TITLE:   GCN CIRCULAR
NUMBER:  6260
SUBJECT: GRB 070406: Correction to the optical candidate in GCN6253
DATE:    07/04/08 08:47:20 GMT
FROM:    W.K. Zheng at NAOC  <zwk@bao.ac.cn>

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

We refined xinglong TNT data again, the candidate we
recommended before(GCN6253) may not be a real object
but a disturbance source due to CCD problem, we apologize
for this mistake and miss guidance.

We note there are several dark pixels at the CCD location
we mention before, and there is always a point-like source
at the same dark pixels of CCD positon in our white band 
image even thought the field has changed. To confirm this
we performed third epoach observation with multi-band about
41 hours after the burst. We did not detect the candidate
in all White, R, V bands, but in white bandat the dark
pixels postion there was still a faint point-like source.
Some subframs are avaliable at:
http://www.xinglong-naoc.org:8080/GRB070406/20h_W.fit
http://www.xinglong-naoc.org:8080/GRB070406/35h_W.fit
http://www.xinglong-naoc.org:8080/GRB070406/41h_W.fit
http://www.xinglong-naoc.org:8080/GRB070406/41h_R.fit
the source detected by Bloom et al.(GCN6259) may just be a
coincidence with the coordinat we mentioned before.

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