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GCN Circular 35166

Subject
GRB 231122B: AstroSat CZTI detection
Date
2023-11-23T06:38:32Z (3 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 a bright long-duration GRB 231122B which was also detected by GECAM-B (Wang et al., GCN Circ. 35157), Glowbug (Cheung et al., GCN Circ. 35161), Swift-BAT GUANO (Ronchini et al., GCN Circ. 35164), and CALET (Asaoka et al., GCN Circ. 35165).

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 2023-11-22 15:13:12.50 UTC. The measured peak count rate associated with the burst is 456 (+42, -40) counts/s above the background in the combined data of three quadrants (out of four), with a total of 7475 (+364, -396) counts. The local mean background count rate was 240 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 34.1 (+1.7, -1.2) s. We caution that there is a 0.3 s readout dead time in CZTI data just before the burst. Hence, the T90 can be as large as 35.8 s for this GRB, with a lower limit of 32.9 s as estimated above by cumulative rates. In the preliminary analysis, we find 685 Compton events associated with this event.

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2023-11-22 15:13:11.68 UTC. The measured peak count rate associated with the burst is 538 (+68, -48) counts/s above the background in the combined data of all quadrants, with a total of 7112 (+819, -804) counts. The local mean background count rate was 1220 (+5, -6) counts/s. We measure a T90 of 32 (+2, -1) s from the cumulative Veto light curve.

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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