Journal Article

The eye of the storm: light from the inner plunging region of black hole accretion discs

Yucong Zhu, Shane W. Davis, Ramesh Narayan, Akshay K. Kulkarni, Robert F. Penna and Jeffrey E. McClintock

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 424, issue 4, pages 2504-2521
Published in print August 2012 | ISSN: 0035-8711
Published online August 2012 | e-ISSN: 1365-2966 | DOI:
The eye of the storm: light from the inner plunging region of black hole accretion discs

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It is generally thought that the light coming from the inner plunging region of black hole accretion discs contributes negligibly to the disc's overall spectrum, i.e. the plunging fluid is swallowed by the black hole before it has time to radiate. In the standard disc model used to fit X-ray observations of accretion discs, the plunging region is assumed to be perfectly dark. However, numerical simulations that include the full physics of the magnetized flow predict that a small fraction of the disc's total luminosity emanates from the plunging region. We investigate the observational consequences of this neglected inner light. We compute radiative-transfer-based disc spectra that correspond to 3D general relativistic magnetohydrodynamic simulated discs (which produce light inside their plunging regions). In the context of black hole spin estimation, we find that the neglected inner light only has a modest effect (this bias is less than typical observational systematic errors). For rapidly spinning black holes, we find that the combined emission from the plunging region produces a weak power-law tail at high energies. This indicates that infalling matter is the origin for some of the ‘;coronal’ emission observed in the thermal dominant and steep power-law states of X-ray binaries.

Keywords: accretion, accretion discs; black hole physics; MHD; radiative transfer; methods: numerical; X-rays: binaries

Journal Article.  13242 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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