TITLE: GCN CIRCULAR NUMBER: 36961 SUBJECT: GRB 240727A: JinShan optical upper limits DATE: 24/07/28 09:24:29 GMT FROM: Dong Xu at NAOC/CAS <dxu@nao.cas.cn> J. An, S.Y. Fu, S.Q. Jiang, Z.P. Zhu, X. Liu, L.B. He, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of GRB 240727A detected by Swift (Parsotan et al., GCN 36938) using the 100C telescope of the JinShan project located at Altay, Xinjiang, China. A series of Sloan r- and i- band frames were obtained from 15:37:37 UT to 17:13:11 UT on 2024-07-27. No source is detected at the optical afterglow position (Zheng & Filippenko, GCN 36939; Liu et al., GCN 36940; Dubay et al., GCN 36941), down to the 5-sigma upper limits of r ~ 23.0 and i ~ 21.8, calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction. We acknowledge the excellent support from S.W. Luo, M.M. Yang, Z.K. Feng, Q.C. Zhao and L.F. Huo for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/36961. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...