TITLE: GCN CIRCULAR NUMBER: 32969 SUBJECT: GRB221121A: AstroSat CZTI detection DATE: 22/11/22 10:53:13 GMT FROM: Gaurav Waratkar at IIT,Bombay R. Gopalakrishnan (IUCAA), G. Waratkar (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 GRB221121A which was also detected by Fermi GBM (GCN Circ. 32960). The source was clearly detected in the 20-200 keV energy range. The light curve peaks at 2022-11-21 06:34:50.5 UTC. The measured peak count rate associated with the burst is 173 (+42, -40) counts/s above the background in the combined data of all quadrants, with a total of 1531 (+490, -529) counts. The local mean background count rate was 532 (+3, -4) counts/s. Using cumulative rates, we measure a T90 of 22 (+15, -9) s. It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2022-11-21 06:34:53.9 UTC. The measured peak count rate is 283 (+79, -30) counts/s above the background in the combined Veto data of all quadrants, with a total of 3488 (+696, -662) counts. The local mean background count rate was 1746 (+6, -6) counts/s. We measure a T90 of 22 (+10, -4) s from the cumulative Veto light curve. 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, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.