GCN Circular 35947

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 240317A which was also detected by Fermi GBM (Fermi-GBM team, GCN Circ. 35939
Not found
 
 
).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2024-03-17 09:44:00.50 UTC. The measured peak count rate associated with the burst is 216 (+47, -19) counts/s above the background in the combined data of all quadrants, with a total of 1230 (+201, -216) counts. The local mean background count rate was 383 (+3, -3) counts/s. Using cumulative rates, we measure a T90 of 10 (+2, -4) s. We caution that there is a 0.3 s readout dead time in CZTI data just after the burst. Hence, the T90 can be as large as 13 s for this GRB, with a lower limit of 6 s as estimated above by cumulative rates. 

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2024-03-17 09:43:58.74 UTC. The measured peak count rate associated with the burst is 408 (+77, -67) counts/s above the background in the combined data of all quadrants, with a total of 2969 (+539, -536) counts. The local mean background count rate was 1833 (+8, -9) counts/s. We measure a T90 of 17 (+3, -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