TITLE: GCN CIRCULAR NUMBER: 39515 SUBJECT: EP250226a/GRB 250226A:Xinglong optical follow-up observations DATE: 25/02/27 12:36:12 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) xinglong@nao.cas.cn

Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Sen-Liu (NAOC), JinLei-Zhang (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report: We observed the field of the fast X-ray transient EP250226a/GRB 250226a (Jiang et al., GCN #39482; The Fermi team, GCN #39479) using the the Xinglong 2.16-m telescope located at Xinglong, Hebei, China. We obtained 3600 s R and I-band with the time of 2025-02-26T17:04:55 . The optical object reported by An et al. (GCN #39486) is detected in our image. We measure a preliminary magnitude of R = 21.19 +/- 0.07 and I = 21.68 +/- 0.05 mag (AB), calibrated against nearby stars from the Pan-STARRS catalog. We summarize our observation results as follows: Obs. No. | Time (UTC) | Exposure Time (s) | Filter | Apparent mag (AB) | Telescope Name

1 | 2025-02-26T17:04:55 | 3600 s | R |21.19 +/- 0.07| Xinglong 2.16-cm Telescope

2 | 2025-02-26T18:05:21 | 3600 s | I | 21.68 +/- 0.0 | Xinglong 2.16-m Telescope

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