TITLE: GCN CIRCULAR NUMBER: 39300 SUBJECT: EP250207b: NOT optical counterpart candidate DATE: 25/02/12 15:11:09 GMT FROM: Dong Xu at NAOC/CAS dxu@nao.cas.cn

X. Liu, J. An, S.Q. Jiang, S.Y. Fu, Z.P. Zhu, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), M. A. Diaz Teodori, R. H. Rasmussen, A. M. Kadela (NOT) report on behalf of a large collaboration:

We observed the field of EP250207b detected by EP/WXT (Zhou et al., GCN39266) using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A total of 4 x 200 s frames in Sloan r-band were obtained at a mid time of 03:16:13 UT on 2025-02-09, i.e., 1.23 days after the EP trigger time.

We performed image subtraction on our stacked image using both PanSTARRS and Legacy Survey images as templates. Within the EP/FXT error circle, an uncatalogued faint source was detected with a magnitude of r ~ 23.7 mag (AB), calibrated against nearby PanSTARRS stars, at coordinates

R.A.(J2000) = 11:10:03.21 Dec.(J2000) = -07:52:07.20

with an uncertainty of ~ 1 arcsec. It is about 10 arcsec away from the galaxy WISEA J111002.65-075211.9 noted by Malesani et al. (GCN 39270) and Levan et al. (GCN 39278). The brightness of the galaxy in our image shows no brightening compared to PanSTARRS kron magnitude.

In addition, the source reported by Fraser et al. (GCN 39287) is not detected in our stacked image, down to a 5-sigma limiting magnitude of r ~ 23.0 mag (AB).

The magnitudes reported above have not been corrected for Galactic extinction.

Further observations are planned and deep r-band photometry of the field is encouraged.

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