GRB 210222B: Zeiss-1000 of Koshka observatory, optical observations

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.