GCN Circular 7117

P. Jakobsson (Univ. Hertfordshire), J.P.U. Fynbo, D. Malesani 
(DARK/NBI), N.R. Tanvir (Univ. Leicester), B. Milvang-Jensen (DARK/NBI), 
A.O. Jaunsen (Univ. Oslo), P.M. Vreeswijk, J. Hjorth (DARK/NBI), report 
on behalf of a larger collaboration:

We observed the field of GRB 071117 (Ukwatta et al., GCN 7098
Not found
 
 
) with the 
ESO VLT, starting on 2007 Nov 18.005 UT (9.28 hr after the GRB). We 
clearly detect the two sources indicated by Bloom (GCNs 7105
Not found
 
 
, 7110
Not found
 
 
), 
including the afterglow s2. Source s1 appears extended in our images, 
while source s2 is indeed pointlike (seeing 0.85"). A faint nebulosity 
is apparent surrounding both objects.

A VLT spectrum was obtained with the FORS1 instrument starting on 2007 
Nov 18.03 UT, placing both sources on the slit. Three exposures of 30 
min each were secured. The afterglow spectrum shows a faint, blue 
continuum between 3700 to 9000 A, and a weak emission line is apparent 
at 8688 A. Interpreting this as [OII], we infer a redshift of z=1.331, 
which we consider as the likely redshift of the GRB. Interpreting the 
observed line as [OIII] or Halpha, we would expect to detect [OII] at 
6466 or 4934 A, respectively, which we do not see. A more conservative 
upper limit to the GRB redshift comes from the nondetection of any 
dropout in the blue down to 3800 A, which implies z < 2.1.

The spectrum of s1 is very red, with no significant flux below 5000 A. A 
plot of the 2D spectrum and a finding chart showing the afterglow and 
the various XRT error circles is posted at:

https://grbtoo.dark-cosmology.dk/public/gcn-pages/grb-071117/

We acknowledge excellent support from the ESO observing staff, in 
particular Stephane Brillant and Emanuela Pompei.