TITLE: GCN CIRCULAR NUMBER: 39613 SUBJECT: GRB 250305A: AstroSat CZTI detection DATE: 25/03/07 12:11:29 GMT FROM: Gaurav Waratkar at IIT Bombay gauravwaratkar@iitb.ac.in
M. Tembhurnikar (IUCAA), 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 GRB 250305A which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 39597), and SVOM/GRM (Jin-Peng Zhang et al., GCN Circ. 39602).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-03-05 15:28:58.3 UTC. The measured peak count rate associated with the burst is 517 (+151, -123) counts/s above the background in the combined data of all quadrants, with a total of 135 (+57, -41) 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 271 (+8, -14) counts/s. Using cumulative rates, we measure a T90 of 0.9 (+0.2, -0.7) s.
The source was also weakly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The measured peak count rate associated with the burst is 161 (+53, -55) counts/s above the background in the combined data of all quadrants, with a total of 298 (+140, –157) counts. The local mean background count rate was 897.1 (+5.5, –6.3) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 from it.
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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