GCN Circular 34901
Subject
GRB 231028A: AstroSat CZTI detection
Date
2023-10-29T03:47:02Z (a year 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 long GRB 231028A which was also detected by Fermi-GBM (Fermi GBM Team, GCN Circ. 34893, Veres et al., GCN Circ. 34899), Swift-BAT (Williams et al., GCN Circ. 34894), and Glowbug (Kerr et al., GCN Circ. 34900).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2023-10-28 04:09:14.25 UTC. The measured peak count rate associated with the burst is 66 (+42, -4) counts/s above the background in the combined data of two quadrants (out of four), with a total of 273 (+88, -85) counts. The local mean background count rate was 156 (+1, -4) counts/s. Using cumulative rates, we measure a T90 of 7.8 (+0.9, -3.0) s. We caution that there was a 0.3 s readout dead time in CZTI after the detection of the burst. Hence, the T90 can be as large as 8.7 s for this GRB, with a lower limit of 4.8 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 2023-10-28 04:09:13.77 UTC. The measured peak count rate associated with the burst is 605 (+74, -72) counts/s above the background in the combined data of all quadrants, with a total of 2924 (+529, -560) counts. The local mean background count rate was 1508 (+6, -7) counts/s. We measure a T90 of 6.2 (+2.3, -1.3) 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