TITLE: GCN CIRCULAR NUMBER: 43798 SUBJECT: EP260221a: Xinglong optical upper limit DATE: 26/02/21 20:39:37 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn> Min-He (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 EP260221a (WXT01709258521; Zhang et al., GCN 43791), we observed the field of EP260221a using the 0.8-m and 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x600s g-band frames by using 0.8-m with a median time of 2026-02-21T17:18:37.349, 4 hrs after the EP trigger and 3x600s clear-band frames by using 2.16-m with a median time of 2026-02-21T19:09:10, 6 hrs after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 20 arcsec EP/FXT error circle (Zhang et al., GCN 43791), down to 3-sigma limiting magnitudes of g-band ~15.48 mag for 0.8-m and clear-band 20.71 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/43798. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...