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@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.eyJlbWFpbCI6InZzbmV0LW...