TITLE: GCN CIRCULAR NUMBER: 40819 SUBJECT: GRB 250620C: AstroSat CZTI detection DATE: 25/06/25 07:20:43 GMT FROM: Gaurav Waratkar at IIT Bombay gauravwaratkar@iitb.ac.in
S.Salunke (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 and bright GRB 250620C which was also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 40794), SVOM/GRM (Chen-Wei Wang et al, GCN Circ. 40807), and Konus-Wind (Svinkin et al, GCN Circ. 40810).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-06-20 16:07:11.50 UTC. The measured peak count rate associated with the burst is 1004 (+55, -46) counts/s above the background in the combined data of two quadrants (out of four), with a total of 8579 (+269, -224) counts. The local mean background count rate was 150 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 31.3 (+0.3, -0.4) s. In the preliminary analysis, we find 1018 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 showed multiple peaks of emission with the strongest peak at 2025-06-20 16:07:10.63 UTC. The measured peak count rate associated with the burst is 4717 (+120, -137) counts/s above the background in the combined data of all quadrants, with a total of 17904 (+519, -667) counts. The local mean background count rate was 1222 (+6, -5) counts/s. We measure a T90 of 31 (+1, -2) 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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