TITLE: GCN CIRCULAR NUMBER: 30226 SUBJECT: GRB 210610B: optical photometry of afterglow at INASAN/Simeiz DATE: 21/06/12 19:16:14 GMT FROM: Mansur Ibrahimov at INASAN M. Ibrahimov, M. Nalivkin, I. Nikolenko (all from INASAN, Moscow, Russia) and O. Pons (IGA, Havana, Cuba) report on behalf of a larger team: Using Zeiss 1m telescope and 4K FLI PL16803 CCD of Simeiz Obserbatory (Collective Using Center of INASAN), we observed the field of GRB 210610B (Page et al., GCN 30170). 15x120sec images were acquired through Bessel R filter on 2021-06-11/00:03:07 UT (midpoint time, 4.18 hours after the trigger) with a total exposure time of 1800 sec. Optical afterglow (for a list of the most full references see e.g. Hosokawa et al., GCN 30220 and Anandagoda et al., GCN 30221) was clearly seen in all 15 individual R images. Photometry of the optical afterglow using stacked R-image calibrated against USNO-B1 R1-mag of 2 nearby stars, resulted in: R = 17.61 +/- 0.02 mag. Research was supported by Project No. RFMEFI61319X0093 (Russian Ministry of Science and High Education, Agreement No. 075-15-2019-1716 by 2019 Nov 20) and Project No. 19-29-11013 (Russian Foundation of Fundamental Investigation, Agreement No. 19-29-11013\20 by 2021 Jan 21).