TITLE:   GCN CIRCULAR
NUMBER:  41582
SUBJECT: EP250828a: Seimei/TriCCS optical counterpart detection
DATE:    25/08/29 02:57:38 GMT
FROM:    Kenta Taguchi <kentagch@kusastro.kyoto-u.ac.jp>

Kenta Taguchi (Kyoto U.), Masaomi Tanaka, Seiji Toshikage (Tohoku U.) report on behalf of a larger collaboration:
We observed the field of EP250828a detected by the Einstein Probe (Liu et al., GCN 41574, Aryan et al., GCN 41579) using the Tricolor CMOS Camera and Spectrograph (TriCCS) on the 3.8-m Seimei Telescope at the Okayama Observatory of Kyoto University.
Our observation started at 13:20:39 UT on 2025-08-28 (MJD = 60915.5560).
For each band, we took 37 exposures of 30 seconds (i.e., the total exposure time is 1110 s = 18.5 min).
From our preliminary analysis, the 5 sigma limiting magnitudes are 22.3, 22.1, and 22.5 AB mag for g, r, and i-band, respectively.
Only in the i-band image, we detected an uncatalogued source of 22.3 +/- 0.2 mag at 21:51:34.02 +20:32:36.3 = 327.8917, 20.5434 (J2000), which is within the FXT error circle (16.5 arcsec from the center).