Giant Lobes of Centaurus A Radio Galaxy Observed with the Suzaku X-ray
  Satellite
  [abridged] We report on Suzaku observations of selected regions within the
Southern giant lobe of the radio galaxy Centaurus A. We focus on distinct X-ray
features likely associated with fine radio structure of the lobe. We find that
the spectral properties of the detected X-ray features are equally consistent
with thermal emission from hot gas, or with a power-law radiation continuum.
However, the plasma parameters implied by these different models favor a
synchrotron origin for the analyzed X-ray spots, indicating that a very
efficient acceleration of electrons is taking place within the giant structure
of Centaurus A, albeit only in isolated and compact regions. We also present a
detailed analysis of the diffuse X-ray emission, resulting in a tentative
detection of a soft excess component best fitted by a thermal model with a
temperature of 0.5 keV. The exact origin of the observed excess remains
uncertain, although energetic considerations point to thermal gas filling the
bulk of the volume of the lobe and mixed with the non-thermal plasma. The
corresponding pressure of the thermal gas in such a case appears to be in
almost exact equipartition with the pressure provided by the radio-emitting
electrons and the magnetic field. Although tentative, our findings potentially
imply that the structure of the extended lobes in active galaxies is likely to
be highly inhomogeneous, with magnetic reconnection processes continuously
converting magnetic energy to internal energy of the plasma particles, leading
to spatial and temporal variations in the plasma parameters around the
equilibrium condition.
