TITLE: GCN CIRCULAR NUMBER: 39864 SUBJECT: FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060 DATE: 25/03/24 17:09:34 GMT FROM: sqjiang at NAOC <sqjiang@bao.ac.cn> S.Q. Jiang, Z.P. Zhu, X. Liu, J. An (NAOC), S.Y. Fu (HUST), D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), A. M. Kadela, A. A. Djupvik (NOT) report on behalf of a large collaboration: We observed the field of the X-ray candidate EP J120944.2+585060 (Sun et al., GCN 39834; ATel #17100) possibly associated with FRB 250316A (Ng et al., ATel #17081; Leung et al., ATel #17086), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. The mid time of the observations is 01:00:20.3 UTC on 2025-03-23, and a series of 300 s frames were obtained in the Sloan r-band. No new optical source is detected in the stacked image within the EP/FXT error region by subtracting the stacked image against the Legacy Survey template. The 5-sigma limiting magnitude of the observations is r > 24.0, calibrated with Legacy Survey DR 10 and not corrected for Galactic extinction. The non-detection of an optical counterpart is consistent with previous reports by Becerra et al. (ATel #17082; GCN 39843; GCN 39853), Niino et al. (ATel #17084), Hashimoto et al. (ATel #17095), Yang et al. (ATel #17101), Aryan et al. (GCN 39839) and Pereyra et al. (GCN 39858). View this GCN Circular online at https://gcn.nasa.gov/circulars/39864. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...