2023MNRAS.526.5072M

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 ∼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 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 f_scatt 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 f_scatt is expected to be related to both the inclination angle and covering factor of the torus; however, the observed negative correlation between f_scatt and N_H can only be explained by a positive relation between the column density and the covering factor of the obscuring material. Additional contributions to f_scatt can come from unresolved photoionized lines and ionized outflowing gas.