TITLE: GCN CIRCULAR NUMBER: 30889 SUBJECT: GRB 210926A: AstroSat CZTI detection DATE: 21/09/27 13:36:09 GMT FROM: Gaurav Waratkar at IIT,Bombay <gauravwaratkar@iitb.ac.in> P. Sawant (IUCAA), G. Waratkar (IITB), V. Prasad (IUCAA), 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 CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed detection of a long GRB 210926A, which was also detected by GECAM (C. Zheng et al., GCN 30886). 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 2021-09-26 20:52:27.5 UT. The measured peak count rate associated with the burst is 250 (+51, -16) cts/s above the background in the combined data of four quadrants, with a total of 3971 (+446, -463) cts. The local mean background count rate was 480 (+3, -3) cts/s. Using cumulative rates, we measure a T90 of 26 (+6, -5) 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 2021-09-26 20:52:30.9 UT. The measured peak count rate is 262 (+73, -38) cts/s above the background in the combined Veto data of four quadrants, with a total of 3091 (+703, -866 cts. The local mean background count rate was 1512 (+5, -4) cts/s. We measure a T90 of 25 (+14, -10) 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.