GCN Circular 34725

P. K. Navaneeth (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 230917A which was also detected by KONUS-Wind (reported in IPN_RAW 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 2023-09-17 00:44:43.5 UTC. The measured peak count rate associated with the burst is 217 (+42, -30) counts/s above the background in the combined data of all quadrants, with a total of 2685 (+700, -606) counts. The local mean background count rate was 409 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 67 (+11, -4) 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 2023-09-17 00:44:44.6 UTC. The measured peak count rate associated with the burst is 427 (+67, -68) counts/s above the background in the combined data of all quadrants, with a total of 5334 (+1141, -1259) counts. The local mean background count rate was 1296 (+2, -4) counts/s. We measure a T90 of 89 (+24, -15) 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