GCN Circular 33464

G. Waratkar (IITB), M. Dixit (IITB), P K. Navaneeth (IUCAA), A. Vibhute 
(IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/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., 
2021, JApA, 42, 73) showed the detection of a bright long GRB 230309A.

The source was clearly detected in the 20-200 keV energy range. The 
light curve peaks at 2023-03-09 12:32:21.5 UTC. The measured peak count 
rate associated with the burst is 1281.2 (+67.7 -66.2) counts/s above 
the background in the combined data of all quadrants, with a total of 
7527 (+432 -435) counts. The local mean background count rate was 479.4 
(+2.8 -3.5) counts/s. Using cumulative rates, we measure a T90 of 24.96 
(+2.51 -1.55) s.

It was also clearly detected in the CsI anticoincidence (Veto) detector 
in the 100-500 keV energy range. The light curve peaks at 2023-03-09 
12:32:21.5 UTC. The measured peak count rate is 7339.3 (+150.2 -163.3) 
counts/s above the background in the combined Veto data of all 
quadrants, with a total of 36415 (+702 -758) counts. The local mean 
background count rate was 1750.4 (+5.3 -6.0) counts/s. We measure a T90 
of 25.01 (+0.59 -0.59) s from the cumulative Veto light curve.

CZTI is built by a TIFR-led consortium of institutes across India, 
including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research 
Organisation funded, managed, and facilitated the project.

CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb