TITLE: GCN CIRCULAR NUMBER: 31179 SUBJECT: GRB 211206B: AstroSat CZTI detection DATE: 21/12/07 09:58:49 GMT FROM: Gaurav Waratkar at IIT,Bombay V. Prasad (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 ML pipeline (Abraham et al., 2021, MNRAS, 504, 3084) and CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 211206B. 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 2021-12-06 15:10:29.50 UT. The measured peak count rate associated with the burst is 910 (+60, -65) cts/s above the background in the combined data of two quadrants, with a total of 8746 (+348, -398) cts. The local mean background count rate was 467 (+2, -2) cts/s. Using cumulative rates, we measure a T90 of 27 (+1, -1) 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 2021-12-06 15:10:29.09 UT. The measured peak count rate is 823 (+77, -80) cts/s above the background in the combined Veto data of four quadrants, with a total of 7227 (+633, -607) cts. The local mean background count rate was 1432 (+3, -5) cts/s. We measure a T90 of 27 (+4, -2) 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.