TITLE:   GCN CIRCULAR
NUMBER:  38687
SUBJECT: GRB 241228B: TRT optical counterpart confirmation
DATE:    24/12/28 14:25:42 GMT
FROM:    Dong Xu at NAOC/CAS <dxu@nao.cas.cn>

J. An (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Y. Fu, S.Q. Jiang, X. Liu, Z.P. Zhu, S.Y. Gao, D. Xu (NAOC) report on behalf of a large collaboration:

We observed the GOTO optical counterpart candidate (Kumar et al., GCN 38684) of GRB 241228B detected by Fermi (Fermi GBM team, GCN 38682), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia. Observations started at 12:52:57 UTC on 2024-12-28, i.e., 8.7 hr after the Fermi/GBM trigger, and we obtained 4 x 300 s frames in the R filter.

The optical candidate is clearly detected in our stacked image and has decayed to R = 19.20 +/- 0.04 (AB), calibrated with PanSTARRS stars in the field and not corrected for Galactic extinction.