TITLE: GCN CIRCULAR NUMBER: 40822 SUBJECT: GRB 250620A: AstroSat CZTI detection DATE: 25/06/25 11:52:12 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 GRB 250620A which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 40791), Swift/BAT-GUANO (DeLaunay et al., GCN Circ. 40796), and SVOM/GRM (Wang et al., GCN Circ. 40806).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. We see only the initial short duration spike in the CZT detector data. The light curve peaks at 2025-06-20 08:05:18.89 UTC. The measured peak count rate associated with the burst is 853 (+613, -193) counts/s above the background in the combined data of three quadrants (out of four), with a total of 45 (+31, -13) counts. The local mean background count rate was 118 (+14, -102) counts/s. Using cumulative rates, we measure a T90 of 0.11 (+0.03, -0.03) s for the first spike.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. We see both episodes in Veto detectors, separated by about 10 s. The light curve, showing two burst episodes, peaks at 2025-06-20 08:05:27.70 UTC. The measured peak count rate associated with the burst is 368 (+65, -69) counts/s above the background in the combined data of all quadrants, with a total of 821 (+368, -375) counts. The local mean background count rate was 1184 (+7, -8) counts/s. We measure a T90 of 12 (+2, -10) s from the cumulative Veto light curve. The large negative uncertainty arises from the relatively weak detection of the first spike.
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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