Radiative Spectra from Disk Corona and Inner Hot Flow in Black Hole X-ray Binaries

Abstract

To understand the origin of hard X-ray emissions from black hole X-ray binaries during their low/hard states, we calculate the X-ray spectra of black-hole accretion flow for the following three configurations of hot and cool media: (a) an inner hot flow and a cool outer disk (inner hot flow model), (b) a cool disk sandwiched by disk coronae (disk corona model), and (c) the combination of those two (hybrid model). The basic features we require for successful models are (i) significant hard X-ray emission whose luminosity exceeds that of soft X-rays, (ii) high hard X-ray luminosities in the range of (0.4 - 30) times 10^{37} erg s^{-1}, and (iii) the existence of two power-law components in the hard X-ray band with the photon indices of Gamma_s ~ 2 > Gamma_h, where Gamma_s and Gamma_h are the photon indices of the softer (<10 keV) and the harder (>10 keV) power-law components, respectively. Contribution by non-thermal electrons nor time-dependent evolution are not considered. We find that Models (a) and (b) can be ruled out, since the spectra are always dominated by the soft component, and since only one power-law component, at most, can be reproduced. Only Model (c) can account for sufficiently strong hard X-ray emissions, as well as the existence of the two power-law components, for a large ratio of the accretion rate in the corona to that in the thin disk. The outer disk corona (where the Compton y-parameter is smaller, y < 1) produces the softer power-law component with photon index of Gamma_s ~ 2, whereas the inner hot flow (where y gtrsim 1) generates the harder component with Gamma_h < 2. This model can also account for the observed relationship between the photon index and the reflection fraction.

arXiv comment13 pages, 13 figures, accepted for publication in PASJ

References in corpus (45)

• Advection-Dominated Accretion: A Self-Similar Solution
• Advection-Dominated Accretion: Underfed Black Holes and Neutron Stars
• Modelling the behaviour of accretion flows in X-ray binaries
• Nonthermal Electrons in Radiatively Inefficient Accretion Flow Models of Sagittarius A*
• Thermal Equilibria of Accretion Disks
• Radiation mechanisms and geometry of Cygnus X-1 in the soft state
• The Formation and Structure of a Strongly Magnetized Corona above Weakly Magnetized Accretion Disks
• On the X-ray time lags in the black hole candidates
• Correlation between Compton reflection and X-ray slope in Seyferts and X-ray binaries
• Global Structure and Dynamics of Advection-Dominated Accretion Flows Around Black Holes
• Simultaneous X-ray and gamma-ray observations of Cyg X-1 in the hard state by Ginga and OSSE
• The Soft Gamma-Ray Spectral Variability of Cygnus X-1
• Spectrum of Optically Thin Advection Dominated Accretion Flow around a Black Hole: Application to Sgr A*
• Spectral evolution of magnetic flares and time lags in accreting black hole sources
• Vertical Structure of Gas Pressure-Dominated Accretion Disks with Local Dissipation of Turbulence and Radiative Transport
• ON THE GEOMETRY OF THE X-RAY EMITTING REGION IN SEYFERT GALAXIES
• Magnetic reconnection: flares and coronal heating in Active Galactic Nuclei
• A Magnetohydrodynamic Nonradiative Accretion Flow in Three Dimensions
• Self-Consistent Thermal Accretion Disk Corona Models for Compact Objects: II. Application to Cygnus X-1
• X-ray irradiation in XTE J1817-330 and the inner radius of the truncated disc in the hard state
• Global Three-Dimensional Simulations of Black Hole Accretion Disks: X-ray Flares in the Plunging Region
• Suzaku Results on Cygnus X-1 in the Low/Hard State
• The Existence of Inner Cool Disks in the Low Hard State of Accreting Black Holes
• Two-temperature coronal flow above a thin disk
• The synchrotron boiler and the spectral states of black hole binaries
• An accretion disc-corona model for X-ray spectra of active galactic nuclei
• Formation of Magnetically Supported Disks During Hard-to-Soft Transition in Black Hole Accretion Flows
• Thermal synchrotron radiation and its Comptonization in compact X-ray sources
• On the origin of spectral states in accreting black holes
• Broad-band spectra of Cyg X-1 and correlations between spectral characteristics
• Beyond the standard accretion disc model: coupled magnetic disc--corona solutions with a physically motivated viscosity law
• Spectra from a magnetic reconnection-heated corona in AGN
• Evolution of the 0.01 - 25 Hz power spectral components in Cygnus X-1
• Luminous hot accretion flows: the origin of X-ray emission of Seyfert galaxies and black hole binaries
• Luminous hot accretion flows: thermal equilibrium curve and thermal stability
• Hot accretion discs with thermal Comptonisation and advection in luminous black hole sources
• The Cosmic MeV Gamma-ray Background and Hard X-ray Spectra of Active Galactic Nuclei: Implications for the Origin of Hot AGN Coronae
• Effects of non-thermal tails in Maxwellian electron distributions on synchrotron and Compton processes
• The transition from a cool disk to an ion supported flow
• Low/Hard State Spectra of GRO J1655-40 Observed with Suzaku
• The Dependence of Spectral State Transition and Disk Truncation on Viscosity Parameter $α
• Thermal Equilibria of Magnetically Supported, Black Hole Accretion Disks
• Gamma-rays from Galactic Black Hole Candidates with Stochastic Particle Acceleration
• X-ray Emissions from Three-dimensional Magnetohydrodynamic Coronal Accretion Flows
• Three-dimensional Radiative Properties of Hot Accretion Flows onto the Galactic Centre Black Hole

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• The Emission from Inner Disk and Corona in the Low and Intermediate Spectral States of Black Hole X-ray Binaries
• Effects of adiabatic index on the sonic surface and time variability of low angular momentum accretion flows
• The Spectral Features of Disk and Corona with Mass Evaporation in the Low/Hard State
• Revisiting the structure and spectrum of the magnetic-reconnection-heated corona in luminous AGNs
• Proton Acceleration by Collisionless Shocks in Supermassive Black Hole Coronae: Implications for High-Energy Neutrinos