* Astronomy

Title: On the redshift of the bright BL Lac object PKS 0048-097
Authors: Marco Landoni, Renato Falomo, Aldo Treves, Boris Sbarufatti, Roberto Decarli, Fabrizio Tavecchio, Jari Kotilainen

Aims: The determination of elusive redshifts of bright BL Lac objects
Methods: We use the capabilities of newly available spectrograph X-Shooter at European Southern Observatory (ESO) Very Large Telescope, that combines high resolution and a large wavelength range, to obtain UVB to near-IR spectra of BL Lacs.
Results: Our observations of PKS 0048-097 detect three emission lines that permit to derive a redshift z = 0.635. Moreover, a Mg II absorption system at z = 0.154 that is associated with a foreground spiral galaxy at 50 Kpc projected distance is found.
Conclusions: The obtained redshift allows us to comment about the optical beaming factor and the absorption of the high energy spectrum by the Extragalactic Background Light.

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