Ray-tracing simulations of the soft X-ray scattered emission in obscured active galactic nuclei

Most active galactic nuclei (AGNs) in the local Universe are obscured. In these obscured AGNs, an excess is usually observed in the soft X-rays below similar to 2 keV abo v e the absorbed X-ray continuum. This spectral component is associated with the scattering of X-ray photons off free electrons in the narrow-line region (NLR), and/or to photoionized lines. Recent studies have found that in highly obscured AGNs this component has lower flux relative to the primary X-ray continuum than in less obscured AGNs. This is measured by the scattering fraction, or f(scatt), which is the ratio of the scattered flux to the continuum. Here, we use the ray-tracing platform REFLEX to perform simulations of scattered X-ray radiation to test two possible explanations for this phenomenon: (1) sources with lower f(scatt) are viewed at higher inclinations or (2) low fscatt sources are characterized by larger co v ering factors. We consider a conical NLR of free electrons, while allowing the column density and opening angle (and hence co v ering factor) to vary. We also consider electron densities inferred from observations, and from simulations carried out with the spectral synthesis code CLOUDY . Our simulations show f(scatt) is expected to be related to both the inclination angle and co v ering factor of the torus; ho we v er, the observ ed ne gativ e correlation between f(scatt )and NH can only be e xplained by a positiv e relation between the column density and the co v ering factor of the obscuring material. Additional contributions to f(scatt) can come from unresolved photoionized lines and ionized outflowing gas.