Hard X-ray Analysis

We applied variability-assisted spectral analyses which we developed in Chap. 3 to hard X-ray energies (3–45 keV) of Suzaku data sets of several active galactic nuclei, including NGC 3516, NGC 3227, NGC 4051, MCG–6-30-15, Mrk 841, NGC 5548, and IC4329A. In all these active galactic nuclei, the derived variable component had a weakly absorbed power-law shape with a photon index of 1.7–2.2. The derived stationary components exhibited intense narrow Fe-K lines, with various continuum shapes. In some cases, it was well explained solely as reflection signals from a distant/neutral accretion disk or a torus, while in other cases, it also included an additional featureless harder (a photon index = 1.4–1.7) continuum with strong absorption (a column density is about \(10^{23}\) cm\(^{-2}\)). It sometimes bears the Fe-K edge feature, but is not accompanied by Fe-K emission lines. In NGC 3516, this additional harder emission was observed on one occasion, and disappeared in the other observation when the source became fainter. In NGC 3227, inversely, the harder component was always present with slow intensity changes, while the rapidly variable steeper power-law disappeared when the source became fainter. Since the two featureless continua, namely the rapidly variable steeper one and the slowly varying harder/absorbed one, thus vary without correlation,we regard both of them as the primary emission from the central engine.