TITLE: GCN CIRCULAR NUMBER: 41709 SUBJECT: GRB 250904A: TRT optical counterpart detection DATE: 25/09/04 18:36:01 GMT FROM: syfu@nao.cas.cn S.Y. Fu (HUST), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), L.B. He, X. Liu, Z.P. Zhu, S.Q. Jiang, J. An, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of GRB 250904A (Salvaggio et al., GCN 41704), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observations started at 17:49:41.450 UTC on 2025-09-04, i.e., ~ 12.6 min after the Swift/BAT trigger and a series of frames in the R band were obtained. An uncatalogued source is detected in our stacked image within the enhanced Swift/XRT error circle (Evans et al., GCN 41706) with magnitude of R = 20.1 +/- 0.2 (AB) at 18.97 min post-trigger, calibrated with Pan-STARRS1 DR2 catalog converted using Lupton (2005) equations and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41709. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...