TITLE:   GCN CIRCULAR
NUMBER:  43451
SUBJECT: GRB 260117A: ZTSh optical upper limit
DATE:    26/01/19 11:53:13 GMT
FROM:    Alina Volnova at IKI RAS <alinusss@gmail.com>

A. A. Volnova (IKI), V. Rumyantsev (CrAO), N. Pankov (HSE, IKI), A. S. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:

We observed the field of the SVOM GRB 260117A (Palmerio et al., GCN Circ. 43437) with the ZTSH telescope of CrAO starting on 2026-01-18 at 20:50:34 UT and taking several 120s exposures in R-band. At the position of the source detected by Swift/XRT (Salvaggio et al., GCN 43439; Evans et al., GCN 43438) we do not detect the optical source reported previously by SVOM/VT (Li et al., GCN Circ. 43441) and SVOM/COLIBRÍ (FM-GFT; Fortin et al., GCN 43445). Preliminary photometry is the following:

Date        UT start  t-T0       Exp.    Filter Obj.   Err.   UL       Site/Telescope
                     (mid,days)  (n*s)                       (3sigma)
2026-01-18  20:50:34  1.07354    37*120  R      n/d    n/d    23.2     CrAO/ZTSh

The photometry is based on nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction.