TITLE:   GCN CIRCULAR
NUMBER:  45743
SUBJECT: GRB 260924A: Ondrejov D50 optical afterglow detection
DATE:    26/09/25 12:06:46 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 260924A (D'Elia et al., GCN 45713;
Evans et al., GCN 45715), detected by Swift (trigger=1513082), with the
D50 telescope of the Astronomical Institute Ondrejov, near Prague, Czech
Republic. We obtained 14x120s and 10x60s Sloan r'-band exposures between
03:15 and 03:57 UT on 2026 September 25, i.e. 26.0-26.7 h after the
trigger.

The optical afterglow (Hu et al., GCN 45717; Izzo et al., GCN 45718)
is detected in the combined image (mean epoch T0+26.4 h) at
RA, Dec = 08:55:03.11, +12:02:35.5 (J2000), consistent with the UVOT
position (Klingler et al., GCN 45735), with a magnitude of

r' = 19.12 +/- 0.08 (AB)

Photometry is calibrated in Sloan r' (AB system) against ATLAS-RefCat2
field stars, not corrected for Galactic extinction (E(B-V)=0.041 mag).