Presentation #100.11 in the session AGN.
Active galactic nuclei (AGN) are powered by accreting supermassive black holes, surrounded by a torus of obscuring material. The exact geometry of this material has been a subject of debate, as models have advanced from the initial homogeneous torus to a variety of possibilities, ranging from cloud distributions, to warped disks, to outflows. It is clear, however, that this distribution is clumpy: X-ray determinations of line-of-sight (l.o.s.) obscuration show variability on timescales from <1 day to years. X-ray observations remain the only way to probe the obscuring column density in the line of sight at any given time, and thus the optimal tool to place constraints on the exact distribution of this material.
In this work, we present a multi-epoch X-ray analysis of 12 local obscured AGN, including a total of 85 X-ray observations, spanning more than 20 yrs of observing time. Our analysis shows l.o.s. column density variability for 7/12 sources. Surprisingly, we observe large differences between l.o.s. column densities and average torus column densities for most sources. This suggests that the material responsible for obscuration and reflection is not the same, pointing toward added complexities in the torus structure. We also conclude that variable sources tend to have higher obscuration in average (i.e. denser tori), and broader cloud distributions.