TITLE:   GCN CIRCULAR
NUMBER:  33037
SUBJECT: GRB 221209A: AstroSat CZTI detection
DATE:    22/12/10 02:55:52 GMT
FROM:    Gaurav Waratkar at IIT,Bombay  <gauravwaratkar@iitb.ac.in>

R. Gopalakrishnan (IUCAA), G. Waratkar (IITB), 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 ML pipeline (Abraham et al., 
2021, MNRAS, 504, 3084) and the CIFT framework (Sharma et al., 2021, 
JApA, 42, 73) showed the detection of a bright GRB 221209A which was 
also detected by Fermi-GBM (Fermi GBM team, GCN Circ. 33031) and BALROG 
(Kunzweiler et al., GCN Circ. 33032).

The source was clearly detected in the 20-200 keV energy range. The 
light curve peaks at 2022-12-09 05:50:26.45 UTC. The measured peak count 
rate associated with the burst is 6052 (+437, -209) counts/s above the 
background in the combined data of all quadrants, with a total of 9174 
(+346, -285) counts. The local mean background count rate was 445 (+8, 
-10) counts/s. Using cumulative rates, we measure a T90 of 2.7 (+0.2, 
-0.1) s. In the preliminary analysis, we find 1078 Compton events 
associated with this event.

It was also clearly detected in the CsI anticoincidence (Veto) detector 
in the 100-500 keV energy range. The light curve peaks at 2022-12-09 
05:50:26.18 UTC. The measured peak count rate is 5980 (+136, -150) 
counts/s above the background in the combined Veto data of all 
quadrants, with a total of 12635 (+713, -729) counts. The local mean 
background count rate was 1402 (+8, -7) counts/s. We measure a T90 of 
3.5 (+1.0, -0.6) 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, URSC, IUCAA, SAC, 
and PRL. The Indian Space Research Organisation funded, managed, and 
facilitated the project.