Spectral models of convection-dominated accretion flows

Gregory H. Ball; Ramesh Narayan; Eliot Quataert

doi:10.1086/320465

Spectral models of convection-dominated accretion flows

Gregory H. Ball, Ramesh Narayan, Eliot Quataert

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Abstract

For small values of the dimensionless viscosity parameter, namely α ≲ 0.1, the dynamics of non-radiating accretion flows is dominated by convection; convection strongly suppresses the accretion of matter onto the central object and transports a luminosity ∼(10^-3-10^-2)Ṁc² from small to large radii in the flow. A fraction of this convective luminosity is likely to be radiated at large radii via thermal bremsstrahlung emission. We show that this leads to a correlation between the frequency of maximal bremsstrahlung emission and the luminosity of the source, γ_peak ∝ L^2/3. Accreting black holes with X-ray luminosities 10^-4 L_Edd ≳ L_x(0.5-10 keV) ≳ 10^-7 L_Edd are expected to have hard X-ray spectra, with photon indices Γ ∼ 2, and sources with L_x ≲ 10^-9L_Edd are expected to have soft spectra, with Γ ∼ 3.5. This is testable with Chandra and XMM.

Original language	English (US)
Pages (from-to)	221-226
Number of pages	6
Journal	Astrophysical Journal
Volume	552
Issue number	1 PART 1
DOIs	https://doi.org/10.1086/320465
State	Published - May 1 2001
Externally published	Yes

All Science Journal Classification (ASJC) codes

Astronomy and Astrophysics
Space and Planetary Science

Keywords

Accretion, accretion disks
Black hole physics
Convection
X-rays: general

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10.1086/320465

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title = "Spectral models of convection-dominated accretion flows",

abstract = "For small values of the dimensionless viscosity parameter, namely α ≲ 0.1, the dynamics of non-radiating accretion flows is dominated by convection; convection strongly suppresses the accretion of matter onto the central object and transports a luminosity ∼(10-3-10-2)Ṁc2 from small to large radii in the flow. A fraction of this convective luminosity is likely to be radiated at large radii via thermal bremsstrahlung emission. We show that this leads to a correlation between the frequency of maximal bremsstrahlung emission and the luminosity of the source, γpeak ∝ L2/3. Accreting black holes with X-ray luminosities 10-4 LEdd ≳ Lx(0.5-10 keV) ≳ 10-7 LEdd are expected to have hard X-ray spectra, with photon indices Γ ∼ 2, and sources with Lx ≲ 10-9LEdd are expected to have soft spectra, with Γ ∼ 3.5. This is testable with Chandra and XMM.",

keywords = "Accretion, accretion disks, Black hole physics, Convection, X-rays: general",

author = "Ball, {Gregory H.} and Ramesh Narayan and Eliot Quataert",

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doi = "10.1086/320465",

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T1 - Spectral models of convection-dominated accretion flows

AU - Ball, Gregory H.

AU - Narayan, Ramesh

AU - Quataert, Eliot

PY - 2001/5/1

Y1 - 2001/5/1

N2 - For small values of the dimensionless viscosity parameter, namely α ≲ 0.1, the dynamics of non-radiating accretion flows is dominated by convection; convection strongly suppresses the accretion of matter onto the central object and transports a luminosity ∼(10-3-10-2)Ṁc2 from small to large radii in the flow. A fraction of this convective luminosity is likely to be radiated at large radii via thermal bremsstrahlung emission. We show that this leads to a correlation between the frequency of maximal bremsstrahlung emission and the luminosity of the source, γpeak ∝ L2/3. Accreting black holes with X-ray luminosities 10-4 LEdd ≳ Lx(0.5-10 keV) ≳ 10-7 LEdd are expected to have hard X-ray spectra, with photon indices Γ ∼ 2, and sources with Lx ≲ 10-9LEdd are expected to have soft spectra, with Γ ∼ 3.5. This is testable with Chandra and XMM.

AB - For small values of the dimensionless viscosity parameter, namely α ≲ 0.1, the dynamics of non-radiating accretion flows is dominated by convection; convection strongly suppresses the accretion of matter onto the central object and transports a luminosity ∼(10-3-10-2)Ṁc2 from small to large radii in the flow. A fraction of this convective luminosity is likely to be radiated at large radii via thermal bremsstrahlung emission. We show that this leads to a correlation between the frequency of maximal bremsstrahlung emission and the luminosity of the source, γpeak ∝ L2/3. Accreting black holes with X-ray luminosities 10-4 LEdd ≳ Lx(0.5-10 keV) ≳ 10-7 LEdd are expected to have hard X-ray spectra, with photon indices Γ ∼ 2, and sources with Lx ≲ 10-9LEdd are expected to have soft spectra, with Γ ∼ 3.5. This is testable with Chandra and XMM.

KW - Accretion, accretion disks

KW - Black hole physics

KW - Convection

KW - X-rays: general

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VL - 552

SP - 221

EP - 226

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 1 PART 1

ER -

Spectral models of convection-dominated accretion flows

Abstract

All Science Journal Classification (ASJC) codes

Keywords

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