TITLE: GCN CIRCULAR NUMBER: 38755 SUBJECT: GRB 250101A: Nanshan/HMT optical observations DATE: 25/01/01 14:55:10 GMT FROM: Dong Xu at NAOC/CAS <dxu@nao.cas.cn> Z.P. Zhu, S.Y. Fu, X. Liu, S.Q. Jiang, J. An, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the optical counterpart of GRB 250101A detected by Swift/BAT (Page et. al., GCN 38752), using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. Observations started at 13:24:51 UT on 2025-01-01, i.e., 121 s after the Swift/BAT trigger, and a series of unfiltered frames with different exposures were obtained. The optical counterpart (e.g., Page et. al., GCN 38752; Li et al., GCN 38753; Mohan et al., GCN 38754) is clearly detected in the individual frames, and the lightcurve shows an initial rise and then a continuous decay. We measured G ~ 18.3 mag at 30 mins post-burst, calibrated with GAIA-DR3 and not corrected for Galactic extinction. Observations are still ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/38755. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...