GRB 200809B: AstroSat CZTI detection

Analysis of AstroSat CZTI data showed the detection of a long GRB 200809B, which was also detected by Fermi GBM (GCN #28236) and Swift/BAT-GUANO (Tohuvavohu A. et al., GCN #28237). The source was clearly detected in the 40-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2020-08-09 15:41:26.500 UT. The measured peak count rate associated with the burst is 371 +/- 30 cts/s above the background in the combined data of four quadrants, with a total of 706 +/- 7 cts. The local mean background count rate was 537 +/- 1 cts/s. Using cumulative rates, we measure a T90 of 5.44 +/- 0.01 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 2020-08-09 15:41:25.000 UT. The measured peak count rate is 583 +/- 48 cts/s above the background in the combined Veto data of four quadrants, with a total of 785 +/- 19 cts. The local mean background count rate was 1637 +/- 2 cts/s. We measure a T90 of 5.72 +/- 0.45 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.