GCN Circular 29410

G. Waratkar (IITB), V. Shenoy (IITB), A. Vibhute (IUCAA), S. Gupta 
(IUCAA), P. Sawant (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, 
2020, arxiv:2011.07067) showed detection of a bright long GRB 210204A, 
which was also detected by Fermi-GBM (GCN #29390, #29393) and GECAM-B 
(GCN #29392).

The source was clearly detected in the 20-200 keV energy range. The 
light curve showed two isolated emission peaks with the stronger peak at 
2021-02-04 06:32:45 UT in all four quadrants. The measured peak count 
rate associated with the burst is 789 (+58, -61) cts/s above the 
background in the combined data of four quadrants, with a total of 18141 
(+1631, -1364) cts. The initial fainter peak contributed to about 6% of 
the reported total counts. The local mean background count rate was 480 
(+2, -3) cts/s. Using cumulative rates, we measure a T90 of 200 (+7, 
-10) s.

It was also clearly detected in the CsI anticoincidence (Veto) detector 
in the 100-500 keV energy range. The light curve showed two isolated 
peaks of emission with the stronger peak at 2021-02-04 06:32:45 UT. The 
initial fainter peak contributed less than 5% of total counts and hence 
was excluded from the following analysis. The measured peak count rate 
is 754 (+76, -80) cts/s above the background in the combined Veto data 
of four quadrants, with a total of 15971 (+827, -996) cts. The local 
mean background count rate was 1575 (+2, -3) cts/s. We measure a T90 of 
57 (+7, -5) 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.