TITLE: GCN CIRCULAR NUMBER: 6424 SUBJECT: GRB 070520: Xinglong EST optical Upper Limit DATE: 07/05/20 15:06:24 GMT FROM: L.P. Xin at NAOC L.P. Xin, M.Zhai, Y.L. Qiu, J.Y. Wei, J.Y. Hu, J.S. Deng, Y. Urata, and W.K. Zheng on behalf of EAFON report: We have imaged the field of GRB 070520 (P. Romano et al., GCN 6423) with the EST 1m telescope at Xinglong Observatory? Observation started from 13:14:54 UT, 579s after the burst with R band filter, we derieved 3 sigam limit is ~20.6 in our 20*60s co-added images withmean time ~20minutes. This message may be cited.