TITLE: GCN CIRCULAR NUMBER: 40319 SUBJECT: GRB 250502A: TRT optical afterglow confirmation DATE: 25/05/02 12:05:04 GMT FROM: Dong Xu at NAOC/CAS dxu@nao.cas.cn

J. An (NAOC), K. Noysena, S. Tinyanont, K. Chanchaiworawit (NARIT), S.Y. Fu (HUST), X. Liu, Z.P. Zhu, S.Q. Jiang, D. Xu (NAOC) report on behalf of a large collaboration:

We observed the field of GRB 250502A detected by SVOM/ECLAIRs (Wang et al., GCN 40313), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observations started at 10:30:05 UTC on 2025-05-02, i.e., ~1.73 hr after the SVOM trigger and a series of frames in the B/V/R/I bands were obtained.

The optical afterglow of the burst (Rakotondrainibe et al., GCN 40315) is clearly detected in our individual images. Preliminary photometry shows that the afterglow has decayed to I ~ 18.6 mag at 2.00 hr post-trigger, calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction.

Observations are ongoing.

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