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GCN Circular 34742

Subject
GRB 230919A: AstroSat CZTI detection
Date
2023-09-20T13:42:29Z (7 months ago)
From
Gaurav Waratkar at IIT Bombay <gauravwaratkar@iitb.ac.in>
Via
Web form
P. K. Navaneeth (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 230919A which was also detected by Fermi-GBM (Fermi GBM Team, GCN Circ. 34737).

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 2023-09-19 16:58:23.95 UTC. The measured peak count rate associated with the burst is 1118 (+205, -166) counts/s above the background in the combined data of all quadrants, with a total of 921 (+115, -92) counts. The local mean background count rate was 406 (+10, -15) counts/s. Using cumulative rates, we measure a T90 of 1.58 (+1.38, -0.23) s. We caution that there are two 0.3 s readout dead time windows in CZTI data immediately after the detection of the burst. Hence, the T90 can be as large as 2.96 s for this GRB, with a lower limit of 1.35 s as estimated above by cumulative rates.

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2023-09-19 16:58:23.55 UTC. The measured peak count rate associated with the burst is 1196 (+82, -86) counts/s above the background in the combined data of all quadrants, with a total of 1796 (+193, -200) counts. The local mean background count rate was 1280 (+6, -6) counts/s. We measure a T90 of 2.1 (+1.2, -0.5) s from the cumulative Veto light curve. Note that this result is limited due to the 1 s native resolution of veto data.

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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