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Origin of the X-ray disc-reflection steep radial emissivity
- Source :
- Astronomy & Astrophysics. 545:A106
- Publication Year :
- 2012
- Publisher :
- EDP Sciences, 2012.
-
Abstract
- X-ray reflection off the accretion disc surrounding a black hole, together with the associated broad iron K$\alpha$ line, has been widely used to constrain the innermost accretion-flow geometry and black hole spin. Some recent measurements have revealed steep reflection emissivity profiles in a number of active galactic nuclei and X-ray binaries. We explore the physically motivated conditions that give rise to the observed steep disc-reflection emissivity profiles. We perform a set of simulations based on the configuration of a possible future high-resolution X-ray mission. Computations are carried out for typical X-ray bright Seyfert-1 galaxies. We find that steep emissivity profiles with $q\sim 4-5$ (where the emissivity is $\epsilon (r) \propto r^{-q}$) are produced considering either i) a lamp-post scenario where a primary compact X-ray source is located close to the black hole, or ii) the radial dependence of the disc ionisation state. We also highlight the role of the reflection angular emissivity: the radial emissivity index $q$ is overestimated when the standard limb-darkening law is used to describe the data. Very steep emissivity profiles with $q \geq 7$ are naturally obtained by applying reflection models that take into account radial profile $\xi (r)$ of the disc ionisation induced by a compact X-ray source located close to the central black hole.<br />Comment: 10 pages, 17 figures, accepted to A\&A
- Subjects :
- High Energy Astrophysical Phenomena (astro-ph.HE)
Physics
Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Active galactic nucleus
Astrophysics::High Energy Astrophysical Phenomena
X-ray
FOS: Physical sciences
Astronomy and Astrophysics
Astrophysics::Cosmology and Extragalactic Astrophysics
Astrophysics
Spectral line
Galaxy
Accretion (astrophysics)
Black hole
Space and Planetary Science
Ionization
Emissivity
Astrophysics::Earth and Planetary Astrophysics
Astrophysics - High Energy Astrophysical Phenomena
Astrophysics::Galaxy Astrophysics
Astrophysics - Cosmology and Nongalactic Astrophysics
Subjects
Details
- ISSN :
- 14320746 and 00046361
- Volume :
- 545
- Database :
- OpenAIRE
- Journal :
- Astronomy & Astrophysics
- Accession number :
- edsair.doi.dedup.....4c7e0bab3814824267ddd803c27003ab