TITLE:   GCN CIRCULAR
NUMBER:  46102
SUBJECT: GRB 261029A: Ondrejov D50 optical observations, possible rebrightening
DATE:    26/10/29 23:20:31 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 field of GRB 261029A (Fermi GBM team, GCN 46071;
Goto et al., GCN 46072) with the D50 robotic telescope of the
Astronomical Institute Ondrejov, near Prague, Czech Republic.
We obtained a long series of 60s Sloan i'-band exposures between
starting at 16:42UT on 2026 October 29 (T0+15.3h or 0.64d);
observations are continuing.

The photometry of combined images (15x60s) suggests there has been a
rebrightening or a flat phase, and that the afterglow reached i~19.6 
at 0.75 day post-burst, at which point it starts to be compatible with a
decay again.

Photometry is calibrated in Sloan i' (AB system) against
ATLAS-RefCat2 field stars, not corrected for Galactic extinction
(E(B-V)=0.081 mag).