TITLE: GCN CIRCULAR NUMBER: 40450 SUBJECT: GRB 250507B: AstroSat CZTI detection DATE: 25/05/13 09:42:32 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 250507B which was also detected by SVOM/GRM (SVOM/GRM team, GCN Circ. 40438) and GRBAlpha (Pal et al., GCN Circ. 40441).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-05-07 09:31:33.55 UTC. The measured peak count rate associated with the burst is 158 (+90, -40) counts/s above the background in the combined data of two quadrants (out of four), with a total of 70 (+31, -29) counts. The local mean background count rate was 128 (+5, -8) counts/s. Using cumulative rates, we measure a T90 of 0.7 (+0.2, -0.3) s. We detect only the brighter part of the pulse detected by SVOM/GRM, likely because the source is at a sky position where our effective area is low.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-05-07 09:31:32.65 UTC. The measured peak count rate associated with the burst is 262 (+67, -44) counts/s above the background in the combined data of all quadrants, with a total of 613 (+161, -168) counts. The local mean background count rate was 1220 (+8, -8) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 from it.
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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