TITLE:   GCN CIRCULAR
NUMBER:  29438
SUBJECT: GRB 210204A (ZTF21aagwbjr/AT2021buv): continued Mondy optical observations
DATE:    21/02/09 12:40:35 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

S. Belkin (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), N. Pankov (HSE) 
report  on behalf of GRB IKI FuN:

We continued observation of the ZTF21aagwbjr/AT2021buv transient (Kool 
et al., GCN 29405) at the redshift of 0.876 (Xu et al., GCN 29432) which 
is  an afterglow (Kennea et al., GCN 29413; Teja  et al., GCN 29414) of 
  GRB 210204A (Fermi GBM team, GCN 29390; Li et al., GCN 29392; Hurley 
et al., GCN 29408; Waratkar et al., GCN 29410;  Frederiks et al., GCN 
29415). Images in R-filter were taken in AZT-33IK telescope of Sayan
observatory (Mondy) on Feb.7 and Feb.8.

Preliminary photometry of the optical transient in combined images in 
two epochs is following

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

2021-02-07 13:43:58 3.32260  R      60*60 20.61 0.04  22.8  AZT-33IK
2021-02-08 15:22:01 4.39035  R      59*60 20.92 0.05  22.7  AZT-33IK

The photometry does not contradict a possible jet-break suggested by 
Rossi et al (GCN 29433).

The photometry is based on the nearby USNO-B1.0 stars
USNO-B1.0_id R2
1014-0149033 15.43
1014-0149115 17.00