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@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.eyJlbWFpbCI6InZzbmV0LW...