[vsnet-grb-info 27428] GRB 210218A： GWAC-F60A optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29531
SUBJECT: GRB 210218A： GWAC-F60A optical upper limit 
DATE:    21/02/18 14:42:03 GMT
FROM:    Liping Xin at NAOC, SVOM  <xlp at nao.cas.cn>

L. P. Xin(NAOC),  J. Wang(GXU), C. Gao(GXU), X. H. Han(NAOC), J. Y. Wei(NAOC), 
G. W. LI(NAOC),  L. H. Li(NAOC), C. Wu(NAOC),  X. G. Wang(GXU), 
E. W. Liang (GXU), R. S. Zhang(NAOC), Y. L. Qiu(NAOC), 
and J. S. Deng(NAOC) report: 

We began to observe GRB 210218A (Sbarufatti al., GCN 29529)
with Xinglong GWAC-F60A telescope, China, at 11:37:45 (UT), 
18th. Feb. 2021, about 146 sec after the burst, under bad seeing condition. 

A series of  R, I images were obtained.
Preliminary analysis shows that no any new optical source
was found in single images within the Swift errorbox (Sbarufatti al., GCN 29529), 
down to the 3 sigma upper limit of 15.0 mag in R band.
The upper limit is calibrated to the USNO B1.0 catalog.

This result is consistent with the previous report (Zhu et al., GCN 29530).