TITLE:   GCN CIRCULAR
NUMBER:  16983
SUBJECT: GRB 141028A: VLT/X-shooter redshift of z=2.33
DATE:    14/10/29 08:15:25 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani@dark-cosmology.dk>

D. Xu (DARK/NBI), A. J. Levan (Univ. Warwick), J. P. U. Fynbo 
(DARK/NBI), N. R. Tanvir (Univ. Leicester), V. D'Elia (ASI/ASDC and 
INAF/Roma), D. Malesani (DARK/NBI), report on behalf of a larger 
collaboration:

We observed the optical afterglow (Gorbovskoy et al., GCN 16972; Graham 
et al., GCN 16977) of the Fermi/LAT GRB 141028A (Roberts, GCN 16971; 
Bissaldi et al., GCN 16969; Hurley et al., GCN 16975), using the 
X-shooter spectrograph at the ESO VLT. Observations started at 02:15 UT 
on 2014 Oct 29 (15.35 hr after the GRB), and consisted of 4x600 s 
exposures in each of the UVB, VIS, and NIR arms, covering the wavelength 
range 3000-25,000 AA.

We detect a variety of absorption features throughout the entire 
spectrum. In particular, a wide trough is visible centered around 4050 
AA, which we interpret as due to H I absorption at redshift z = 2.33. 
Identification of several metal features as due to, among others, Si II, 
C II, Fe II, C IV, Mg II, allows us to refine the value to z = 2.332.

We note the presence of a strong intervening system at z = 1.823 
(detected e.g. in C IV, Fe II, Mg II), and a weaker one at z = 2.09 (C 
IV). The former coincides with the system reported by Cucchiara et al. 
(GCN 16982).

We acknowledge excellent support from the ESO observing staff at 
Paranal, in particular Cedric Ledoux and Dimitri Gadotti.