TITLE: GCN CIRCULAR NUMBER: 37489 SUBJECT: GRB 240911A: JinShan optical upper limits on two Swift/XRT candidates DATE: 24/09/13 16:19:19 GMT FROM: Dong Xu at NAOC/CAS S.Y. Fu, S.Q. Jiang, J. An, Z.P. Zhu, X. Liu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of GRB 240911A detected by SVOM/ECLAIRs (Schanne et al., GCN 37462), using the 50cm-A/B telescopes (50A, 50B) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 16:27:18 UT on 2024-09-12, i.e., 19.8 hr after the trigger, and a series of frames were obtained in the Sloan g-, r-, i- and z-bands. No new optical source is detected within the error circles of two uncatalogued Swift/XRT candidates (Williams et al., GCN 37483), down to the following 5-sigma upper limits: T_mid (UT) | T_mid (hr) | filter | 5-sigma U.L. (AB) ---------------------------------------------------- 2024-09-12T17:18:03.5 | 20.65 | g | 21.1 2024-09-12T16:42:30.0 | 20.06 | r | 21.1 2024-09-12T16:49:22.0 | 20.18 | i | 20.1 2024-09-12T17:24:54.0 | 20.77 | z | 18.8 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.