TITLE: GCN CIRCULAR NUMBER: 39142 SUBJECT: GRB 250204B: AstroSat CZTI detection of a short burst DATE: 25/02/04 16:30:31 GMT FROM: Gaurav Waratkar at IIT Bombay gauravwaratkar@iitb.ac.in

A. Dasgupta (BITS Pilani, Hyderabad), G. Waratkar (IITB), J. Joshi (IUCAA), 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 short-duration GRB 250204B which was also detected by Fermi/GBM (Fermi-GBM Team, GCN Circ. 39141). Inspection of INTEGRAL/SPI-ACS data also showed the detection of the burst.

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-02-04 06:41:14.050 UTC. The measured peak count rate associated with the burst is 446 (+149, -49) counts/s above the background in the combined data of two (out of four) quadrants, with a total of 237 (+60, -71) counts. The local mean background count rate was 116 (+6, -8) counts/s. Using cumulative rates, we measure a T90 of 1.1 (+0.3, -0.5) s.

It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-02-04 06:41:13.502 UTC. The measured peak count rate is 300 (+70, -41) counts/s above the background in the combined Veto data of all quadrants, with a total of 659 (+172, -189) counts. The local mean background count rate was 1265 (+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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