Comparison of hard X-ray spectra of luminous radio galaxies and their
  radio-quiet counterparts
  We study the differences in X-ray properties of luminous radio galaxies and
their radio-quiet counterparts. In order to avoid biases associated with the
dependence of X-ray properties on the black hole mass and Eddington ratio, the
radio-loud and radio-quiet objects are selected to cover similar ranges of
these parameters. Our studies are based on the X-ray data from the Swift/BAT
catalogue. We confirm previous results that radio galaxies are on average
X-ray-louder than radio-quiet AGNs, but find that their spectral slopes are
very similar. This suggests that in radio-loud and radio-quiet AGNs the hard
X-rays are produced in the same region and by the same mechanism. We argue that
this region can be associated with the hot, geometrically thick, central
portion of the accretion flow, where production of hard X-rays is likely to be
dominated by Comptonization of the optical/UV radiation of the truncated 'cold'
accretion disc by hot electrons. The larger X-ray luminosities in radio-loud
AGNs may result from larger radiative efficiencies of the innermost portions of
the accretion flows around faster rotating black holes.
