TITLE: GCN CIRCULAR NUMBER: 40475 SUBJECT: GRB 250516A: AstroSat CZTI detection DATE: 25/05/17 04:54:01 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 long duration GRB 250516A which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 40466), and Swift/BAT (Beardmore et al., GCN Circ. 40467).
The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed a single burst of emission that peaked at 2025-05-16 14:35:33.81 UTC. The measured peak count rate associated with the burst is 333 (+66, -72) counts/s above the background in the combined data of all quadrants, with a total of 527 (+187, -195) counts. The local mean background count rate was 1349 (+8, -9) counts/s. We measure a T90 of 2.4 (+1.8, -1.2) s from the cumulative Veto light curve. We note that our T90 is low since we detect just the brightest burst episode from the lightcurve seen in other missions (Fermi/GBM, Swift/BAT). This is likely due to the unfavourable orientation of our detectors with respect to the GRB.
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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