TITLE: GCN CIRCULAR NUMBER: 37500 SUBJECT: EP240913a: JinShan optical upper limits DATE: 24/09/14 11:31:29 GMT FROM: Dong Xu at NAOC/CAS <dxu@nao.cas.cn> Z.P. Zhu, S.Y. Fu, S.Q. Jiang, J. An, X. Liu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of EP240913a detected by Einstein Probe (EP, Li et al., GCN 37492), using the 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 16:48:02 UT on 2024-09-13, i.e., 5.1 hr after the EP trigger, and a series of frames were obtained in the Sloan r- and z-bands. No new optical source is detected within the error circle of the proposed X-ray counterpart (Jiang et al., GCN 37497), down to the following 5-sigma upper limits: T_mid (UT) | T_mid (hr) | filter | Exposue|5-sigma U.L. (AB) 2024-09-13T17:59:25 | 6.331 | r | 13x200s +10x300s | 21.9 2024-09-13T17:29:08 | 5.827 | z | 9x200s | 19.3 calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction. We acknowledge the excellent support from X. Yao, S.W. Luo, and Z.K. Feng for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/37500. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...