GCN Circular 40144

M. Tembhurnikar (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 250413A which was also detected by Konus/Wind (reported through GCN Notices).

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 2025-04-13 02:40:16.50 UTC. The measured peak count rate associated with the burst is 225 (+16, -15) counts/s above the background in the combined data of all quadrants, with a total of 4490 (+612, -310) counts. We caution that there is a 0.3 s readout dead time in CZT data during the burst which affects the calculated total counts. The local mean background count rate was 256 (+1, -3) counts/s. Using cumulative rates, we measure a T90 of 75 (+17, -8) s.

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 2025-04-13 02:40:16.24 UTC. The measured peak count rate associated with the burst is 455 (+66, -70) counts/s above the background in the combined data of all quadrants, with a total of 6700 (+786, -821) counts. The local mean background count rate was 1267 (+3, -4) counts/s. We measure a T90 of 74 (+4, -4) 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