GCN Circular 36051

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 long-duration GRB 240408B. 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 2024-04-08 00:10:03.50 UTC. The measured peak count rate associated with the burst is 204 (+36, -23) counts/s above the background in the combined data of three quadrants (out of four), with a total of 3962 (+347, -343) 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 255 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 45 (+13, -6) 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 2024-04-08 00:10:02.74 UTC. The measured peak count rate associated with the burst is 250 (+76, -19) counts/s above the background in the combined data of all quadrants, with a total of 3013 (+491, -495) counts. The local mean background count rate was 1340 (+4, -6) counts/s. We measure a T90 of 26 (+3, -3) 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