GCN Circular 9015

A. de Ugarte Postigo, S. D�Odorico (ESO PI), J. Vernet, A. Modigliani,
S. Ramsay from ESO Commissioning team;
S. Covino (INAF Brera), H. Flores (Obs. Paris), J. Fynbo, J. Hjorth
(NBI/DARK, U. Copenhagen) and R.A.M.J. Wijers (Astr. Institute,
U. Amsterdam) from the X-shooter GRB team;
F. Hammer (Obs. Paris), L. Kaper (Astr. Institute, U. Amsterdam),
P. Kjaergaard (NBI, U. Copenhagen), S. Randich (INAF Arcetri) as
X-shooter PIs;
P.J. Groot (Radboud Univ. Nijmegen) from the X-shooter Science Team.

On March 15.22 UT we initiated observations of GRB 090313 (Chornock
et al., GCNC 8979; Mao et al., GCNC 8980) with X-shooter at the ESO
Melipal telescope of the Paranal Observatory. X-shooter is the first
of the second-generation VLT instruments and includes three
Echelle spectrographs, the Ultraviolet/Blue (UVB), the Visible (VIS)
and the Near Infrared (NIR), which combined provide a fixed spectral
format and cover in one shot the spectral range 3000 - 24000 A at
medium spectral resolution (R = 4000 - 10000 depending on the arm
and slit width). The mean epoch of the observation was 45.3 hours
after the burst, when the afterglow had faded to R ~ 21.6 (Perley et
al. GCNC 9001; Cobb et al. GCNC 9008). In the 4 x 1500 s combined
spectrum we clearly detect continuum above 5580 A with several
absorption lines; below this, the signal is dominated by background
emission produced by the nearby Moon (90 % illumination at 37 deg
from the field). The spectrum indicates an absorption redshift
of z = 3.3721 � 0.0004 (consistent with that measured by Chornock et
al., GCNC 8994 and Thoene et al., GCNC 9012) through the detection of
Si II (1304.5), C II (1334.5), Si IV (1393.8), Si IV (1402.8), Si II
(1526.7), C IV (1548.2,1550.8), Fe II (1608.5), Fe II (1611.2),
Al III (1854.7), Al III (1862.8), Zn II (2062.6), Fe II (2600.1),
Mg II (2796.3, 2803.5) and Mg I (2853.0). The intervening system
identified by Thoene et al. (GCNC 9012) is resolved into multiple
components through the detection of Fe II, Mg II and Mg I lines with
its main absorption at redshift 1.800. A further system at z = 1.959
shows Fe II, Mg II and Mg I absorption.

The spectra of GRB 090313 will be made public on the ESO web as other
data of scientific relevance obtained during the commissioning of the
instrument.

[GCN OPS NOTE923mar09): Per author's request, the Groot-author's
affiliation was changed.]