GCN Circular 42492

Subject

GRB 251013C : 3.4-m telescope of Iranian National Observatory (INO340) optical observations

Event

Date

2025-10-27T20:37:15Z (2 days ago)

From

soroush shakeri at Iranian National Observatory (INO) - Isfahan University of Technology (IUT) <soroush.physic@gmail.com>

Via

Web form

Authors: INO340 Transient Follow-up Team (H. G. Khosroshahi (INO), S. Shakeri (IUT/INO), H. Altafi (INO/IUT), S. Karimi Mianrudi (IUT), Parisa Hashemi (IUT), H. Torkzadeh (IUT), Reza Rezaei (SUT) and Yu Wang (ICRANet).

We report optical follow-up observations of the long-duration GRB 251013C, detected by the Fermi/GBM team (GCN 42221) at 2025-10-13 17:39:41 UT, and subsequently observed by SVOM and Swift/XRT. We observed the field of GRB 251013C with 3.4 m Telescope of Iranian National Observatory (INO340) by using SDSS g, r, and i filters on 2025 October 13, 15, and 16 (UT). We detected the source at the following position

R.A. (J2000.0): 23 03 16 Dec.(J2000.0): -00 12 21

Our first observation was done at 20:36:20 UT on October 13, corresponding to ~10,578 s after the trigger of the Fermi/GBM, and the observation extended to ~2.17 days post-trigger. Photometric calibration was carried out using nearby reference stars from Pan-STARRS and SDSS catalogs. The afterglow shows a consistent fading trend typical of long GRB afterglows and a slight brightening in the second day, with magnitudes decreasing from i = 16.3 ± 0.018 → 21.61 ± 0.34, r = 16.63 ±0.20 → 21.99 ± 0.25, and g = 16.75 ± 0.017→ 22.44 ± 0.16. The deepest stacked images (exp:500s) from the third night reached g = 22.44 ± 0.16 mag.

The optical images

GRB 251013C - Filter-r - 13 Oct

GRB 251013C - Filter-r - 15 Oct

We thank the INO340 technical and scientific staff, M. Bidar, A. Javadi, A. Farhang, H. Shalchian, R. Shomali, R. Ravanmehr, H. Jenab, S. M. Mohajer, H. Sadeghi, M. Rostamian, A. Behnam, A. Karimzadeh, T. Shokatpour, R. Mirzaei, H. Alirezaei, S. Masoudieh.