GCN 45254: EP 260729a: Ondrejov D50 optical detection supports stellar flare origin

M. Jelinek, J. Strobl, F. Novotny and R. Hudec (ASU CAS Ondrejov) report:

We observed the position of the Einstein Probe transient EP260729a (Zhou et
al., GCN 45253) with the D50 telescope of the Astronomical Institute
Ondrejov, near Prague, Czech Republic, obtaining 19x120s r'-band exposures
starting at 21:13 UT on 2026 July 29 (~4.1 h after the WXT trigger).

We find no uncatalogued object in the error circle down to r>21.5 (3-sigma)
in the combined image.

The M4.0V high proper motion star RX J2350.0+2659 (ATLAS-RefCat2 r=13.876;
Zhou et al., GCN 45253) is bright and well detected in single exposures. It
appears elevated in brightness at the start of our sequence, fading over
~40 minutes. A linear fit gives an initial excess of ~0.14 mag over its
catalogued magnitude, decaying at ~0.1 mag/hour.

This fading excess supports the stellar flare origin of EP260729a suggested
by the EP team (Zhou et al., GCN 45253).