TITLE: GCN CIRCULAR NUMBER: 42604 SUBJECT: GRB 251103B: AstroSat CZTI detection DATE: 25/11/06 19:18:43 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com> A. Goyal (IITB), A. Arya (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 GRB 251103B which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 42555), and Swift BAT (Lanava et. al., GCN Circ. 42556). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-11-03 16:46:36.50 UTC. The measured peak count rate associated with the burst is 87 (+31, -16) counts/s above the background in the combined data of three quadrants (out of four), with a total of 307 (+118, -98) counts. We caution that there is a 0.3 s readout dead time in CZT data during the burst which affects the calculated total counts. The local mean background count rate was 215 (+2, -4) counts/s. Using cumulative rates, we measure a T90 of 5.86 (+0.85, -2.24) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-11-03 16:46:41.66 UTC. The measured peak count rate associated with the burst is 148 (+74, -23) counts/s above the background in the combined data of all quadrants, with a total of 677 (+244, -247) counts. The local mean background count rate was 1281 (+6, -7) counts/s. Due to poor statistics, we cannot reliably estimate the T90 from it. 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/42604. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...