TITLE:   GCN CIRCULAR
NUMBER:  22804
SUBJECT: GRB 180618A: Xinglong-2.16m optical upper limit
DATE:    18/06/20 13:02:02 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>

Z.P. Zhu, D. Xu, J.B. Zhang (NAOC), X. Zhang, J.H. Liu (XAO), Z.B. Dai 
(YNAO) report:

We observed the field of GRB 180618A (LaPorte et al., GCN 22790) using 
the 2.16-m telescope located at Xinglong, Hebei, China, equipped with 
the BFOSC camera. We obtained 6x600s R-band frames, starting at 12:43:22 
UT on 2018-06-19, i.e., 1.50 days after the BAT trigger.

The previously detected optical afterglow of the GRB (e.g., LaPorte et 
al., GCN 22790; Guidorzi et al., GCN 22792; Tyurina et al., GCN 22797) 
was not present in our stacked image, down to a limiting magnitude of 
R~21.4 mag, calibrated with the SDSS field.