TITLE: GCN CIRCULAR NUMBER: 37298 SUBJECT: GRB 240825A: AstroSat CZTI detection of the long bright burst DATE: 24/08/26 15:39:53 GMT FROM: Gaurav Waratkar at IIT Bombay gauravwaratkar@iitb.ac.in
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 bright long-duration GRB 240825A which was also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 37273), Swift/BAT (R. Gupta et al., GCN Circ. 37274), and INTEGRAL/SPI-ACS (Trigger 10871).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2024-08-25 15:53:01.50 UTC. Due to the extremely bright nature of the GRB, all four quadrants of CZT detectors were saturated. This affects the total counts and peak counts reported. The measured peak count rate associated with the burst is 2791 (+90, -96) counts/s above the background in the combined data of three quadrants (out of four), with a total of 6260 (+168, -178) counts. The local mean background count rate was 251 (+3, -3) counts/s. Using cumulative rates, we measure a T90 of 6.2 (+0.9, -0.8) s. In the preliminary analysis, we find 600 Compton events associated with this event.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2024-08-25 15:53:01.57 UTC. The measured peak count rate associated with the burst is 9409 (+168, -183) counts/s above the background in the combined data of all quadrants, with a total of 24203 (+406, -428) counts. The local mean background count rate was 1473 (+7, -9) counts/s. We measure a T90 of 6.1 (+0.7, -0.6) 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
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