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Strong field gravity and spin of black holes from broad iron lines

Published online by Cambridge University Press:  11 April 2011

A. C. Fabian
Affiliation:
University of Cambridge, UK
Mario Livio
Affiliation:
Space Telescope Science Institute, Baltimore
Anton M. Koekemoer
Affiliation:
Space Telescope Science Institute, Baltimore
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Summary

Accreting black holes often show iron line emission in their x-ray spectra. When this line emission is very broad or variable, it is likely to originate from close to the black hole. The theory and observations of such broad and variable iron lines are briefly reviewed here. In order for a clear broad line to be found, one or more of the following have to occur: high iron abundance, dense disk surface and minimal complex absorption. Several excellent examples are found from observations of Seyfert galaxies and Galactic Black Holes. In some cases there is strong evidence that the black hole is rapidly spinning. Further examples are expected as more long observations are made with XMM-Newton, Chandra and Suzaku. The x-ray spectra show evidence for the strong gravitational redshifts and light bending expected around black holes.

Introduction

Most of the radiation from luminous accreting black holes is released within the innermost 20 gravitational radii (i.e., 20rg = 20 GM/c2). In such an energetic environment, iron is a major source of x-ray line emission, with strong emission lines in the 6.4–6.9 keV band. Observations of such line emission provides us with a diagnostic of the accretion flow and the behavior of matter and radiation in the strong gravity regime very close to the black hole (Fabian et al. 2000; Reynolds & Nowak 2003; Fabian & Miniutti 2009; Miller 2007).

The rapid x-ray variability found in many Seyfert galaxies is strong evidence for the emission orginating at small radii.

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Chapter
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Black Holes , pp. 182 - 190
Publisher: Cambridge University Press
Print publication year: 2011

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