TITLE: GCN CIRCULAR NUMBER: 39808 SUBJECT: GRB 250320B: AstroSat CZTI detection DATE: 25/03/21 09:26:45 GMT FROM: Gaurav Waratkar at IIT Bombay gauravwaratkar@iitb.ac.in
J. Joshi (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 bright long-duration GRB 250320B which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 39792).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-03-20 23:15:29.50 UTC. The measured peak count rate associated with the burst is 350 (+38, -29) counts/s above the background in the combined data of three quadrants (out of four), with a total of 5456 (+403, -388) counts. The local mean background count rate was 207 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 85 (+3, -4) s. In the preliminary analysis, we find 997 Compton events associated with this event.
The source 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 2025-03-20 23:15:28.37 UTC. The measured peak count rate associated with the burst is 2028 (+97, -71) counts/s above the background in the combined data of all quadrants, with a total of 27352 (+899, -1147) counts. The local mean background count rate was 1278 (+4, -4) counts/s. We measure a T90 of 81 (+3, -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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