TITLE: GCN CIRCULAR NUMBER: 40074 SUBJECT: EP250404a: Seimei/TriCCS optical counterpart detection DATE: 25/04/05 09:09:53 GMT FROM: Kenta Taguchi <kentagch@kusastro.kyoto-u.ac.jp> Kenta Taguchi, Keiichi Maeda (Kyoto U.), Masaomi Tanaka (Tohoku U.) report on behalf of a larger collaboration: We observed the field of EP250404a detected by Einstein Probe (Hu et al., GCN 40051) using the Tricolor CMOS Camera and Spectrograph (TriCCS) on the 3.8-m Seimei telescope. Observations started at 15:27:48 UT on 2025-04-04 (MJD = 60769.64). We detected a counterpart at a position consistent with the source detected by Jiang et al. (GCN 40052, also reported by Perez-Garcia et al. GCN 40053, Du et al. GCN 40058, Konno et al. GCN 40063, Odeh et al. GCN 40064, He et al. GCN 40069, Pérez-Fournon et al. GCN 40071, Jelinek et al. GCN 40072, Rakotondrainibe et al. GCN 40073). Preliminary analysis gives the following magnitudes of the source: g = 18.20 +- 0.05 r = 17.46 +- 0.04 i = 17.10 +- 0.03 View this GCN Circular online at https://gcn.nasa.gov/circulars/40074. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...