TITLE:   GCN CIRCULAR
NUMBER:  31737
SUBJECT: GRB 220306B: Nanshan/NEXT optical upper limit
DATE:    22/03/11 09:14:31 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>

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

We observed the field of Swift GRB 220306B (Caputo et al., GCN 31697) 
using the NEXT-0.6m telescope located at Nanshan, Xinjiang, China. We 
obtained 3x40 s and 1x60 s frames in the Sloan r-band, starting at 
18:23:35 UT on 2022-03-06, i.e., 478 s after the BAT trigger.

No optical source is detected at the Enhanced Swift/XRT position (Evans 
et al., GCN 31700) in our stacked image, down to a limiting magnitude of 
r~19.3, calibrated with the nearby PanSTARRS field.