TITLE: GCN CIRCULAR NUMBER: 42570 SUBJECT: GRB 251103B: Nanshan/HMT optical upper limit DATE: 25/11/04 06:19:28 GMT FROM: sqjiang at NAOC <sqjiang@bao.ac.cn> S.Q. Jiang (NAOC), S.Y. Fu (HUST), J. An, X. Liu, L.B. He, Z.P. Zhu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report: We observed the field of GRB 251103B detected by Swift/BAT (Lanava et al., GCN 42556) and Fermi/GBM (Fermi GBM team, GCN 42555) using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. Observations started at 22:31:33 UT on 2025-11-03, i.e., 5.749 hrs after the Swift/BAT trigger, we obtained 25x120 s unfiltered frames. No new optical source is detected in our stacked image within the enhanced XRT error circle (Evans et al., GCN 42558), down to the following 3-sigma limiting magnitude R>20.4 at 6.276 hrs post-burst, calibrated with the nearby PanSTARRS field and the magnitude is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42570. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...