TITLE: GCN CIRCULAR NUMBER: 30990 SUBJECT: GRB 211023A: 1.5m OSN optical observation DATE: 21/10/25 13:24:27 GMT FROM: Youdong HU at IAA-CSIC <huyoudong072@hotmail.com> Y.-D. Hu, V. Casanova, T.-R. Sun, A. J. Castro-Tirado, M. D. Caballero-Garcia, M. A. Castro Tirado and E. Fernandez-Garcia (IAA-CSIC), on behalf of a larger collaboration, report: Following the detection of GRB 211023A by Fermi (GCN 30958) and AGILE (Ursi et al. GCNC 30969), images in BVRI bands were obtained at the 1.5m OSN telescope in Sierra Nevada Observatory (Granada, Spain) starting on 24 Oct 22:57 UT. In the first R-band 90 s exposure image, the optical afterglow discovered by MASTER (Zhirkov et al. GCNC 30977) and also reported at OAJ (Kann et al. GCNC 30982) is clearly detected, for which we measure R = 19.27 +/- 0.14 (~1.4 d after trigger). Further observations are ongoing. We thank the staff at OSN for their excellent support.