TITLE: GCN CIRCULAR NUMBER: 39323 SUBJECT: EP250207b: Xinglong optical upper limit DATE: 25/02/14 10:19:21 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) xinglong@nao.cas.cn

Junjie-Jin(NAOC), Haiyang-Mu(NAOC), Yue-Sun(NAOC), Zhou-Fan(NAOC), Hong-Wu(NAOC) report on behalf of a large collaboration: Following the detection of EP250207b by EP-WXT (Zhou et al., GCN 39266 ), we observed the field of EP250207b using Tsinghua-NAOC 0.8-m telescope (TNT) located at Xinglong, Hebei, China. A total of 3600 s N-band exposures were taken , with a median observation time of 2025-02-08T16:39:35, approximately 18.86 hours after the EP FXT trigger (2025-02-07T21:47:56). No optical counterpart was detected, with a 5-sigma limiting magnitude of 19.9, calibrated with Pan-STARRS sources in the field.

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