TITLE: GCN CIRCULAR NUMBER: 41965 SUBJECT: GRB 250920C: TRT optical observation DATE: 25/09/24 13:37:17 GMT FROM: Zipei Zhu at NAOC <zpzhu@nao.cas.cn> Z.P. Zhu (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), L.B. He, X. Liu, J. An, S.Q. Jiang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of GRB 250920C (Fermi GBM team, GCN 41903; Gupta et al., GCN 41904; Mailyan & Meegan, GCN 41917; Gupta et al., GCN 41924; Wang et al., GCN 41929; Panteleeva et al., GCN 41957 ), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observations started at 18:21:14 UTC on 2025-09-20, i.e., ~ 2.9 hours after the Swift/BAT trigger and a series of frames in the R band were obtained. The optical afterglow (Wortley et al., GCN 41907; Strausbaugh et al., GCN 41911; Ghosh et al., GCN 41913; Kuin et al., GCN 41920; Mohan et al., GCN 41925; Sanchez-Ramirez et al., GCN 41928; Guiffreda et al., GCN 41943; de Ugarte Postigo et al., GCN 41951; de Wet et al., GCN 41952; Izzo et al., GCN 41955; Zheng & Filippenko, GCN 41956; ) was clearly detected in our stacked R-band frame with a brightness of 18.87 +/- 0.02, calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41965. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...