TITLE: GCN CIRCULAR NUMBER: 44605 SUBJECT: EP260507a: Xinglong Schmidt optical counterpart detection DATE: 26/05/14 05:07:46 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992@gmail.com> Zhen Wang (SDU), Wenxiong Li, Niu Li, Hu Zou, and Yunao Xiao (NAOC) report: We observed the field of the fast X-ray transient EP260507a (Fu et al., GCN 44488) with the Schmidt telescope at Xinglong Observatory, China. Observations started at May 7 14:09:41 UTC, 0.36 hr after the EP trigger. We obtained a series of 120 s clear-band exposures. The images were processed and stacked with the ASTERIS framework (Guo et al. 2026). PSF photometry was performed using AutoPhOT (Brennan & Fraser 2022). The photometry was calibrated against stars from the DESI Legacy Imaging Surveys catalog in the r band. We detected the optical counterpart reported by Corcoran et al. (GCN 44489), Sankar et al. (GCN 44490), Kumar et al. (GCN 44492), Bochenek et al. (GCN 44494), Eyles-Ferris et al. (GCN 44495), Jiang et al. (GCN 44496), Li et al. (GCN 44497), and Globus et al. (GCN 44498). The measured magnitudes are: T_median (MJD) T-T0 (hr) Exposure (s) Mag (r) 61167.596 0.50 8 x 120 20.37 +/- 0.06 61167.608 0.81 8 x 120 20.55 +/- 0.06 61167.621 1.11 8 x 120 20.94 +/- 0.08 61167.634 1.42 8 x 120 21.08 +/- 0.09 61167.652 1.85 8 x 120 >22.3 (3σ) 61167.685 2.64 12 x 120 21.75 +/- 0.10 The 60/90-cm Schmidt telescope situated at the Xinglong station is supported by the CAS Special Funds for Observatory and Facility Development, alongside a generous contribution from the Zhengjia Enterprise Group. View this GCN Circular online at https://gcn.nasa.gov/circulars/44605. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...