GCN Circular 45720
GRB 260924A: AstroSat CZTI detection
From: ABHINAV GOYAL at Indian Institute of Technology, Bombay
Issued: 2026-09-24 11:11 UTC
Type: GRB, Gamma-ray Transient, X-ray Transient

S. Salunke(IUCAA), Harsha K. H. (IUCAA), A. Goyal (IITB), A. Arya (IITB), S. Puri (IITB), G. Waratkar (CalTech/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 GRB 260924A which was also detected by Fermi (Fermi GBM team, GCN Circ. 45712), Swift BAT (D'Elia et. al, GCN Circ. 45713).

The source was detected in the CZT detectors in the 20-200 keV energy range. The light curve showed two distinct peaks of emission separated by ~ 170 s with the strongest peak at 2026-09-24 01:14:33.76 UTC. The measured peak count rate associated with the burst is 249 (+20, -7) counts/s above the background in the combined data of all quadrants, with a total of 20185 (+885, -1029) counts. The local mean background count rate was 250 (+1, -1) counts/s. We measure a T90 of 336 (+1, -7) s from the cumulative CZT light curve.

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed two distinct peaks of emission separated by ~ 170 s with the strongest peak at 2026-09-24 01:15:16.62 UTC. The measured peak count rate associated with the burst is 1019 (+33, -35) counts/s above the background in the combined data of all quadrants, with a total of 71944 (+1628, -1717) counts. The local mean background count rate was 642 (+2, -2) counts/s. We measure a T90 of 336 (+1, -1) s from the cumulative Veto light curve.

CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/ET20260924T011328/ET20260924T011328_details.html

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

Filter: gamma-ray bursts are posted only if in the top 10% of the past year's — by fluence (total energy received per cm², from Fermi GBM, Konus-Wind, GECAM and similar circulars; now ≥ 3.9×10^-5 erg/cm²) or by the number of GCN Circulars about the burst (now ≥ 14). Thresholds are recalculated monthly.
Relayed automatically from NASA's General Coordinates Network.