TITLE: GCN CIRCULAR NUMBER: 37565 SUBJECT: EP240919a: JinShan optical upper limits DATE: 24/09/20 09:08:37 GMT FROM: Dong Xu at NAOC/CAS <dxu@nao.cas.cn> S.Q. Jiang, J. An, X. Liu, S.Y. Fu, Z.P. Zhu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of EP240919a detected by EP/WXT (Liang et al., GCN 37561) and likely Fermi/GBM (Liang et al., GCN 37563), using the 100cm-B telescope (100B) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 15:08:25 UT on 2024-09-19, i.e., 14.71 min after the EP/FXT trigger, and a series of frames were obtained in the Sloan r- and i- bands. No new optical source is detected within the EP/FXT error circle (Liang et al., GCN 37561), down to the following 5-sigma upper limits: |T_mid(min)|filter|U.L.(AB)| |47.46 |r| 20.0| |35.79 |i| 19.5| 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/37565. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...