Line emission from optically thick relativistic accretion tori

TL;DR

This paper models line emission from relativistic accretion tori around Kerr black holes, analyzing how line profiles vary with viewing angle, black hole spin, and torus shape, and comparing them to thin disk emissions.

Contribution

It provides a detailed comparison of emission line profiles from relativistic tori and thin disks, highlighting the effects of geometry, inclination, and relativistic phenomena on observed spectra.

Findings

Line profiles from tori and disks share common features at low/moderate inclinations.

High inclination lines become broad and asymmetric, resembling single peaks.

Differences between torus and disk lines are mainly due to boundary radii and are prominent at high inclinations.

Abstract

We calculate line emission from relativistic accretion tori around Kerr black holes and investigate how the line profiles depend on the viewing inclination, spin of the central black hole, parameters describing the shape of the tori, and spatial distribution of line emissivity on the torus surface. We also compare the lines with those from thin accretion disks. Our calculations show that lines from tori and lines from thin disks share several common features. In particular, at low and moderate viewing inclination angles they both have asymmetric double-peaked profiles with a tall, sharp blue peak and a shorter red peak which has an extensive red wing. At high viewing inclination angles they both have very broad, asymmetric lines which can be roughly considered single-peaked. Torus and disk lines may show very different red and blue line wings, but the differences are due to the models for relativistic tori and disks having differing inner boundary radii. Self-eclipse and lensing play some role in shaping the torus lines, but they are effective only at high inclination angles. If inner and outer radii of an accretion torus are the same as those of an accretion disk, their line profiles show substantial differences only when inclination angles are close to 90 degrees, and those differences manifest mostly at the central regions of the lines instead of the wings.