Optical spectroscopy of the gamma-ray bright blazars PKS 0447-439 and
  PMN J0630-24
  The large majority of sources detected by the Fermi Gamma-ray Space Telescope
are blazars, belonging in particular to the blazar subclass of BL Lacertae
objects (BL Lacs). BL Lacs often have featureless optical spectra, which make
it difficult and sometimes impossible to determine their redshifts. This
presents a severe impediment for the use of BL Lacs to measure the spectrum of
the extragalactic background light through its interaction with high-energy
gamma-ray photons. I present here high-quality optical spectroscopy of two of
the brightest gamma-ray blazars, namely, PKS 0447-439 and PMN J0630-24. The
medium-resolution and high signal-to-noise ratio optical spectra show clear
absorption lines, which place these BL Lacs at relatively high redshifts of
z>=1.246 for PKS 0447-439 and z>=1.238 for PMN J0630-24.
