TITLE:   GCN CIRCULAR
NUMBER:  34483
SUBJECT: GRB 230818A: SAO RAS Zeiss-1000 observations
DATE:    23/08/19 03:12:38 GMT
FROM:    Moskvitin Alexander at SAO RAS <mosk@sao.ru>

A. S. Moskvitin, D. V. Oparin, V. S. Shergin and
V. V. Komarov (SAO RAS), report on behalf of the GRB follow-up team.

We observed the field of GRB 230818A (Fermi GBM team, 34478;
Tohuvavohu et al., GCN 34479) with the 1-m telescope of SAO RAS
Zeiss-1000 equipped with the CCD photometer. We started observations
on August 18, 23:32:18 UT (~5 minutes after the trigger) and obtained
multiple images in BVRcIc bands (principally in Rc).

We clearly detected the OT (Lipunov et al., GCNs 34476, 34477,
34481, 34482; Gompertz et al., GCN 34480) in our individual
frames with the coordinates
R. A. (J2000) = 19:03:33.11
Decl. (J2000) = +40:53:49.2 (+/- 0".5)
and the following brightness:
UT_start   exp, s    t_mid-T0, h   Rmag +/- err
23:32:18    60       0.0872        17.79 +/- 0.06
23:34:00    60       0.1156        18.07 +/- 0.06
23:45:06   120       0.3089        19.18 +/- 0.08
23:57:27   120       0.5147        19.68 +/- 0.10
00:29:01   300       1.0658        20.52 +/- 0.13
00:45:26   2 x 300   1.39333       20.48 +/- 0.09

This preliminary photometry is based on nearby USNO-B1 stars (R2 mag),
the magnitude is not corrected for MW extinction.