GCN Circular 36389

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 long-duration GRB 240503A. Inspection of INTEGRAL/SPI-ACS data also showed the detection of the burst.

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 2024-05-03 13:06:40.5 UTC. The measured peak count rate associated with the burst is 203 (+44, -20) counts/s above the background in the combined data of all quadrants, with a total of 4036 (+511, -541) counts. The local mean background count rate was 436 (+3, -3) counts/s. Using cumulative rates, we measure a T90 of 47 (+3, -3) s.

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 2024-05-03 13:06:40.3 UTC. The measured peak count rate is 306 (+76, -24) counts/s above the background in the combined Veto data of all quadrants, with a total of 5950 (+854, -951) counts. The local mean background count rate was 1359 (+6, -5) counts/s. We measure a T90 of 52 (+5, -5) 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