TITLE: GCN CIRCULAR NUMBER: 31020 SUBJECT: GRB 211023A: Terskol optical observations DATE: 21/10/28 18:01:05 GMT FROM: Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru> S. Belkin (IKI, HSE), I. Sokolov (INASAN, KIAM), D. Berezin (IC AMER NASU), A. Pozanenko (IKI), N. Pankov (IKI, HSE), G. Butenko (IC AMER NASU) report on behalf of GRB IKI FuN: We observed the GRB 211023A (Fermi GBM team, GCN 30958) with Zeiss-2000 telescope and Zeiss-600 telescope of Terskol observatory. The afterglow of the GRB 211023A (Lipunov et al., GCN 30977; Kann et al. GCN 30982; Hu et al. GCN 30990; Belkin et al., GCN 31004,31018) is clearly detected with Zeiss-2000 and marginally detected with Zeiss-600. Preliminary photometry of the afterglow is following. Date UT start t-T0 Filter Exp. OT Err. UL. Telescope (mid, days) (s) 2021-10-26 15:08:26 3.11542 R 29*180 20.59 0.16 21.8 Zeiss-2000 2021-10-28 01:06:22 4.51191 R 11*180 20.91 0.10 22.5 Zeiss-2000 2021-10-28 00:15:55 4.47895 R 39*60 20.80 0.40 20.7 Zeiss-600 The photometry is based on the nearby USNO-B1.0 stars RA DEC R2 04:53:23.10336 +85:19:26.4720 14.09 04:52:47.26344 +85:22:52.1508 15.75 The updated light curve can be found in http://grb.rssi.ru/GRB211023A/GRB211023A_LC.png