GCN Circular 29563

S. Belkin (IKI),  A. Pozanenko (IKI),  A. Novichonok (Petrozavodsk State 
University, KIAM),  A. Zhornichenko (KIAM),  N. Pankov (HSE)  report  on 
behalf of IKI GRB FuN:

We observed the field of  GRB 210222B (Gropp et al., GCN 29545) with 
Zeiss-1000 telescope of Koshka observatory starting on Feb. 22 (UT) 
22:46:13, i.e. about 12.8 minutes after GRB trigger. We clearly detect 
optical afterglow  (Gropp et al., GCN 29545; Hu et al., GCN 29546; 
Strausbaugh et al., GCN 29547; Mong et al., GCNs 29548, 29550; Perley et 
al., GCN 29549; Zhu et al., GCN  29551;  Lipunov  et al., GCN 29554; 
Jelinek  et al., GCN 29557; Zheng et al., GCN 29558; Siegel et al., GCN 
29559; Gokuldass et al., GCN 29562). Observations were performed under 
non-optimal weather conditions.

Preliminary photometry of the afterglow is following

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

2020-12-03 20:50:46   0.58216    R      120*25   n/d  n/d   20.5

Date,       UT start  Exptime,s t-T0,d   Filter OT    Err  UL(3sigma)
2021-02-22 22:46:13     240   0,00748842 R      16.27 0.09 18.3
2021-02-22 22:50:18     240   0,01032407 R      16.49 0.11 18.2
2021-02-22 22:55:50     240   0,01416666 R      16.71 0.11 18.2
2021-02-22 22:59:54    5*240  0,02254629 R      17.18 0.18 18.7
2021-02-22 23:20:18    7*240  0,03949074 R      17.60 0.15 18.9


The photometry is based on the nearby USNO-B1.0 stars
USNO-B1.0_id R2
0750-0233028 14.52
0750-0233056 15.22
0750-0233031 15.24

The light curve can be found in
http://grb.rssi.ru/GRB210222B/GRB210222B_LC.png
Based only on our photometry we estimated power law index of the 
afterglow light curve of -0.74.

We are grateful to the ���Terskol Observatory��� Center of the Institute of 
Astronomy of the Russian Academy of Sciences (INASAN) for  the 
observations with the Zeiss-1000 telescope on Mount Koshka at the Simeiz 
Observatory.