TITLE: GCN CIRCULAR NUMBER: 42413 SUBJECT: GRB 251022A: GROWTH-India Telescope optical observations DATE: 25/10/24 01:01:59 GMT FROM: V. Swain at IIT Bombay vishwajeet.s@iitb.ac.in
T. Mohan, V. Swain, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:
We observed the field of Fermi GRB 251022A (Fermi GBM team, GCN 42380), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-10-23 22:25:05 UT, i.e., 23.85 hours after the Fermi trigger. Multiple exposures were obtained in the r'-band, and we clearly detect the optical counterpart in the stacked image. The photometry result follows as:
| MJD (mid) | tmid - t0 (hours) | Filter | Exposure (s) | Magnitude (AB) | | --------- | ----------------- | ------ | ------------ | -------------- | |60971.94474| 24.1 | r' | 5 x 360 | 20.89 +- 0.12 |
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
Our magnitude is consistent with other optical observations (O’Neill et al., GCN 42386; Becerra et al., GCN 42394; Lipunov et al., GCN 42395; Mandarakas et al., GCN 42397).
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 https://sites.google.com/view/growthindia/.
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