The X-ray spectra of accreting Kerr black holes

TL;DR

This paper reviews X-ray spectra of accreting Kerr black holes, emphasizing relativistic iron lines, reflection features, and gravitational effects, suggesting rapid black hole spin and common spectral components in active galactic nuclei and black hole systems.

Contribution

It provides a comprehensive review of spectral features indicating black hole spin and reflection processes, highlighting the role of relativistic effects in X-ray observations.

Findings

Relativistic broad iron lines suggest black hole spin.

Reflection features are common in accreting black holes.

Gravitational bending explains spectral variability.

Abstract

The relativistic broad iron lines seen in the X-ray spectra of several active galaxies and Galactic black hole systems are reviewed. Most such objects require emission from within the innermost stable orbit of a non-rotating black hole, suggesting that the black holes are rapidly spinning Kerr holes. We discuss the soft excess, the broad iron line and the Compton hump characteristic of reflection from partially ionized gas and show that they may be a common ingredient in the X-ray spectra of many radiatively-efficient, accreting black holes. Strong gravitational bending of the radiation close to a Kerr black hole can explain the otherwise puzzling spectral variability seen in some objects. The Narrow Line Seyfert 1 galaxies may be among the most extreme objects yet seen.