P. D'Avanzo (INAF/Brera), M. Sparre, D. Watson, J. P. U. Fynbo, D.
Malesani, B. Milvang-Jensen (DARK/NBI), P. Goldoni (APC/Univ. Paris 7
and SAp/CEA), V. D'Elia (INAF/Rome), and N. R. Tanvir (U. Leicester),
report on behalf of the X-shooter GTO GRB collaboration:
We observed the field of GRB 110818A (Markwardt et al. GCN 12279) with
the ESO VLT equipped with X-shooter. Observations started on 2011-08-19
at 02:47 UT (6.15 hr after the GRB).
The acquisition image shows an optical afterglow candidate inside the
XRT error circle (Markwardt et al. GCN 12279) at the following
RA = 21:09:21.04
Dec = -63:58:52.3
with an uncertainty of about 0.5". The object has a magnitude R ~ 22.3,
calibrated assuming R = 19.2 for the USNO-B1 star 0260-0726657 (RA, Dec
= 21:09:23.14, -63:58:33.0).
A total spectroscopic exposure of 4x1200 s was obtained, covering the
spectral range from 300 to 2500 nm.
We report a redshift of z = 3.36 based on detection of absorption
features from Si II, C IV, Al II, Ca H, Ca K and Mg I. Emission from the
[O III] doublet is also observed.
We would like to thank the staff at the VLT, in particular, Alain
Smette, Patricia Guajardo and Dimitri Gadotti for carrying out the