TITLE: GCN CIRCULAR NUMBER: 40752 SUBJECT: GRB 250615A / EP250615a: AstroSat CZTI detection DATE: 25/06/17 05:50:31 GMT FROM: Gaurav Waratkar at IIT Bombay gauravwaratkar@iitb.ac.in
M. Tembhurnikar (IUCAA), G. Waratkar (IITB), Harsha K. H. (IUCAA), 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 long duration GRB 250615A / EP250615a which was also detected by Swift/BAT (Dichiara et al., GCN Circ. 40736) and Einstein Probe/WXT (Yang et al., GCN Circ. 40743). The burst location was at an angle of 84 deg from the pointing axis of AstroSat CZTI.
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-06-15 22:25:17.50 UTC. The measured peak count rate associated with the burst is 99 (+31, -11) counts/s above the background in the combined data of two quadrants (out of four), with a total of 983 (+231, -222) counts. The local mean background count rate was 155 (+1, -2) counts/s. Using cumulative rates, we measure a T90 of 22 (+15, -5) 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 2025-06-15 22:25:22.52 UTC. The measured peak count rate associated with the burst is 490 (+70, -50) counts/s above the background in the combined data of all quadrants, with a total of 7176 (+826, -898) counts. The local mean background count rate was 1329 (+7, -8) counts/s. We measure a T90 of 34 (+6, -10) 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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