TITLE: GCN CIRCULAR NUMBER: 29437 SUBJECT: GRB 210207B: AstroSat CZTI detection DATE: 21/02/09 11:42:14 GMT FROM: Gaurav Waratkar at IIT,Bombay G. Waratkar (IITB), D. Nadella (NITK), V. Shenoy (IITB), A. Vibhute (IUCAA), S. Gupta (IUCAA), P. Sawant (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 bright long GRB 210207B, which was also detected by Swift (BAT - GCN #29420, #29435, XRT - #29422, #29427) Konus-Wind (GCN #29426), AGILE-MCAL (GCN #29428) and Insight-HXMT/HE (GCN #29434). 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 2021-02-07 21:52:49 UT in all four quadrants. The measured peak count rate associated with the burst is 517 (+52, -57) cts/s above the background in the combined data of four quadrants, with a total of 3408 (+384, -451) cts. The local mean background count rate was 560 (+3, -3) cts/s. Using cumulative rates, we measure a T90 of 42 (+10, -2) s. It 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 2021-02-07 21:52:48 UT. The measured peak count rate is 994 (+88, -93) cts/s above the background in the combined Veto data of four quadrants, with a total of 6364 (+849, -894) cts. The local mean background count rate was 1931.8 (+5, -5) cts/s. We measure a T90 of 44 (+9, -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, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.