TITLE: GCN CIRCULAR NUMBER: 23447 SUBJECT: GRB 181121A: AstroSat CZTI detection DATE: 18/11/25 01:24:18 GMT FROM: Vidushi Sharma at IUCAA V. Sharma and D. Bhattacharya (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data showed the detection of a short GRB 181121A, which was also detected by AGILE/MCAL detection (Ursi A. et al., GCN 23429). The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple peaks of emission with strongest peak at 20:43:36.500 UT. The measured peak count rate is 1131.6 cts/s above the background in combined data of four quadrants, with a total of 1279 cts. The local mean background count rate was 477 cts/s. Using cumulative rates, we measure a T90 of 1.4 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.