TITLE: GCN CIRCULAR NUMBER: 30178 SUBJECT: GRB 210610B: CrAO/ZTSh optical afterglow photometry DATE: 21/06/10 22:44:37 GMT FROM: Alexei Pozanenko at IKI, Moscow V. Rumyantsev (CrAO), A. Pozanenko (IKI), S. Belkin (IKI), N. Pankov (HSE) report on behalf of GRB IKI FuN: We report photometry of GRB 210610B afterglow (Page et al., GCN 30170; Lipunov et al. GCNs 30173, 30176; Kumar et al. GCN 30174; Rumyantsev et al., GCN 30175; Hu et al., GCN 30177) obtained with ZTSh 2.6m telescope of CrAO observatory. Preliminary photometry of the optical afterglow in R- filter is following Date UT start Filter Exp. OT Err. UL(3sigma) (s) 2021-06-10 20:19:24 R 1*10 16.11 0.02 21.5 2021-06-10 20:59:50 R 1*10 16.99 0.02 21.2 The photometry is based on the nearby USNO-A2.0 star USNO-A2.0_id 1043-0282589 16:15:36.30 +14:23:18.2 R=16.88 We continue observations in BVRI filters and will report photometry after data receiving.