Analytic Model for Advection‐dominated Accretion Flows in a Global Magnetic Field

Kaburaki, Osamu

doi:10.1086/308442

Cited by 34 publications

(46 citation statements)

References 17 publications

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“…In other words, the accretion flow of our model is not infinitely conducting. For simplicity, we could assume the resistivity to be constant (see, e.g., Kaburaki 2000). However, we assume that the magnetic diffusivity is due to turbulence in the accretion flow and it is reasonable to express this parameter in analogy to the α-prescription of Shakura & Sunyaev (1973) for the turbulent viscosity,…”

Section: Formulation Of the Problemmentioning

confidence: 99%

A model for quasi-spherical magnetized accretion flow

Shadmehri¹

2004

A&A

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Abstract.A model for axisymmetric magnetized accretion flow is proposed. The dominant mechanism of energy dissipation is assumed to be the magnetic diffusivity due to turbulence in the accretion flow. In analogy to the advection-dominated accretion flow (ADAF) solutions, a constant fraction of the resistively dissipated energy is stored in the accreting gas and the rest is radiated. We first introduce the general self-similar solutions which describe a resistive and nonrotating flow with purely poloidal magnetic field. The radial dependence of physical quantities is identical to that in viscous ADAF solutions. Although the main focus of this study is on nonrotating magnetized accretion flow, for rotating flow with both poloidal and toroidal components of magnetic field we find a radial scaling of solutions similar to the nonrotating case. We show that the accretion and the rotation velocities are both below the Keplerian rate, irrespective of the amount of cooling. We show that the set of equations is reduced to one second order differential equation for a nonrotating flow. The geometrical shape of the disk changes depending on the fraction of the resistively dissipated energy which is stored in the accreting gas. However, there is a hot low-density gas above the disk in almost all cases. The net accretion rate is calculated for a set of illustrative parameters.

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Section: Formulation Of the Problemmentioning

confidence: 99%

A model for quasi-spherical magnetized accretion flow

Shadmehri¹

2004

A&A

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“…However, recent works represent importance of magnetic diffusivity in accretion discs (e.g. Kuwabara et al 2000;Kaburaki 2000 ;Kaburaki et al 2002;Sh04;Ghanbari et al 2007;Krasnopolsky et al 2010;Kaburaki et al 2010). Sh04 studied a quasi-spherical accretion flow that dominant mechanism of energy dissipation was assumed to be the magnetic diffusivity due to turbulence in the accretion flow and the viscosity of the fluid was completely neglected.…”

Section: Introductionmentioning

confidence: 99%

Self-Similar Solutions for Viscous and Resistive Advection Dominated Accretion Flows

Faghei

2012

J Astrophys Astron

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Abstract.In this paper, the self-similar solution of resistive advection dominated accretion flows (ADAF) in the presence of a pure azimuthal magnetic field is investigated. The mechanism of energy dissipation is assumed to be the viscosity and the magnetic diffusivity due to turbulence in the accretion flow. It is assumed that the magnetic diffusivity and the kinematic viscosity are not constant and vary by position and α-prescription is used for them. In order to solve the integrated equations that govern the behavior of the accretion flow, a self-similar method is used. The solutions show that the structure of accretion flow depends on the magnetic field and the magnetic diffusivity. As, the radial infall velocity and the temperature of the flow increase, and the rotational velocity decreases. Also, the rotational velocity for all selected values of magnetic diffusivity and magnetic field is sub-Keplerian. The solutions show that there is a certain amount of magnetic field that the rotational velocity of the flow becomes zero. This amount of the magnetic field depends on the gas properties of the disc, such as adiabatic index and viscosity, magnetic diffusivity, and advection parameters. The solutions show the mass accretion rate increases by adding the magnetic diffusivity and in high magnetic pressure case, the ratio of the mass accretion rate to the Bondi accretion rate decreases as magnetic field increases. Also, the study of Lundquist and magnetic Reynolds numbers based on resistivity indicates that the linear growth of magnetorotational instability (MRI) of the flow decreases by resistivity. This property is qualitatively consistent with resistive magnetohydrodynamics (MHD) simulations.

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“…The effects of a magnetic field on the disc were also studied (see Balbus & Hawley 1998; Kaburaki 2000; Shadmehri 2004; Meier 2005; Shadmehri & Khajenabi 2005, hereafter SK0; Akizuki & Fukue 2006; Shadmehri & Khajenabi 2006, hereafter SK06; Ghanbari, Salehi & Abbassi 2007). Balbus & Hawley (1998) discussed the MHD turbulence initiated by magnetorotational instability (MRI) and its effects on the angular momentum transportation.…”

Section: Introductionmentioning

confidence: 99%

Self-similar structure of magnetized advection-dominated accretion flows and convection-dominated accretion flows

Zhang

Dai

2008

Monthly Notices of the Royal Astronomical Society

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We study the effects of a global magnetic field on viscously rotating and vertically integrated accretion discs around compact objects using a self‐similar treatment. We extend Akizuki & Fukue's work by discussing a general magnetic field with three components (r, ϕ, z) in advection‐dominated accretion flows (ADAFs). We also investigate the effects of a global magnetic field on flows with convection. For these purposes, we first adopt a simple form of the kinematic viscosity ν=αc2s/ΩK to study magnetized ADAFs: a vertical and a strong magnetic field, for instance, not only prevents the disc from being accreted but also decreases the isothermal sound speed. Then, we consider a more realistic model of the kinematic viscosity ν=αcsH, which makes the infall velocity increase but the sound speed and toroidal velocity decrease. We next use two methods to study magnetized flows with convection, i.e. we take the convective coefficient αc as a free parameter to discuss the effects of convection for simplicity. We establish the αc–α relation for magnetized flows using the mixing‐length theory and compare this relation with the non‐magnetized case. If αc is set as a free parameter, then |vr| and cs increase for a large toroidal magnetic field, while |vr| decreases but |vϕ| increases (or decreases) for a strong and dominated radial (or vertical) magnetic field with increasing αc. In addition, the magnetic field makes the αc–α relation be distinct from that of non‐magnetized flows, and allows the ρ∝r−1 or ρ∝r−2 structure for magnetized non‐accreting convection‐dominated accretion flows with α+gαc < 0 (where g is the parameter to determine the condition of convective angular momentum transport).

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Analytic Model for Advection‐dominated Accretion Flows in a Global Magnetic Field

Cited by 34 publications

References 17 publications

A model for quasi-spherical magnetized accretion flow

A model for quasi-spherical magnetized accretion flow

Self-Similar Solutions for Viscous and Resistive Advection Dominated Accretion Flows

Self-similar structure of magnetized advection-dominated accretion flows and convection-dominated accretion flows

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