TITLE: GCN CIRCULAR NUMBER: 42631 SUBJECT: GRB 251105A: AstroSat CZTI detection DATE: 25/11/10 05:40:22 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com> 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 251105A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 42596), and Swift BAT (J. DeLaunay et al. 2025, GCN 42593). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-11-05 04:41:19.50 UTC. The measured peak count rate associated with the burst is 85 (+32, -10) counts/s above the background in the combined data of three quadrants (out of four), with a total of 1064 (+275, -254) counts. The local mean background count rate was 211 (+3, -3) counts/s. Using cumulative rates, we measure a T90 of 28 (+5, -5) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-11-05 04:41:20.32 UTC. The measured peak count rate associated with the burst is 178 (+72, -15) counts/s above the background in the combined data of all quadrants, with a total of 2223 (+423, -516) counts. The local mean background count rate was 1203 (+6, -5) counts/s. We measure a T90 of 28 (+2, -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/42631. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...