Fe-K line probing of material around the AGN central engine with Suzaku
  We systematically analyzed the high-quality Suzaku data of 88 Seyfert
galaxies. We obtained a clear relation between the absorption column density
and the equivalent width of the 6.4 keV line above 10$^{23}$ cm$^{-2}$,
suggesting a wide-ranging column density of $10^{23-24.5}$ cm$^{-2}$ with a
similar solid and a Fe abundance of 0.7--1.3 solar for Seyfert 2 galaxies. The
EW of the 6.4 keV line for Seyfert 1 galaxies are typically 40--120 eV,
suggesting the existence of Compton-thick matter like the torus with a column
density of $>10^{23}$ cm$^{-2}$ and a solid angle of $(0.15-0.4)*4pi$, and no
difference of neutral matter is visible between Seyfert 1 and 2 galaxies. An
absorber with a lower column density of $10^{21-23}$ cm$^{-2}$ for Compton-thin
Seyfert 2 galaxies is suggested to be not a torus but an interstellar medium.
These constraints can be understood by the fact that the 6.4 keV line intensity
ratio against the 10--50 keV flux is almost identical within a range of 2--3 in
many Seyfert galaxies. Interestingly, objects exist with a low EW, 10--30 eV,
of the 6.4 keV line, suggesting that those torus subtends only a small solid
angle of $<0.2*4pi$. Ionized Fe-K$\alpha$ emission or absorption lines are
detected from several percents of AGNs. Considering the ionization state and
equivalent width, emitters and absorbers of ionized Fe-K lines can be explained
by the same origin, and highly ionized matter is located at the broad line
region. The rapid increase in EW of the ionized Fe-K emission lines at
$N_{H}>10^{23}$ cm$^{-2}$ is found, like that of the cold material. It is found
that these features seem to change for brighter objects with more than several
$10^{44}$ erg/s such that the Fe-K line features become weak. We discuss this
feature, together with the torus structure.
