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GCN Circular 35230

Subject
GRB 231129C: AstroSat CZTI detection
Date
2023-11-30T09:47:31Z (3 months ago)
From
Gaurav Waratkar at IIT Bombay <gauravwaratkar@iitb.ac.in>
Via
Web form
G. Waratkar (IITB), P. K. Navaneeth (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 an extremely bright long-duration GRB 231129C which was also detected by Fermi-GBM (Fermi GBM team, GCN Circ. 35217), MAXI/GSC (Kawakubo et al., GCN Circ. 35223), and CALET (Shimizu et al., GCN Circ. 35228).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. Based on the orientation of the CZTI, the burst saturated two quadrants (A, B out of four). We report two versions of our analysis of CZT data: one from two unsaturated quadrants (C, D), and the other for all four quadrants by including unsaturated data segments from A, B. 

For the two unsaturated quadrants C and D, the light curve peaks at 2023-11-29 19:10:18 UTC. The measured peak count rate associated with the burst is 1189 (+237, -8) counts/s above the background in the combined CD data, with a total of 3838 (+150, -144) counts. The local mean background count rate was 155.1 (+3.7, -5.9) counts/s. Using cumulative rates, we measure a T90 of 5.1 (+0.2, -0.2) s in these two quadrants. 

Using unsaturated data segments from all four quadrants, we report that burst duration was 6.7 (+0.2, -0.2) s. We also report a minimum peak count rate of 4164.2 (+328.9, -329.3) counts/s at a local mean background count rate of 334.8 (+6.7, -7.4) count/s, with a total of at least 8061 (+195, -236) counts. In the preliminary analysis, we find 1362 Compton events associated with this event in all four quadrants.

It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2023-11-29 19:10:18.69 UTC. The measured peak count rate is 4408 (+125, -126) counts/s above the background in the combined Veto data of all quadrants, with a total of 18860 (+406, - 410) counts. The local mean background count rate was 1511.3 (+6.5, -7.7) counts/s. We measure a T90 of 5.5 (+0.2, -0.2) 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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