TITLE:   GCN CIRCULAR
NUMBER:  35280
SUBJECT: GRB 231205B: Nanshan/HMT optical upper limit
DATE:    23/12/06 06:40:55 GMT
FROM:    Dong Xu at NAOC/CAS <dxu@nao.cas.cn>

S.Q. Jiang, S.Y. Fu, X. Liu, Z.P. Zhu, J. An, T.H. Lu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:

We observed the field of GRB 231205B detected by Swift (Evans et al., GCN 35269) using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. Observations started at 16:57:41 UT on 2023-12-05, i.e., 13.7 mins after the Swift/BAT trigger, we obtained a series of 20 s, 40 s, 60 s, 90 s, 120 s, 200 s frames without any filter.

No optical source is detected in our stacked image at the Enhanced XRT position (Osborne et al., GCN 35275), down to the 3-sigma limiting magnitude of m(r)>21.3 mag(AB) @ 0.61 hr post-burst, calibrated with the nearby PanSTAR field in the Sloan r-filter and the magnitude is not corrected for Galactic extinction.