TITLE:   GCN CIRCULAR
NUMBER:  30669
SUBJECT: GRB 210820A: Nanshan/NEXT optical upper limit
DATE:    21/08/21 04:01:10 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>

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

We observed the field of GRB 210820A (Beardmore et al., GCN 30664) using 
the NEXT-0.6m telescope located at Nanshan, Xinjiang, China. We obtained 
10x200 s frames in the Sloan r-band, starting at 21:17:58 UT on 
2021-08-20, i.e., 3.67 hr after the BAT trigger.

No optical source is detected in our stacked image at the Swift/UVOT 
position (Beardmore et al., GCN 30664), down to a limiting magnitude of 
r~21.3, calibrated with the nearby PanSTARRS field.