[vsnet-grb-info 2021] VLT/UVES spectroscopy of GRB050820

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3860
SUBJECT: VLT/UVES spectroscopy of GRB050820
DATE:    05/08/23 10:29:02 GMT
FROM:    Paul Vreeswijk at ESO  <pvreeswi at eso.org>

C. Ledoux, P. Vreeswijk (ESO), S. Ellison (U. Victoria), A. Jaunsen
(ESO/U. Oslo), A. Smette (ESO), J. Fynbo (U. Copenhagen), P. Moller,
A.  Kaufer (ESO), M. Andersen (AIP), R. Wijers (U. Amsterdam) &
J. Hjorth (U. Copenhagen) report:

We observed the afterglow (Fox & Cenko, GCN 3829) of GRB 050820 (Page
et al, GCN 3830) with UVES at VLT/UT2, starting at 7:08 UT (33 minutes
after the burst trigger). The spectra cover most of the optical
wavelength range (split into two observations of a total of 60min
using one dichroic beam splitter and 40min using the other), with an
approximate resolving power of 46,000 (6.5 km/s).

We obtain a redshift of z=2.6147 (and therefore confirm the redshift
reported by Prochaska et al., GCN 3833) from the detection of numerous
host-galaxy metal absorption lines (e.g., CII, CIV, NI, OI, AlII,
AlIII, SiII, SiIV, SII, ArI, CrII, FeII, NiII, ZnII) spread over a
velocity interval of ~400 km/s. Strong fine-structure lines of CII*
and SiII* are also detected. We measure a total neutral hydrogen
column density of log N(HI)=21.0 and metallicities of [Si/H]=-0.6 and
[Fe/H]=-1.1.

In addition, an intervening metal absorption line system with log
N(HI)=20.0 is observed at zabs=2.3597.

We acknowlegde the excellent support from the ESO staff, and in
particular the alertness of night astronomer Stefano Bagnulo.