TITLE:   GCN CIRCULAR
NUMBER:  29523
SUBJECT: GRB 210217A: NEXT early optical afterglow observations
DATE:    21/02/18 00:20:00 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 210217A (Simpson et al., GCN 29521) using 
the NEXT-0.6m optical telescope located at Nanshan, Xinjiang, China. 
Observations automatically started at 23:27:06 UT on 2021-02-17, i.e., 
84 s after the BAT trigger. A series of 3x40 s, 4x60 s and 10x90 s 
frames in the Sloan r-filter have been obtained, and observations are 
ongoing.

An uncatalogued decaying optical transient is detected at the Swift/UVOT 
position (Simpson et al., GCN 29521), which is thus concluded to be the 
optical afterglow of burst. The afterglow has r = 18.6 +/- 0.2 mag in 
our first image, calibrated with nearby PS1 stars.