D. Xu (DARK/NBI), P. M. Vreeswijk (Weizmann), J. P. U. Fynbo
(DARK/NBI), V. D'Elia (ASI/ASDC and INAF/Roma), K. Wiersema,
N. R. Tanvir (Univ. Leicester), A. de Ugarte Postigo (IAA-CSIC),
S. Covino (INAF/OAB) report on behalf of a larger collaboration:
We observed the optical afterglow of the Swift GRB 141109A (D'Avanzo
et al., GCN 17037), using the X-shooter spectrograph at ESO's
VLT. Observations started at 07:45 UT on 2014 Nov 9 (1.9 hr after the
GRB), and consisted of 2x1200 s exposures in each of the UVB, VIS, and
NIR arms, covering the wavelength range 3000-20,000 AA.
In the acquisition image, we detect a point source, which is not
detected in the SDSS, at the position (J2000):
RA = 09:38:07.44
Dec = -00:36:29.9
with an uncertainty of about 0.5". This position is consistent with
that of the NIR afterglow reported by Covino et al. (GCN 17039). We
measure a (preliminary) magnitude of R=19.2+-0.1 (Vega).
We detect a variety of absorption features throughout the entire
spectrum. In particular, a wide trough is visible centered around 4800
AA, which we interpret as due to H I absorption at redshift z~3.
Identification of several metal features as due to, among others, Si
II, C II, Fe II, C IV, SiIV, allows us to refine the value to
z=2.993. The presence of several fine structure lines of Fe II, Si II,
O I, Ni II and C II confirms this is the redshift of the GRB.
We note the presence of two strong intervening system at z ~ 1.67 and
z ~ 2.5 (detected in Mg II).
We acknowledge excellent support from the ESO observing staff at
Paranal, in particular Valentin Ivanov and Marcelo Lopez. We also
thank the visiting astronomer Simone Zaglia from the ESO-GAIA survey,
who made these observation possible.