TITLE: GCN CIRCULAR NUMBER: 29818 SUBJECT: GRB 210411B: AstroSat CZTI detection DATE: 21/04/15 14:46:58 GMT FROM: Gaurav Waratkar at IIT Bombay P. Sawant (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), S. Gupta (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, 2020, arxiv:2011.07067) showed detection of a long GRB 210411B, which was also detected by Fermi-GBM (GCN #29792). 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 2021-04-11 13:32:55.50 UT. Quadrant D was noisy, and we exclude it from further analysis. The measured peak count rate associated with the burst is 117 (+47, -13) cts/s above the background in the combined data of four quadrants, with a total of 1409 (+320, -296) cts. The local mean background count rate was 492 (+2, -2) cts/s. Using cumulative rates, we measure a T90 of 27 (+4, -5) s. 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.