GCN Circular 30655

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,
2020, arxiv:2011.07067) showed detection of a bright long GRB 210818A,
which was also detected by Swift-BAT (Beardmore et al., GCN #30652),
Swift-XRT (Osborne et al., GCN #30653) and AGILE (Ursi et al., GCN
#30654). 

The source was clearly detected in the 20-200 keV energy range, with the
strongest peak at 2021-08-18 01:02:10.5 UT in the single-peak light
curve. The measured peak count rate associated with the burst is 1018
(+64, -64) cts/s above the background in the combined data of four
quadrants, with a total of 13993 (+552, -512) cts. The local mean
background count rate was 526 (+3, -3) cts/s. Using cumulative rates, we
measure a T90 of 33 (+4, -3) s. 

It was also clearly detected in the CsI anticoincidence (Veto) detector
in the 100-500 keV energy range, with the strongest peak at 2021-08-18
01:02:09.9 UT in the single-peak light curve. The measured peak count
rate is 3748 (+116, -126) cts/s above the background in the combined
Veto data of four quadrants, with a total of 52829 (+844, -1097) cts.
The local mean background count rate was 1616 (+5, -5) cts/s. We measure
a T90 of 37 (+3, -2) 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 [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:
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[1] http://astrosat.iucaa.in/czti/?q=grb