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
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al.,
2021, JApA, 42, 73) showed detection of a long GRB 210905A, which was
also detected by Swift-BAT (Sonbas et al., GCN 30765) and a
sub-threshold detection in Fermi-GBM (Veres & Roberts, GCN 30779).
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
2021-09-05 00:12:40.5 UT. The measured peak count rate associated with
the burst is 87 (+37.9, -7) cts/s above the background in the combined
data of two quadrants (out of four), with a total of 1092 (+250, -294)
cts. The local mean background count rate was 286.0 (+2, -2) cts/s.
Using cumulative rates, we measure a T90 of 24 (+11, -7) s.
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.