TITLE: GCN CIRCULAR NUMBER: 42503 SUBJECT: GRB 251025B: GROWTH-India Telescope continued multiband optical observations and rebrightening DATE: 25/10/28 12:33:26 GMT FROM: V. Swain at IIT Bombay vishwajeet.s@iitb.ac.in
T. Mohan, V. Swain, S. Patil, 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 SVOM GRB 251025B (Hussein et al., GCN 42437), with 0.7m GROWTH-India Telescope (GIT). Our second epoch started at 2025-10-25 22:07:53 UT, i.e. about 7.73 hours after the SVOM trigger. Multiple exposures were obtained in the r′ and i' filters, and we detect the optical afterglow in our stacked images. The photometry result follows as:
| MJD (mid) | tmid - t0 (hours) | Filter | Exposure (s) | Magnitude (AB) | | --------- | ----------------- | ------ | ------------ | -------------- | |60973.93279| 7.99 | r' | 5 x 360 | 19.97 +- 0.08 | |60973.95429| 8.5 | i' | 5 x 360 | 19.82 +- 0.16 |
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
The optical counterpart has rebrightened by ~0.4 mag over a period of about 5.8 hours since our earlier observation (Mohan et al., GCN 42447), consistent with other reports by Li et al., GCN 42453; Pereyra et al., GCN 42452; Freeberg et al., GCN 42474.
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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