate associated with the burst is 148 (+38, -16) counts/s above the background in the combined data of three quadrants (out of four), with a total of 775 (+165, -169) counts. The local mean background count rate was 225 (+3, -3) counts/s. Using cumulative rates, we measure a T90 of 15 (+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 multiple peaks of emission with the strongest peak at 2025-12-03 08:18:47.01 UTC. The measured peak count rate associated with the burst is 150 (+70, -22) counts/s above the background in the combined data of all quadrants, with a total of 989 (+427, -457) counts. The local mean background count rate was 1321 (+7, -8) counts/s. We measure a T90 of 15 (+1, -7) 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/42991. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0