Suzaku observation of the giant radio galaxy 3C 326
  A Suzaku observation of a giant radio galaxy, 3C 326, which has a physical
size of about 2 Mpc, was conducted on 2008 January 19 -- 21. In addition to
several X-ray sources, diffuse emission was significantly detected associated
with its west lobe, but the east lobe was contaminated by an unidentified X-ray
source WARP J1552.4+2007. After careful evaluation of the X-ray and Non X-ray
background, the 0.4 -- 7 keV X-ray spectrum of the west lobe is described by a
power-law model. The photon index and 1 keV flux density was derived as
$1.82_{-0.24}^{+0.26}\pm0.04$ and $19.4_{-3.2}^{+3.3}\pm 3.0$ nJy,
respectively, where the first and second errors represent the statistical and
systematic ones. The diffuse X-rays were attributed to be inverse Compton
radiation by the synchrotron radio electrons scattering off the cosmic
microwave background photons. This radio galaxy is the largest among those with
lobes detected through inverse Compton X-ray emission. A comparison of the
radio to X-ray fluxes yields the energy densities of electron and magnetic
field as $u_e = (2.3 \pm 0.3 \pm 0.3) \times 10^{-13}$ ergs/cm3 and $u_m =
(1.2_{-0.1}^{+0.2}\pm 0.2) \times 10^{-14}$ ergs/cm3, respectively. The galaxy
is suggested to host a low luminosity nucleus with an absorption-corrected 2 --
10 keV luminosity of $<2 \times 10^{42}$ ergs/s, together with a relatively
weak radio core. The energetics in the west lobe of 3C 326 were compared with
those of moderate radio galaxies with a size of $\sim 100$ kpc. The west lobe
of 3C 326 is confirmed to agree with the correlations for the moderate radio
galaxies, $u_e \propto D^{-2.2\pm0.4}$ and $u_m \propto D^{-2.4\pm0.4}$, where
$D$ is their total physical size. This implies that the lobes of 3C 326 are
still being energized by the jet, despite the current weakness of the nucleus.
