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.