Probing the active galactic nuclei (AGN) torus structure using X-ray spectral variability.
Abstract
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), atsub-pc scales, and thereby fuels the central engines of activegalactic nuclei (AGN). Circumnuclear structures such as the cold,dusty "torus" are believed to be an active step in SMBH accretion, butthe nature and structure of the torus in AGN is still highly debated,with various theoretical models encompassing continuous or clumpydistributions. A further complication is potential absorption from host galaxystructures. A major probe of morphology and location of line of sight gas is thevariable absorption detected in the 0.3-10 keV X-ray spectra.Here, we present the latest results from an extensive X-ray spectralvariability study of a sample of 20 perpetually-absorbed Compton-thintype IIs using XMM, Chandra, Suzaku and NuSTAR. In some objects, namely most low-N_H targets, our findings support thenotion that X-ray absorption is not necessarily indicative of acompact, pc-scale torus; host galaxy structures at kpc scales likelycontribute. In other objects, the high and non-variable value of N_H suggests amostly smooth, continuous torus. We add to the evidence of clumpy structures at << pc scales: we notepartial-covering structures sustained across nearly half thesample. In addition, we find evidence for clumpy or inhomogeneousfull-covering compact structures in five additional sources. In conclusion, we cannot assign a common source of X-ray absorptionacross the sample. We thus urge caution in drawing conclusions about the properties ofthe compact torus without properly accounting for the absorption contribution from thehost galaxy.
- Publication:
-
AAS/High Energy Astrophysics Division
- Pub Date:
- March 2019
- Bibcode:
- 2019HEAD...1710640L