TITLE:   GCN CIRCULAR
NUMBER:  32853
SUBJECT: GRB 221025A: AstroSat CZTI detection
DATE:    22/10/26 13:42:23 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 CIFT framework (Sharma et al., 
2021, JApA, 42, 73) showed the detection of a short GRB 221025A which 
was also detected by Fermi-GBM (Wood et al,. GCN 32851) and Fermi-LAT 
(Arimoto et al,. GCN 32843).

The source was clearly detected in the 20-200 keV energy range. The 
light curve peaks at 2022-10-25 00:58:18.6 UTC. The measured peak count 
rate associated with the burst is 904 (+212, -102) counts/s above the 
background in the combined data of all quadrants, with a total of 313 
(+62, -63) counts. The local mean background count rate was 435 (+8, 
-12) counts/s. Using cumulative rates, we measure a T90 of 0.45 (+0.6, 
-0.2) s.

It was also detected in the CsI anticoincidence (Veto) detector in the 
100-500 keV energy range. Due to the intrinsic 1 s binning of veto data, 
we cannot reliably estimate a T90 from it.

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.