GRB 240828A: AstroSat CZTI detection of a long burst

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long-duration GRB 240828A which was also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 37317) and INTEGRAL/SPI-ACS (Trigger 10876). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2024-08-28 14:55:46 UTC. The measured peak count rate associated with the burst is 368 (+43, -46) counts/s above the background in the combined data of all quadrants, with a total of 4077 (+335, -387) 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 329 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 39.6 (+1.5, -1.0) s. It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2024-08-28 14:55:45 UTC. The measured peak count rate is 1695 (+94, -66) counts/s above the background in the combined Veto data of all quadrants, with a total of 24765 (+699, -823) counts. The local mean background count rate was 1491 (+5, -6) counts/s. We measure a T90 of 39.6 (+0.5, -0.3) 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