[vsnet-grb-info 10863] GRB 110818A: Optical afterglow and redshift from VLT/X-shooter

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12284
SUBJECT: GRB 110818A: Optical afterglow and redshift from VLT/X-shooter
DATE:    11/08/19 07:49:47 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

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 
coordinates (J2000):

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 
observations.