TITLE:   GCN CIRCULAR
NUMBER:  29551
SUBJECT: GRB 210222B: NEXT early optical afterglow observations
DATE:    21/02/23 05:05:58 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>

Z.P. Zhu (NAOC, HUST), S.Y. Fu, X. Liu, D. Xu (NAOC), X. Gao (Urumqi 
No.1 Senior High School), J.Z. Liu (XAO) report:

We observed the field of GRB 210222B (Gropp et al., GCN 29545) using the 
NEXT-0.6m optical telescope located at Nanshan, Xinjiang, China. 
Observations automatically started at 22:39:01 UT on 2021-02-22, i.e., 
95 s after the BAT trigger. We obtained a series of 40 s and 60 s frames 
during the local morning twilight in the Sloan r-filter.

The previously reported optical afterglow (Gropp et al., GCN 29545; Hu 
et al., GCN 29546; Strausbaugh et al., GCN 29547; Mong et al., GCN 
29548, 29550; Perley et al., GCN 29549) is detected in the stacked 
images of the first three exposures, with r = 14.5 +/- 0.3 mag, 
calibrated with nearby PS1 stars.