GCN Circular 42319
Subject
GRB 251013C: JinShan observations of the non-thermal rebrightening of the optical counterpart
Event
Date
2025-10-17T05:58:17Z (a day ago)
From
L. B. He at NAOC <helb@bao.ac.cn>
Via
Web form
L.B. He, X. Liu, J. An, S.Q. Jiang, Z.P. Zhu, D. Xu (NAOC), S.Y. Fu, A.D. Zhu, L. Lei, H.Z. Wu (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of GRB 251013C (Fermi GBM team, GCN 42221; Rakotondrainibe et al., GCN 42222) using the 100C telescope of the JinShan project, located at Altay, Xinjiang, China. Observations started at 2025-10-16 13:23:15 UT, i. e., 2.822 days after the trigger, and a series of 300s frames in g, r, i, and z bands were obtained.
The previously reported optical counterpart (e.g., Palmerio et al., GCN 42223; and many late GCNs) was clearly detected in all the four bands.
Our preliminary analysis gives r = 21.04 +/- 0.06 at a median time 69 hrs post-burst. The magnitude was calibrated with nearby Pan-STARRS1 dr2 catalog and without the Galactic extinction correction, being consistent with the rebrightening reported in Méndez et al. (GCN 42318).
The SED from the g/r/i/z bands is non-thermal, being consistent with the behavior of GRB optical afterglows. Also a SN1998bw-like supernova would be much fainter at this redshift (z=0.572).
We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations.