TITLE: GCN CIRCULAR NUMBER: 39771 SUBJECT: GRB 250317C: AstroSat CZTI detection DATE: 25/03/18 15:13:24 GMT FROM: Gaurav Waratkar at IIT Bombay gauravwaratkar@iitb.ac.in
S. Salunke (IUCAA), 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 long duration GRB 250317C which was also detected by GECAM-C (Wang et al., GCN Circ. 39768).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-03-17 17:31:23.50 UTC. The measured peak count rate associated with the burst is 87 (+34, -21) counts/s above the background in the combined data of three quadrants (out of four), with a total of 356 (+153, -114) counts. The local mean background count rate was 278 (+3, -5) counts/s. Using cumulative rates, we measure a T90 of 8.1 (+1.62, -3.35) 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 2025-03-17 17:31:25.21 UTC. The measured peak count rate associated with the burst is 225 (+62, -64) counts/s above the background in the combined data of all quadrants, with a total of 770 (+299, -346) counts. The local mean background count rate was 1266 (+9, -9) counts/s. We measure a T90 of 8.29 (+1.8, -4.7) 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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