TITLE:   GCN CIRCULAR
NUMBER:  30212
SUBJECT: GRB 210610A: CrAO/ZTSH optical observations
DATE:    21/06/11 21:17:06 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

N. Pankov (IKI, HSE), A. Pozanenko (IKI), V. Rumyantsev (CrAO),  S. 
Belkin (IKI, HSE)  report on behalf of IKI GRB FuN:

We observed the GRB 210610A (Page  et al., GCN 30170) with ZTSH 2.6m 
telescope of CrAO observatory starting on June 11 (UT) 19:46:53.  The 
optical afterglow  first reported by UVOT (Page  et al., GCN 30170) is 
clearly detected in each of a single image of 120 exposure in R filter.
Preliminary photometry of the afterglow in the first image is following

Date       UT start   t-T0    Filter Exp.    OT      err
                      (mid, days)       (s)

2021-06-11 19:46:53   0.99683 R      1*120   19.50   0.12

The photometry is based on several nearby USNO-B1.0 (R2) stars
USNO-B1.0 id
USNO_B10-1043-00282648
USNO_B10-1043-00282621