TITLE:   GCN CIRCULAR
NUMBER:  26567
SUBJECT: GRB 191221B: AstroSat CZTI detection
DATE:    19/12/23 10:16:07 GMT
FROM:    Ramkrishna Gaikwad at IUCAA/AstroSat  <ramkrishna@iucaa.in>

R. Gaikwad, S. Gupta, V. Sharma, A. Vibhute and D. Bhattacharya (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data showed the detection of a GRB 191221B, which was also detected by Swift (Laha S. et al., GCN #26534), Global MASTER-Net (Lipunov V. et al., GCN #26536), Swift/UVOT (Kuin N. et al., GCN #26538), Swift-XRT (Beardmore A. et al., GCN #26540), AGILE/MCAL (Longo F. et al., GCN #26549), VIRT (Gokuldass P. et al., GCN #26551), VLT/X-shooter (Vielfaure J. et al., GCN #26553), MASTER VWFC (Lipunov V. et al., GCN #26555), LCO (Strausbaugh R. et al., GCN #26560), Zadko (Gendre B. et al., GCN #26561), ALMA (Laskar T. et al., GCN #26564) and iTelescope (Romanov F. et al., GCN #26565).

The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple peaks of emission with the strongest peak at 2019-12-21 20:39:12.0 UT. The measured peak count rate associated with the burst is 708 cts/s above the background in the combined data of four quadrants, with a total of 4829 cts. The local mean background count rate was 515 cts/s. Using cumulative rates, we measure a T90 of 11.16 s.

It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.

CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.