TITLE: GCN CIRCULAR NUMBER: 39122 SUBJECT: GRB 250202B: AstroSat CZTI detection of a bright long GRB DATE: 25/02/02 08:46:15 GMT FROM: Gaurav Waratkar at IIT Bombay gauravwaratkar@iitb.ac.in
S. Srijan (IITB), G. Waratkar (IITB), J. Joshi (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 250202B which was also detected by Fermi/GBM (Fermi-GBM Team, GCN Circ. 39120).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-02-02 03:57:18.0 UTC. The measured peak count rate associated with the burst is 485 (+14, -15) counts/s above the background in the combined data of all quadrants, with a total of 21162 (+462, -483) counts. The local mean background count rate was 262 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 91 (+2, -2) s. In the preliminary analysis, we find 2474 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 2025-02-02 03:57:24.5 UTC. The measured peak count rate is 750 (+7, -8) counts/s above the background in the combined Veto data of all quadrants, with a total of 30918 (+312, -410) counts. The local mean background count rate was 1195 (+1, -1) counts/s. We measure a T90 of 90 (+1, -1) 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
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