GCN Circular 35575

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 240118D which was also detected by INTEGRAL-SPI-ACS (Trigger Num. 10478).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2024-01-18 07:48:13.55 UTC. The measured peak count rate associated with the burst is 351 (+165, -33) counts/s above the background in the combined data of all quadrants, with a total of 584 (+142, -136) counts. The local mean background count rate was 323 (+7, -10) counts/s. Using cumulative rates, we measure a T90 of 4 (+1, -1) s. We also see a faint second extended peak, consistent with the light curve from INTEGRAL-SPI-ACS, which is more prominently seen in the Veto detectors as reported below.

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 2024-01-18 07:48:12.73 UTC. The measured peak count rate associated with the burst is 1088 (+90, -49) counts/s above the background in the combined data of all quadrants, with a total of 5639 (+649, -701) counts. The local mean background count rate was 1402 (+6, -7) counts/s. We measure a T90 of 30 (+7, -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