Modelling steep radial emissivity in relativistic iron lines from black-hole accretion discs
Abstract
X-ray spectroscopy of active galaxies and black hole binaries provides an opportunity to explore the innermost regions of black hole accretion discs. Some of the recent measurements have revealed a very steep radial decrease of the disc reflection emissivity, especially in the central region, suggesting the disc-irradiating corona to be compact and very centrally localised. We discuss whether the special conditions on the corona properties are indeed required, and / or whether the steep radial emissivity could be an artefact of model assumptions. The inter-dependencies and possible degeneracies between the radial emissivity index and other parameters of the relativistic reflection model are studied. A set of simulations using a preliminary response matrix for a planned Athena mission is performed for this purpose. We show that the measurements of the radial emissivity are indeed degenerate with some model assumptions and parameters, even for more sensitive spectra than for those available from current X-ray missions. We also realise that the radial dependence of the disc ionisation might be another factor which can account for the steep radial emissivities.
- Publication:
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Proceedings of RAGtime 10-13
- Pub Date:
- December 2014
- Bibcode:
- 2014bhns.work..209S
- Keywords:
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- black holes;
- accretion discs;
- relativistic iron lines