TITLE:   GCN CIRCULAR
NUMBER:  46049
SUBJECT: GRB 261026A: Ondrejov D50 optical limit
DATE:    26/10/26 21:27:28 GMT
FROM:    Filip Novotný at Masaryk University <filip.novotny@talentovani.cz>

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

We observed the position of GRB 261026A, detected by SVOM/ECLAIRs and
SVOM/GRM (Goto et al., GCN 46030), with the D50 telescope of the
Astronomical Institute Ondrejov, near Prague, Czech Republic. We obtained
a series of 60s Sloan i'-band exposures between 17:05 and 20:58 UT on
2026 October 26, i.e. 10.9-14.8 h after the trigger. Part of the series
was affected by clouds; 192 frames with good transparency were combined.

We do not detect the optical counterpart at the SVOM/VT position
(RA, Dec = 337.35317, +27.02623; Wu et al., GCN 46035), neither in single
images (3-sigma limit i'>17.3-18.8) nor in the combined 11520 s image
(mean epoch T0+13.13 h, 3-sigma limit i'>20.6).

Photometry is calibrated in Sloan i' (AB system) against ATLAS-RefCat2
field stars, not corrected for Galactic extinction.