TITLE: GCN CIRCULAR NUMBER: 40497 SUBJECT: GRB 250520A: AstroSat CZTI detection of a short burst DATE: 25/05/20 09:34:08 GMT FROM: Gaurav Waratkar at IIT Bombay gauravwaratkar@iitb.ac.in
M. Tembhurnikar (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 short duration GRB 250520A which was also detected by Swift/BAT (Eyles-Ferris et al., GCN Circ. 40491), SVOM/GRM (SVOM/GRM team, GCN Circ. 40495), and CALET/GBM (Trigger ID 1431743946).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-05-20 02:42:16.94 UTC. The measured peak count rate associated with the burst is 1106 (+638, -259) counts/s above the background in the combined data of two quadrants (out of four), with a total of 73 (+23, -23) counts. The local mean background count rate was 141 (+22, -43) counts/s. Using cumulative rates, we measure a T90 of 0.15 (+0.03, -0.04) s.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-05-20 02:42:16.12 UTC. The measured peak count rate associated with the burst is 674 (+70, -74) counts/s above the background in the combined data of all quadrants, with a total of 640 (+115, -115) counts. The local mean background count rate was 1161 (+9, -10) 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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