Reprocessed emission from warped accretion discs with application to X-ray iron line profiles

Abstract

Flourescent iron line profiles currently provide the best diagnostic for active galactic nuclei (AGN) engine geometries. Here we construct a method for calculating the relativistic iron line profile from an arbitrarily warped accretion disc, illuminated from above and below by hard X-ray sources. This substantially generalises previous calculations of reprocessing by accretion discs by including non-axisymmetric effects. We include a relativistic treatment of shadowing by ray-tracing photon paths along Schwarzchild geodesics. We apply this method to two classes of warped discs, and generate a selection of resulting line profiles. New profile features include the possibility of sharper red, and softer blue fall-offs, a time varying line profile if the warp precesses about the disc, and some differences between `twisted' and `twist-free' warps. We discuss some qualitative implications of the line profiles in the context of Type I and II Seyfert AGN.