TITLE:   GCN CIRCULAR
NUMBER:  23867
SUBJECT: GRB 190204A: Mondy optical upper limit
DATE:    19/02/04 18:55:55 GMT
FROM:    Alina Volnova at SAI MSU  <alinusss@gmail.com>

A. Volnova (IKI),  A. Pozanenko (IKI),  E. Klunko (ISTP), R. Inasaridze
(AbAO), E. Mazaeva (IKI), S. Belkin (IKI)  report   on behalf of
IKI-GRB-FuN:

We observed the field of localization of  GRB 190204A   (Lien et al. GCN
23852)    with AZT-33IK telescope of Sayan observatory (Mondy).   We
started observations on Feb. 04 (UT) 13:10:12 in R-filter. We do not
detect  the optical afterglow (Lien et al.  GCN 23852; Watson et al.,
GCN  23861;  Kuin et al., GCN  23863). Preliminary photometry of the
field is following.

Date               UT start      t-T0          Filter Exp.   OT     Err.
  UL
                                         (mid, days)        (s)
                (3 sigma)

2019-02-04  13:10:12  0.32583     R      25*120      n/d     n/d   20.3

The photometry is based on nearby SDSS stars:
SDSS_id                         R_Lupton
J232549.70+545348.8 16.978 0.014
J232550.46+545253.5 17.052 0.014
J232544.33+545253.6 16.085 0.013


Our observation confirm rapid initial decay of the afterglow detected by
UVOT (Kuin et al., GCN  23863).