GCN Circular 45734
GRB 260924A: GROWTH-India Telescope optical observations
From: Aditya Pawan Saikia at IIT Bombay
Issued: 2026-09-25 00:00 UTC
Type: GRB, Optical Transient

V. Vijaykumar (IITB), A. Sarkar (IITB), S. Patil (IITB), A.P. Saikia (IITB), V. Swain (IITB), T. Mohan (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:

We observed the field of GRB 260924A detected by Fermi (Fermi GBM Team, GCN 45712), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-09-24 22:37:28, i.e., 21.4 hours after the trigger, and obtained multiple exposures in the SDSS r', g' filters. We detect the optical counterpart in our images at the position reported by Evans et al., GCN 45715. The photometric results are as follows:


| MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Magnitude (AB) |
| -------------- | ------ | --------------- | ------------------- | ---------------- |
| 61307.947 | r' | 21.495 | 3x300 | 18.68 +/- 0.04 |
| 61307.959 | g' | 21.774 | 3x300 | 19.63 +/- 0.05 |

The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.

Our results are consistent with other optical observations (Hu et al., GCN 45717 and Izzo et al., GCN 45718)

The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at GROWTH-India (sites.google.com).

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.