V. Kim (FAI, Pulkovo Observatory), A. Pozanenko (IKI), N. Pankov (HSE,
IKI), M. Krugov (FAI), S. Belkin (IKI) report on behalf of GRB IKI FuN:
We continue observations of of the field of GRB 210722A (D'Avanzo et
al., GCN 30475; Page et al., GCN 30483; Barthelmy et al. GCN 30489;
Wood et al., GCN30490) with AZT-20 telescope of Assy-Turgen
observatory. We obtained several frames in r' - filter starting on
21-07-24 (UT) 21:34:39. We clearly detect the bright optical afterglow
(D'Avanzo et al., GCN 30475; Zhu et al., GCN 30476; Pankov et al., GCN
30478, 30488, 30494; Kumar et al., GCN 30481; Butler et al., GCN 30484;
Thoene et al., GCN 30487; Jelinek et al., GCN 30492; Fu et al., GCN 30504).
Preliminary photometry of the afterglow in the stacked image is following
Date UT start t-T0 Exp. Filter OT Err. UL(3sigma)
(mid, days) (s) (AB)
2021-07-24 20:56:07 n/d 42*60 r' 21.3 0.2 21.7
The photometry is based on the nearby PS1 stars.
The photometry is still compatible with the single power law of the
afterglow light curve.