TITLE:   GCN CIRCULAR
NUMBER:  29265
SUBJECT: GRB 210104A: Assy continued optical observations
DATE:    21/01/05 22:12:02 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

V. Kim (FAI, Pulkovo Observatory), A. Pozanenko (IKI),  M. Krugov (FAI), 
S. Belkin (IKI), Y. Aimuratov (FAI) report on behalf of GRB IKI FuN:

We continued observations of the GRB 210104A (Fermi GBM team, GCN 29232; 
Troja et al., GCN  29233; Frederiks et al., GCN  29258) with AZT-20 
telescope of Assy-Turgen observatory starting on  Jan. 05 (UT) 12:55:33 
in r'-filter.  We detect the optical afterglow (Troja et al., GCN 
29233; Xin et al., GCN 29235; Hu et al., GCN 29236; Hosokawa et al., GCN 
  29237; Kim et al., GCN 29238; Lipunov et al., GCN 29239; Horiuchi et 
al., GCN 29241; Breeveld et al., GCN 29247; Zhu et al., GCN 29252; Paek 
  et al., GCN 29254; Kumar et al., GCN 29257; Smartt et al., GCN 29262).

Preliminary photometry obtained in images in the beginning of 
observations on Jan. 05 is following

Date       UT start     Filter  Exp.    OT    Err.
                                 (s)

2021-01-04 15:35:27     r'(AB)  20*60   20.85 0.07
2021-01-04 16:20:20     r'(AB)  20*60   21.23 0.10
2021-01-04 17:05:11     r'(AB)  20*60   21.19 0.06

The photometry is based on nearby stars of PanSTARRS-PS1.
Observations are continuing.