Strong field effects on emission line profiles: Kerr black holes and warped accretion disks

TL;DR

This paper models emission line profiles from warped accretion disks around Kerr black holes, incorporating strong gravity effects, black hole spin, and disk warping, revealing complex features like multiple peaks and red tails.

Contribution

It extends relativistic line profile models to include black hole spin and disk warping, providing more accurate predictions of emission line features.

Findings

Multiple peaks in line profiles due to warping and spin effects

Long red tails and time variability linked to disk precession

Distorted disk images caused by strong gravitational lensing

Abstract

If an accretion disk around a black hole is illuminated by hard X-rays from non-thermal coronae, fluorescent iron lines will be emitted from the inner region of the accretion disk. The emission line profiles will show a variety of strong field effects, which may be used as a probe of the spin parameter of the black hole and the structure of the accretion disk. In this paper we generalize the previous relativistic line profile models by including both the black hole spinning effects and the non-axisymmetries of warped accretion disks. Our results show different features from the conventional calculations for either a flat disk around a Kerr black hole or a warped disk around a Schwarzschild black hole by presenting, at the same time, multiple peaks, rather long red tails and time variations of line profiles with the precession of the disk. We show disk images as seen by a distant observer, which are distorted by the strong gravity. Although we are primarily concerned with the iron K-shell lines in this paper, the calculation is general and is valid for any emission lines produced from a warped accretion disk around a black hole.