TITLE: GCN CIRCULAR NUMBER: 31066 SUBJECT: GRB 211023A: SAO RAS optical observations DATE: 21/11/09 17:32:28 GMT FROM: Moskvitin Alexander at SAO RAS <mosk@sao.ru> A. S. Moskvitin and O. I. Spiridonova (SAO RAS), on behalf of the GRB follow-up team report: We observed the field of GRB 211023A (Fermi GBM team, GCN 30958, Di Lalla et al. GCN 30961, Lesage et al. GCN 30965, Ursi et al. GCN 30969, Poolakkil GCN 30998, Ridnaia et al., GCN 31022) with the SAO RAS 1-m telescope Zeiss-1000 + CCD-photometer on November 9. We obtained 6 x 300 sec. frames in Rc band (00:25:41 -- 01:31:04 UT, T_mid-T0 = 16.4949 days) and 6 x 300 sec. frames in Ic (00:31:28 -- 01:36:45 UT, T_mid-T0 = 16.4989 days). The afterglow (Zhirkov et al. GCN 30977, Kann et al. GCN 30982, Hu et al.GCN 30990, Belkin et al. GCN 31004, Vinko et al. GCN 31008, Belkin et al. GCN 31018, Belkin et al. GCN 31020, Amit Kumar et al. GCN 31023, Rahul Gupta et al. GCN 31041, Strobl et al. GCN 31042, Pozanenko et al. GCN 31053) is clearly detected in our stacked frames with the following brightness: R = 21.69 +/- 0.09, I = 21.27 +/- 0.14 (the preliminary photometry is based on nearby stars of PS1 catalogue, gri -> R and I by Lupton 2005 transformations).