Probing the active galactic nuclei (AGN) torus structure using X-ray spectral variability.

It is still a big puzzle as to how the host galaxy gas (at kpc scales) feeds the accretion disk of a supermassive black hole (SMBH), at sub-pc scales, and thereby fuels the central engines of active galactic nuclei (AGN). Circumnuclear structures such as the cold, dusty "torus" are believed to be an active step in SMBH accretion, and understanding the structure of this medium is essential for understanding disk/SMBH fueling. However, the torus structure is still highly debated, with various theoretical models encompassing continuous or clumpy distributions. A major probe of the torus' properties is the variable absorption detected in the 0.3-10 keV X-ray spectra, which serves to probe the torus' morphology and location. Here, we present the latest results from an extensive X-ray spectral variability study of a sample of 20 Compton-thin Seyfert 2 galaxies using XMM, Chandra, Suzaku and NuSTAR. The column density variations (or lack thereof) enable us to probe various torus morphology scenarios and to also consider possible host galaxy contributions to total absorption.