TITLE:   GCN CIRCULAR
NUMBER:  30230
SUBJECT: GRB 210610B: Further SAO RAS optical observations
DATE:    21/06/13 14:58:18 GMT
FROM:    Moskvitin Alexander at SAO RAS  <mosk@sao.ru>

A. S. Moskvitin and O. A. Maslennikova (SAO RAS),
report on behalf of the GRB follow-up team.

We observed the field of the GRB 210610B (Page et al., GCN #30170)
with the SAO RAS 1-m telescope Zeiss-1000 + CCD-photometer in BVRc
Johnson-Cousins filters on June 11 and 12.

The GRB OT is clearly detected in the stacked frames
with the following brightness.

Date     UT_start  UT_end    Exp., s  T_mid-T0, d  R mag
June 11  18:54:36--20:03:45  4 x 300  0.98453      19.33 +/- 0.01
June 11  23:14:36--23:49:13  5 x 300  1.15309      19.62 +/- 0.02
June 12  21:28:37--22:47:50  6 x 300  2.09498      20.67 +/- 0.06

The preliminary photometry is based on the USNO-A2.0 star
from GCN #30178 (Rumyantsev et al.) and previous GCN #30187.
Magnitudes were not corrected for MW extinction.