TITLE: GCN CIRCULAR NUMBER: 31042 SUBJECT: GRB 211023A: optical detection by SBT in Ondrejov DATE: 21/11/05 07:08:47 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz> Jan Strobl, Martin Jelinek, Rene Hudec, Cyril Polasek (ASU CAS Ondrejov, CZ) We observed the optical afterglow of The Fermi/GBM/AGILE GRB 211023A (Fermi GBM team, GCN 30958, Di Lalla et al. GCN 30961, Lesage et al. GCN 30965, Ursi et al. GCN 30969, Poolakkil GCNC 30998) with the double 20cm wide-field Small Binocular Telescope (SBT, cf. Strobl et al., AN 340,7,p.633, 2019) in Ondrejov observatory starting October 25 at 1:19 UT, 36.2h after the GRB detection. The afterglow (Vladimirov et al. GCN 30970, Tiurina 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, Ghosh et al. GCN 31023) is well detected in our 2x80x120s coadded exposure from both tubes: Tmid-T0 Texp mag dmag filter 1.5706d 10762s 19.61 0.13 clear, calibrated as SDSS-r'(AB)