TITLE: GCN CIRCULAR NUMBER: 39822 SUBJECT: EP250321a: Xinglong 216 decaying optical observations DATE: 25/03/21 19:24:45 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) xinglong@nao.cas.cn

Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Jinlei-Zhang (NAOC), Pengliang-Du (NAOC), Feng-Xiao(NAOC),Zhou-Fan (NAOC), Hong-Wu (NAOC) We performed optical observations of the field of a fast X-Ray transient EP250321a【( Zhu】 et. al, GCN 【39550】; ) in the Free filter using 2.16-m telescope located at Xinglong, Hebei, China. In the band a 600 s exposures were taken , with a median observation time of 2025-03-02T20:32:28, approximately 5 hours after the EP FXT trigger (2025-03-21T17:04:56). We measure a preliminary magnitude of 20.697 +/- 0.267, mag (AB), calibrated against nearby stars from the Pan-STARRS catalog. We summarize our observation results as follows: 1 | 2025-03-02T20:32:28 | 600 s | Free |20.697 +/- 0.267| 2.16-m telescope

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