Gravitational effects on the high energy emission of accreting black holes

Free access article

Issue		A&A Volume 453, Number 3, July III 2006


Page(s)		773 - 783
Section		Astrophysical processes
DOI		http://dx.doi.org/10.1051/0004-6361:20064973

A&A 453, 773-783 (2006)
DOI: 10.1051/0004-6361:20064973

Gravitational effects on the high energy emission of accreting black holes

T. Suebsuwong, J. Malzac, E. Jourdain and A. Marcowith

Centre d'Étude Spatiale des Rayonnements, CNRS-UPS, 9 avenue du Colonel Roche, 31028 Toulouse Cedex 4, France
e-mail: suebsuwo@cesr.fr

(Received 6 February 2006 / Accepted 15 March 2006 )

Abstract
Context.We extend the investigation of general relativistic effects on the observed X-ray continuum of Kerr black holes in the context of the light bending model (Miniutti & Fabian 2004).
Aims. Assuming a ring-like illuminating source, co-rotating with the underlying accretion disk, we study the shape and normalisation of the primary and disc reflected continuum as well as the dependence of the observed spectrum on the line of sight for various source heights and radii.
Methods. These calculations are performed using Monte-Carlo methods to compute the angle dependent reflection spectrum from the disc. The effects of general relativity are illustrated by a comparison with Newtonian and Special Relativity calculations.
Results. Relativistic distortions can strongly affect the shape of the reflected spectrum. Light bending can dramatically increase the observable reflected flux and reduce the primary emission. In addition, multiple reflections due to the reflected photons deflected toward the disc can alter significantly the shape of the spectrum above 10 keV. We explore the predicted variations of the observed reflected and primary fluxes with the height and radius of the source. Large variations of the ring radius at constant height can lead to an (unobserved) anti-correlation between primary and reflected flux. In another side, the variability behaviour of several sources can be reproduced if the ring source radius is small (< $5\,r_{\rm g}$ ), and its height varies by a large factor. In particular, a non-linear flux-flux relation, similar to that observed in several sources, can be produced. We compare our model with the flux-flux plot of NGC 4051, and find an agreement for low inclination angles (< $20^\circ$ ), ring source radius $\la$ 3 $r_{\rm g}$ and a height varying between 0.5 to 10 $r_{\rm g}$ . Regarding the angular distribution of the radiation, we find some important qualitative differences with respect to the Newtonian case. The reflected flux at larger inclination is relatively stronger than in the Newtonian model, the reflection fraction increasing with inclination.

Key words: accretion, accretion discs -- black hole physics -- gravitation -- methods: numerical -- relativity -- X-rays: galaxies

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.