TITLE: GCN CIRCULAR NUMBER: 41998 SUBJECT: GRB 250925A: JinShan optical observations DATE: 25/09/26 09:44:45 GMT FROM: liuxing@nao.cas.cn GRB 250925A: JinShan optical observations X. Liu (NAOC), S.Y. Fu (HUST) S.Q. Jiang, J. An, Z.P. Zhu, D. Xu (NAOC), A.D. Zhu, L. Lei (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of GRB 250925A detected by Swift/BAT (Dichiara, GCN 41985), using the 100cm-A (100A) and 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. The 100A observation automatically started at 17:05:21.07 UT on 2025-09-25, i.e., 54.57 seconds after the BAT trigger, and the 100C observation started one hour later. A series of frames were obtained in the Sloan r- and z- bands. The reported optical afterglow (Corcoran et al., GCN41990; Bochenek et al., GCN 41991; Masi et al., GCN 41992; Méndez et al., GCN 41995; Méndez et al., GCN 41995) was detected in our stacked 100C images in both r- and z- bands. Preliminary photometric results are as follows: T-mid (hr) | Filter | Exposure | Mag 2.05 | z | 24x180s | 20.26 +/- 0.15 3.02 | r | 8x200s | 22.10 +/- 0.20 calibrated with nearby Pan-STARRS1 DR2 stars without the Galactic extinction correction. We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41998. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...