TITLE: GCN CIRCULAR NUMBER: 30892 SUBJECT: GRB 210925B: AstroSat CZTI detection DATE: 21/09/28 13:24:23 GMT FROM: Gaurav Waratkar at IIT,Bombay <gauravwaratkar@iitb.ac.in> V. Prasad (IUCAA), P. Sawant (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (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 detection of a long GRB 210925B for which the IPN triangulation (Hurley et al., GCN 30890) was reported. The source was clearly detected in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2021-09-25 01:20:09.75 UT. The measured peak count rate associated with the burst is 887 (+190, -97) cts/s above the background in the combined data of four quadrants, with a total of 1482 (+214, -230) cts. The local mean background count rate was 471 (+5, -9) cts/s. Using cumulative rates, we measure a T90 of 6.3 (+1.9, -2.0) s. It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.