TITLE:   GCN CIRCULAR
NUMBER:  37395
SUBJECT: GRB 240905D: AstroSat CZTI detection
DATE:    24/09/05 17:50:08 GMT
FROM:    Gaurav Waratkar at IIT Bombay <gauravwaratkar@iitb.ac.in>

S. Srijan (IITB), A. Dasgupta (BITS Pilani, Hyderabad), G. Waratkar (IITB), J. Joshi (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 a long-duration GRB 240905D which was also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 37392).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2024-09-05 10:37:40 UTC. The measured peak count rate associated with the burst is 180 (+34, -38) counts/s above the background in the combined data of three (out of four) quadrants, with a total of 845 (+199, -210) counts. The local mean background count rate was 280 (+4, -4) counts/s. Using cumulative rates, we measure a T90 of 16 (+2, -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 19 s for this GRB, with a lower limit of 14 s as estimated above by cumulative rates.

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