TITLE:   GCN CIRCULAR
NUMBER:  45707
SUBJECT: GRB 260922A: Ondrejov D50 optical limit
DATE:    26/09/23 15:10:54 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 260922A (Page et al., GCN 45690; Beardmore et al., GCN 45696), detected by Swift (trigger=1512686), with the 50 cm D50 telescope of the Astronomical Institute Ondrejov, Czech Republic. We obtained 3x300 s Sloan r'-band exposures starting at 2026-09-22 18:24 UT, 8.39 h after the trigger.

We do not detect any source at the position of the COLIBRÍ candidate optical counterpart (RA, Dec = 227.90767, +14.21923; Angulo et al., GCN 45699), neither in the individual images (3-sigma limit r' > 19.3) nor in the combined 900 s image (mean epoch T0+8.5 h, 3-sigma limit r' > 20.2). This limit is consistent with the fainter COLIBRÍ detection (r = 22.44) obtained at a later epoch.

Magnitudes are calibrated in Sloan r' (AB) against ATLAS-RefCat2 field stars and are not corrected for Galactic extinction.