GCN 45527: GRB 260903A: SAO RAS optical upper limit

2026-09-07T11:59:00.672Z | rev 0 | event: GRB 260903A
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 the GRB 260903A discovered by the SVOM
(Brunet et al., GCNs 45499; 45517), and observed by EP (Li et al.,
GCN 45510). Observations were carried out using the SAO RAS
Zeiss-1000 telescope and a new CCD photometer. A set of 18 x 300 sec.
images in Rc band obtained on September 5, 19:34:52--21:25:55 UT
(t_mid - T0 = 2.32851 days).

We do not detect the OT (Li et al., GCN 45504; Saccardi et al.,
GCN 45505; Malesani et al., GCN 45508; Russeil et al., GCN 45509;
Moskvitin et al., GCN 45515; Bochenek and Perley, GCN 45516)
in a stacked image. Details of the observation are the following.

Date,      UTstart, t-T0,   Exp., Filter, Mag,     Err.,     UL
                    (mid,d) (n*s)                          (3-sigma)

2026-09-05 19:34:52 2.32851 18*300 Rc     n/d               24.1

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