Are Compton-thin AGNs Globally Compton Thin?

TL;DR

This study investigates whether AGNs classified as Compton-thin based on line-of-sight measurements are also globally Compton-thin, using broadband X-ray spectra modeling to reveal some are actually Compton-thick in their overall structure.

Contribution

The paper introduces a self-consistent modeling approach with MYTORUS to measure global column densities, revealing that some AGNs are globally Compton-thick despite appearing Compton-thin along the line of sight.

Findings

Some AGNs are globally Compton-thick with N_H > 1.5 x 10^{24} cm^{-2}.

Most Fe Kα lines are narrow, not relativistically broadened.

The global column density can differ significantly from the line-of-sight measurement.

Abstract

We select eight nearby AGNs which, based on previous work, appear to be Compton-thin in the line of sight. We model with MYTORUS their broadband X-ray spectra from 20 individual observations with $Suzaku$, accounting self-consistently for Fe K$\alpha$ line emission, as well as direct and scattered continuum from matter with finite column density and solar Fe abundance. Our model configuration allows us to measure the global, out of the line of sight, equivalent hydrogen column density separately from that in the line of sight. For 5 out of 20 observations (in 3 AGNs) we find that the global column density is in fact $\gtrsim 1.5 \times 10^{24}$cm$^{-2}$, consistent with the distant scattering matter being Compton-thick. For a fourth AGN, 2 out of 5 observations are also consistent with being Compton-thick, although with large errors. Some of these AGNs have been reported to host relativistically broadened Fe K$\alpha$ emission. Based on our modeling, the Fe K$\alpha$ emission line is not resolved in all but two $Suzaku$ observations, and the data can be fitted well with models that only include a narrow Fe K$\alpha$ emission line.