TITLE:   GCN CIRCULAR
NUMBER:  33706
SUBJECT: GRB 230427A: Nanshan/HMT optical upper limit
DATE:    23/04/28 15:38:03 GMT
FROM:    Dong Xu at NAOC/CAS <dxu@nao.cas.cn>

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

We observed the field of GRB 230427A detected by Swift (Troja et al., GCN 33687) using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. Observations started at 14:50:24 UT on 2023-04-27, i.e., 4.3 hr after the Swift/BAT trigger, and 30x60 s unfiltered frames were obtained.

No optical source is detected in our stacked image at the UVOT position (Troja et al., GCN 33687), down to a 3-sigma limiting magnitude m(r) > 21.1 mag (AB) at  4.7 hr post-burst, calibrated with the nearby PanSTAR field in the Sloan r-filter. The magnitude is not corrected for Galactic extinction.