TITLE:   GCN CIRCULAR
NUMBER:  32902
SUBJECT: GRB 221027C: AstroSat CZTI detection
DATE:    22/11/01 11:39:51 GMT
FROM:    Gaurav Waratkar at IIT,Bombay  <gauravwaratkar@iitb.ac.in>

M. Dixit (IITB), R. Gopalakrishnan (IUCAA), G. Waratkar (IITB), V. 
Prasad (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 long GRB 221027C.

It was clearly detected in the CsI anticoincidence (Veto) detector in 
the 100-500 keV energy range. The light curve peaks at 2022-10-27 
11:01:02.643 UTC. The measured peak count rate is 430.9 (+76.5, -42.7) 
counts/s above the background in the combined Veto data of all 
quadrants, with a total of 1296 (+366, -418) counts. The local mean 
background count rate was 1406.0 (+6.2, -6.7) counts/s. We measure a T90 
of 5.3 (+5.9, -3.0) s from the cumulative Veto light curve.

The source was also faintly detected in the 20-200 keV energy range. The 
light curve peaks at 2022-10-27 11:01:04.500 UTC. The measured peak 
count rate associated with the burst is 96.1 (+45.0, -6.1) counts/s 
above the background in the combined data of three quadrants, with a 
total of 368 (+128, -149) counts. The local mean background count rate 
was 349.1 (+2.7, -2.7) counts/s. Using cumulative rates, we measure a 
T90 of 6.4 (+0.6, -3.9) 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, URSC, IUCAA, SAC, 
and PRL. The Indian Space Research Organisation funded, managed, and 
facilitated the project.