TITLE:   GCN CIRCULAR
NUMBER:  6965
SUBJECT: GRB071018: 2nd epoch obsevations of Xinglong TNT
DATE:    07/10/21 18:24:51 GMT
FROM:    L.P. Xin at NAOC  <xlp@bao.ac.cn>

L.P. Xin, M. Zhai, Y.L. Qiu, J.Y. Wei, J.Y. Hu, J.S. Deng,
J. Wang, Y. Urata and W.K. Zheng on behalf of EAFON report:

We observed the field of GRB071018 (Krim et al. GCN 6932) with the TNT 0.8m 
telescope at Xinglong Observatory for the 2nd epoch, Observation was started 
from 19:12:25 UT, 19th Oct. 1.494 days after the burst. A series of R-band 
images were obtained. In our 14*600s combined images we can still find the 
two sources of our last observation (Xin et al. GCN 6936). 

The estimated bringhtness of the source #1 and #2 (Xin et al. GCN6936) 
derieved from USNO-B1.0 R2 magnitude were R=20.67+-0.318 and R=20.72+-0.36 
respectively. The magnitude of source #1 was consistent with the value 
reported by SARA (Updike et al. GCN 6944) and Mercator (Alberto 
Castro-Tirado, GCN6947). but bringter than the value of our last observation 
(Xin et al. GCN6936), So the source #1 only maybe a avariable source as 
reported (Adria, GCN 6944), and the source $2 also might not be the OT of the 
burst.

At the locations of the XRT error circles of source 1 and source 2 (GCN 6943, 
Beardmore et al.), We found no new optical source to the 3sigma limit  
magnitude R=21.2 . 

We also checked the combined image (Xin et al. GCN6936) obtained on 18th Oct, 
No new source was found at the location of XRT source 2 to 3-sigma limit 
magnitude R=21.5. The location of XRT source 1 was outside the field of view 
of the combined image.

This massage may be cited.