Variability: A X-ray ruler for the AGN structure model

XMM-Newton Science Operations Centre, European Space Astronomy Centre of ESA, Camino bajo del Castillo, s/n Urbanización Villafranca del Castillo Villanueva de la Cañada, 28692 Madrid, Spain

Abstract

Validating our understanding of the innermost structure of Active Galactic Nuclei (AGN) would require resolving sub-parsec scales. Lacking adequate direct imaging, X-ray astronomy can still contribute to this undertaking through the study of spectral variability on time-scales from days to years. This bears information on the location of gaseous and dusty systems in the innermost regions around the accreting supermassive black hole. In this paper I discuss the application of this concept in two specific contexts: a) “fast” column density variations in heavily obscured AGN; b) reverberation of optically-thick reprocessing. These results lend support to a scenario where obscuration and optically thick reprocessing are due to a variety of different systems, ranging from the Broad Line Regions to a clumpy structure extended on larger scales up to hundreds of parsecs.