TITLE: GCN CIRCULAR NUMBER: 43826 SUBJECT: EP260223a: Xinglong optical upper limit DATE: 26/02/25 06:29:12 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn> Yinan-Zhu (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Yuguang-Sun (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP260223a (GCN Circular 43817), we observed the field of EP260223a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x300s N-band frames by using 2.16-m with a median time of 2026-02-24 10:56:45 (UT), 4 hrs after the EP trigger and 3x300s clear-band frames by using 2.16-m with a median time of 2026-02-21T19:09:10, 8 hrs after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 20 arcsec EP/FXT error circle (GCN Circular 43817), down to 3-sigma limiting magnitudes of N-band ~19.11 mag for 2.16-m, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/43826. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...