P. Sawant (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), S. Gupta (IITB), 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 long GRB 210421B, which was also detected by Fermi-GBM (GCN #29870) and Swift (BAT - GCN #29877).
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 2021-04-21 10:54:43.5 UT. The measured peak count rate associated with the burst is 165 (+42, -33) cts/s above the background in the combined data of four quadrants, with a total of 905 (+230, -297) cts. The local mean background count rate was 504 (+4, -3) cts/s. Using cumulative rates, we measure a T90 of 16 (+3 -10) 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 2021-04-21 10:54:43.647 UT. The measured peak count rate is 320 (+72, -54) cts/s above the background in the combined Veto data of four quadrants, with a total of 1481 (+436, -479) cts. The local mean background count rate was 1629 (+5, -6) cts/s. We measure a T90 of 17 (+4, -11) 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.