Soft X-ray Analysis

We developed and applied variability-assisted spectral analyses to soft X-ray energies (\(<\)3 keV) of Suzaku data sets of several types of active galactic nuclei; Mrk 509, Fairall 9, MCG-2-58-22 (type I Seyfert galaxies), 3C382 (broad line radio galaxy), 4C+74.26 (radio-loud quasar), and MR2251-178 (radio-quiet quasar). In all of them, the derived variable (and dominant) component had a power-law shape with a photon index of \(\sim \)1.8. The derived stationary component exhibited a much softer spectrum equivalent to a photo index of \(\sim \)4, and was confirmed to be essentially the same as the previously known “soft excess” component. On time scales of several weeks, however, this component exhibited slow variations (at least in Mrk 509), independently of the dominant variable emission with the photon index of \(\sim \)1.8. Therefore, the soft component is considered to be an additional primary emission, rather than a secondary component or contamination from the host galaxy. Interpreting the soft excess as thermal Comptonization emission, an electron temperature of \(\sim \)0.5 keV and an optical depth of \(\sim \)15 were obtained. Thus, the soft excess phenomenon is likely to be produced in a relatively cool and dense corona, which is clearly different form those producing the dominant power-law (with an electron temperature of more than 100 keV and an optical depth of less than 1.