GCN 44852: GRB 260604C: 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 long GRB 260604C discovered by Fermi
(The Fermi GBM team, GCN 44822; Neights & Meegan, GCN 44831)
and SVOM (Gotz et al., GCN 44823) with the Zeiss-1000 1-m telescope
of SAO RAS equipped with the CCD photometer. We obtained 12 x 300 sec.
images in Rc band on June 05, 22:25:58--23:33:55 UT.

The OT (Lipunov, GCN 44827; Konno et al., GCN 44828; GCN 44836;
Zhu et al., GCN 44832; Becerra et al., GCN 44834; Hellot et al.,
GCN 44835; Gompertz et al., GCN 44837; Gompertz et al., GCN 44843;
Chen et al.б GCN 44851) is clearly detected in our stacked image
with the following brightness:

Date       UTstart  t-T0    Exp.   Filter Mag +/- Err.    UL
                    (mid,d) (n*s)                         (3-sigma)
2026.06.05T22:25:58 1.11195 12*300 Rc     21.65 +/- 0.07  23.4

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