TITLE:   GCN CIRCULAR
NUMBER:  33268
SUBJECT: GRB 230204B: AstroSat CZTI detection
DATE:    23/02/05 05:39:45 GMT
FROM:    Gaurav Waratkar at IIT,Bombay  <gauravwaratkar@iitb.ac.in>

G. Waratkar (IITB), P K. Navaneeth (IUCAA), P. Shetty (IITB), A. Ahmad 
(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 the bright long GRB 230204B 
which was also detected by MAXI-GSC (GCN Circ. 33265), SWIFT/BAT-GUANO 
(GCN Circ. 33267), along with CALET, INTEGRAL and FERMI notices.

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 
2023-02-04 21:45:19.5 UTC. The measured peak count rate associated with 
the burst is 175.4 (+27.7 -26.6) counts/s above the background in the 
combined data of all four quadrants, with a total of 7611 (+557 -740) 
counts. The local mean background count rate was 131.2 (+0.7 -0.9) 
counts/s. Using cumulative rates, we measure a T90 of 216.64 (+5.13 
-22.56) s. In the preliminary analysis, we find 3240 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 showed multiple peaks 
of emission with the strongest peak at 2023-02-04 21:45:18.7 UTC. The 
measured peak count rate is 1315.9 (+79.7 -88.8) counts/s above the 
background in the combined Veto data of all four quadrants, with a total 
of 48625 (+1487 -1923) counts. The local mean background count rate was 
1273.2 (+2.4 -1.8) counts/s. We measure a T90 of 212.32 (+2.94 -7.75) 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.