TITLE:   GCN CIRCULAR
NUMBER:  29943
SUBJECT: GRB 210424B: AstroSat CZTI detection
DATE:    21/05/05 04:55:36 GMT
FROM:    Varun Bhalerao at Indian Inst of Tech  <varunb@iitb.ac.in>

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 a strong detection of a short GRB 210424B, which was also detected by IPN (GCN #29909) and Konus-Wind (GCN #29911).

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 2021-04-24 08:01:55.150 UT. The measured peak count rate associated with the burst is 2260 (+322, -98) cts/s above the background using 0.1s bins in the combined data of four quadrants, with a total of 1380 (+96, -118) cts. The local mean background count rate was 530 (+9, -11) cts/s. Using cumulative rates, we measure a T90 of 1.24 (+0.13, -0.40)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 2021-04-24 08:01:54.535 UT. The measured peak count rate is 1244 (+89, -98) cts/s above the background in the combined Veto data of four quadrants, with a total of 1822 (+351, -377) cts. The local mean background count rate was 1895 (+5, -6) cts/s. We measure a T90 of 7 (+4, -5) s from the cumulative Veto light curve, though this is most likely an overestimate due to the intrinsic 1s binning of veto data.

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.