GCN Circular 9761

D. Malesani, J.P.U. Fynbo (DARK/NBI), L. Christensen (ESO),
A. de Ugarte Postigo (OAB-INAF), B. Milvang-Jensen (DARK/NBI),
S. Covino (OAB-INAF) report on behalf of a larger collaboration

We have observed the afterglow of GRB 090809 (Markwardt
et al. GCNC 9754) using the X-shooter spectrograph mounted
at the Kueyen telescope of ESO's VLT (Paranal Observatory,
Chile) during its science verification phase. The spectrum,
consisting of a combined exposure of 4x1800s, was started
at 03:40 UT on August 09 (10.15 hrs after the burst). It was
obtained with an initial seeing of 0.9" and an airmass of
1.2, when the afterglow had a magnitude of R~21. The
spectrum covers the complete range from 3000 to 25000
Angstroms. In a preliminary analysis we identify the
Lyman break, Lyman-alpha, SiII, OI, SiI*, SiIV, CIV, FeII, AlII,
AlIII and MgII at a common redshift of 2.737 +/- 0.002 (pending
final wavelength calibration), which we identify as the redshift
of the GRB.

We thank the Paranal staff for excellent support, in particular
Elena Mason and Claudia Cid.