GCN Circular 29299

D. Nadella (NITK), G. Waratkar (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 210104A, which was
also detected by Fermi-GBM (GCN #29232), Swift-BAT (GCN #29233), Konus-Wind
(GCN #29258) and CALET-CGBM (GCN #29268).

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
2021-01-04 11:27:17.5 UT. The measured peak count rate associated with the
burst is 867 (+60, -56) cts/s above the background in the combined data of
four quadrants, with a total of 7003 (+407, -394) cts. The local mean
background count rate was 555 (+2, -2) cts/s. Using cumulative rates, we
measure a T90 of  33 (+7, -1) 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 2021-01-04 11:27:17 UT. The measured
peak count rate is 606 (+86, -55) cts/s above the background in the
combined Veto data of four quadrants, with a total of 4520 (+693, -789)
cts. The local mean background count rate was 2009 (+4, -5) cts/s. We
measure a T90 of 35 (+7, -14) 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.