Kavli Affiliate: Claudio Ricci
| First 5 Authors: Jeffrey McKaig, Claudio Ricci, Stéphane Paltani, K. K. Gupta, Nicholas P. Abel
| Summary:
Most Active Galactic Nuclei (AGN) in the local Universe are obscured. In
these obscured AGN an excess is usually observed in the soft X-rays below ~2
keV above 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 photoionised lines. Recent studies have found that in
highly obscured AGN this component has lower flux relative to the primary X-ray
continuum than in less obscured AGN. This is measured by the scattering
fraction, or fscatt, 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 fscatt are viewed at higher inclinations or
(2) low fscatt sources are characterized by larger covering factors. We
consider a conical NLR of free electrons, while allowing the column density and
opening angle (and hence covering 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 fscatt is expected to be
related to both the inclination angle and covering factor of the torus;
however, the observed negative correlation between fscatt and NH can only be
explained by a positive relation between the column density and the covering
factor of the obscuring material. Additional contributions to fscatt can come
from unresolved photoionised lines and ionised outflowing gas.
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