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 bright long-duration GRB 231104A which was also detected by Fermi-GBM (Fermi GBM Team, GCN Circ. 34937), and Swift-BAT (Page et al., GCN Circ. 34938).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2023-11-04 01:47:40.35 UTC. The measured peak count rate associated with the burst is 1905 (+239, -231) counts/s above the background in the combined data of three quadrants (out of four), with a total of 2144 (+214, -227) counts. The local mean background count rate was 232 (+6, -7) counts/s. Using cumulative rates, we measure a T90 of 5 (+1, -1) s. We note that the total count measurements are affected by a 0.3s housekeeping dead time window that coincided with the burst. We also see a faint second peak, consistent with the light curve from Fermi-GBM and Swift-BAT, which is more prominently seen in the Veto detectors as reported below. However, the peak is too weak to make any contribution to the T90 measurements in the CZT lightcurve.
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 2023-11-04 01:47:38.43 UTC. The measured peak count rate associated with the burst is 3448 (+108, -118) counts/s above the background in the combined data of all quadrants, with a total of 14749 (+818, -888) counts. The local mean background count rate was 1357 (+7, -8) counts/s. We measure a T90 of 24 (+1, -18) s from the cumulative Veto light curve. This longer T90 arises from a clear detection of the second peak of the GRB.
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: