Discovery of very high energy gamma-ray emission from the BL Lac object
  PKS 0301-243 with H.E.S.S
  The active galactic nucleus PKS 0301-243 (z=0.266) is a
high-synchrotron-peaked BL Lac object that is detected at high energies (HE,
100 MeV < E < 100 GeV) by Fermi/LAT. This paper reports on the discovery of PKS
0301-243 at very high energies (E>100 GeV) by the High Energy Stereoscopic
System (H.E.S.S.) from observations between September 2009 and December 2011
for a total live time of 34.9 hours. Gamma rays above 200 GeV are detected at a
significance of 9.4{\sigma}. A hint of variability at the 2.5{\sigma} level is
found. An integral flux I(E > 200 GeV) = (3.3 +/- 1.1_stat +/- 0.7_syst)e-12 ph
cm^-2s^-1 and a photon index {\Gamma} = 4.6 +/- 0.7_stat +/- 0.2_syst are
measured. Multi-wavelength light curves in HE, X-ray and optical bands show
strong variability, and a minimal variability timescale of eight days is
estimated from the optical light curve. A single-zone leptonic synchrotron
self-Compton scenario satisfactorily reproduces the multi-wavelength data. In
this model, the emitting region is out of equipartition and the jet is particle
dominated. Because of its high redshift compared to other sources observed at
TeV energies, the very high energy emission from PKS 0301-243 is attenuated by
the extragalactic background light (EBL) and the measured spectrum is used to
derive an upper limit on the opacity of the EBL.
