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 3x300s 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 3x300s 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.