Relativistic emission lines from accreting black holes - The effect of disk truncation on line profiles

TL;DR

This paper models relativistic emission lines from accretion disks around rotating black holes, examining how disk truncation and various velocity profiles influence line shapes, aiding interpretation of X-ray observations.

Contribution

It introduces a generalized kinematic model including radial drifts and non-Keplerian rotations, and explores how disk truncation affects emission line profiles near black holes.

Findings

Radial drift reduces the red wing flux of emission lines.

Line profiles can be classified into several types including triangular and shoulder-like.

Truncated accretion disks can produce characteristic shoulder-like profiles matching observations.

Abstract

Relativistic emission lines generated by thin accretion disks around rotating black holes are an important diagnostic tool for testing gravity near the horizon. The iron K-line is of special importance for the interpretation of the X-ray emission of Seyfert galaxies, quasars and galactic X-ray binary systems. A generalized kinematic model is presented which includes radial drifts and non-Keplerian rotations for the line emitters. The resulting line profiles are obtained with an object-oriented ray tracer operating in the curved Kerr background metric. The general form of the Doppler factor is presented which includes all kinds of poloidal and toroidal motions near the horizon. The parameters of the model include the spin parameter, the inclination, the truncation and outer radius of the disk, velocity profiles for rotation and radial drift, the emissivity profile and a multi-species line-system. The red wing flux is generally reduced when radial drift is included as compared to the pure Keplerian velocity field. All resulting emission line profiles can be classified as triangular, double-horned, double-peaked, bumpy and shoulder-like. Of particular interest are emission line profiles generated by truncated standard accretion disks (TSD). It is also shown that the emissivity law has a great influence on the profiles. The characteristic shoulder-like line profile observed for the Seyfert galaxy MCG-6-30-15 can be reproduced for suitable parameters