Thursday, February 9, 2012

1202.1530 (Yucong Zhu et al.)

The Eye of the Storm: Light from the Inner Plunging Region of Black Hole Accretion Discs    [PDF]

Yucong Zhu, Shane W. Davis, Ramesh Narayan, Akshay K. Kulkarni, Robert F. Penna, Jeffrey E. McClintock
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 this plunging region. In this work, 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 this 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.
View original: http://arxiv.org/abs/1202.1530

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