TITLE: GCN CIRCULAR NUMBER: 30782 SUBJECT: GRB 210905A: AstroSat CZTI detection DATE: 21/09/07 15:35:29 GMT FROM: Gaurav Waratkar at IIT,Bombay <gauravwaratkar@iitb.ac.in> V. Prasad (IUCAA), P. Sawant (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 CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed detection of a long GRB 210905A, which was also detected by Swift-BAT (Sonbas et al., GCN 30765) and a sub-threshold detection in Fermi-GBM (Veres & Roberts, GCN 30779). 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 2021-09-05 00:12:40.5 UT. The measured peak count rate associated with the burst is 87 (+37.9, -7) cts/s above the background in the combined data of two quadrants (out of four), with a total of 1092 (+250, -294) cts. The local mean background count rate was 286.0 (+2, -2) cts/s. Using cumulative rates, we measure a T90 of 24 (+11, -7) s. CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb [1]. 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. Links: ------ [1] http://astrosat.iucaa.in/czti/?q=grb