Abstract
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.
Highlights
The ubiquity and simplicity of black holes (BHs) in our Universe make them truly marvellous objects of study
The only available probe is the accretion disc orbiting the BH, which transitions from nearly circular orbits to plunging at a special location known as the innermost stable circular orbit (ISCO)
The harder overall spectrum of general relativistic magnetohydrodynamic (GRMHD) compared to NT implies that there would be an asymmetric error in BH spin estimates
Summary
The ubiquity and simplicity of black holes (BHs) in our Universe make them truly marvellous objects of study. The game of measuring BH masses has been played as early as 1972 for Cygnus X-1 (Bolton 1972; Webster & Murdin 1972), and to date we have robust mass estimates for about 20 stellar mass binary BH systems (Remillard & McClintock 2006; Orosz et al 2007, 2009, 2011a,b; Cantrell et al 2010), and 64 supermassive BHs (Gultekin et al 2009; Graham et al 2011). Despite this success in measuring BH mass, spin has been a more difficult quantity to obtain. A measurement of the ISCO size yields the BH spin if the mass is independently known
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have