Structure of advection-dominated accretion discs with outflows: the role of toroidal magnetic fields

Abstract

The main aim of this paper is studying the effect of toroidal magnetic field on the structure of Advection-Dominated Accretion Flows (ADAF) in the presence of the turbulence viscosity and diffusivity due to viscosity and magnetic field respectively. We use self-similar assumption in radial direction to solve the magnetohydrodynamic (MHD) equations for hot accretion disk. We use spherical coordinate (r, θ, ϕ) to solve our equation. The toroidal component of magnetic field is considered and all three components of the velocity field v ≡ (v r , v θ , v ϕ ) are present in our work. We reduce the equations to a set of differential equations about θ and apply the symmetric boundary condition at the equatorial plane of the disk. Our results indicate that the outflow region, where the redial velocity becomes positive in a certain inclination angle θ 0 , always exist. The results represent that the stronger the magnetic field, the smaller the inclination angle, θ 0 becomes. It means that a magnetized disk is thinner compared to a non-magnetized disk. According to the work by Jiao & Wu 2011, we can define three regions. The first one is called inflow region, which starts from the disk midplane to a certain inclination θ 0 where v r (θ 0 ) = 0. In this region, the velocity has a negative value and the accretion material moves toward the central object. The outflow region, where v r (θ) > 0, is placed between θ 0 and surface of the disk, θ 0 < θ < θ s . In this area, the accretion flow moves away from the central object. The third region, which is located between the surface of the disk and the polar axis, is called wind region. This area is very narrow and the material is blown out from the surface in the form of wind. In this paper we consider two parameters to show the magnetic field effects. These parameters include ratio of gas pressure to magnetic pressure in the equatorial plane of the disk, β 0 , and also magnetic diffusivity parameter, η 0 . Numerical calculations of our model have revealed that the toroidal components of magnetic field has a significant effect on the vertical structure of accretion disk.Many theoretical models have been proposed. One of them is the standard accretion disk model presented by Shakura & Sunyaev 1973. In this model, the disk is assumed to be geometrically thin (H/r ≪ 1), optically thick in the vertical direction and the accreting matter moves with nearly Keplerian velocity. This model explains most of the observational features of X-ray binaries and active galactic nuclei in a highly convincing manner. However, standard disk models cannot reproduce high energy emissions, such as X-ray and gamma rays spectrum. One of the most important processes that is not considered in the standard accretion disk model is advective cooling. In this model, the accret-

The effect of large-scale magnetic field on outflow in ADAFs: an odd symmetry configuration

“…In our previous work, Samadi et al 2014, we investigated the thickness of a hot accretion flow in the presence of the toroidal magnetic field and showed that the disc thickness decreases with increasing the magnetic field strength, and the vertical aspect of the disc is significantly changed in comparison with a nonmagnetic case. Mosallanezhad, Abbassi & Beiranvand (2014), (hereafter MAB14) followed JW11 by adding the toroidal magnetic field. Their results showed that the existence of a magnetic field and its resistivity in a disc can produce more advective energy.…”

Two-dimensional inflow-wind solution of black hole accretion with an evenly symmetric magnetic field

“…In the one-dimensional works, the existence of wind is often an assumption (e.g. Blandford & Begelman 1999;Akizuki & Fukue 2006;Abbassi et al 2008;Zhang & Dai 2008;Bu et al 2009 Mosallanezhad et al 2014;Gu 2015;Samadi & Abbassi 2016 ) but not all (e.g., Narayan & Yi 1995 and references therein). In all these works magnetic field is not included.…”

Self-similar Solution of Hot Accretion Flow with Thermal Conduction and Anisotropic Pressure

“…There are several analytical investigations based on the self-similar assumption that probe the magnetic field effects in hot accretion flows (Akizuki & Fukue 2006;Abbassi et al 2008;Zhang & Dai 2008;Bu et al 2009;Mosallanezhad et al 2014;Samadi et al 2017;Bu & Mosallanezhad 2018;Deng & Bu 2019). In practice, the analytical studies are powerful tools to understand the physical properties of inflow and wind from accretion flow.…”