GCN 44929: GRB 260610B / AT2026owq: further SAO RAS optical observations

A. Moskvitin (SAO RAS), O. Spiridonova (SAO RAS), A. Pozanenko (IKI),
A. Volnova (IKI), N. Pankov (IKI) report on behalf of GRB follow-up team

We observed the field of GRB 260610B discovered by Fermi (The Fermi
GBM team, GCN 44891; GCN 44901) with the Zeiss-1000 1-m telescope
of SAO RAS + CCD photometer in BVRcIc filters on June 12.

The OT (O'Neill et al., GCN 44903; Watson et al., GCN 44905;
Zhu et al., GCN 44909; Gillanders et al., GCN 44910; Akl et al.,
GCN 44911; O'Neill et al., GCN 44914; Moskvitin et al., GCN 44918;
Jackson-Horne et al., GCN 44919; Izzo, GCN 44920; Li et al.,
GCN 44921; Bochenek and Perley, GCN 44927) is clearly detected in
our frames with the following brightness:

Date,      UTstart, t-T0,   Exp., Filter, Mag, Err., UL
                    (mid,d) (n*s)                    (3-sigma)
2026-06-12 19:21:03 2.41821 5*300 Rc      20.61 0.03 23.5

This preliminary photometry is based on nearby SDSS stars
(using Lupton 2005 transformation equations) and not corrected
for Galactic extinction.