Accretion flows with comparable radiation and gas pressures

Samadi, Maryam; Abbassi, Shahram; Gu, Wei‐Min

doi:10.1093/mnras/stz141

Cited by 6 publications

(4 citation statements)

References 28 publications

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“…To do that, we need to use dynamical models for knowing the essential parameters of a typical accretion flow. Here, we refer to two models; firstly standard discs of Shakura & Sunyev (1973) and secondly accretion flows with comparable radiation and gas pressures (AFCRGP) having finite optical depth introduced by Samadi, Abbassi & Gu (2019). Before going to these models, we specify the common formula of opacity coefficients.…”

Section: Frequency Dependency Of Quantitiesmentioning

confidence: 99%

“…This parameter varies with vertical position and it is specified by βc at the equatorial plane (c index means the value of quantity at the disc's equator). The main difference of this model with standard disc is that two separate energy equations for matter and radiation in the diffusion limit are considered (see Eq.4, 5 of Samadi et al 2019) and the self-similar technique in the radial direction has been employed (for instance density changes as ρ ∝ r −3/2 ). Furthermore, in addition to the radiation cooling, some percentage energy (f adv = Q adv /Qvis) of viscous heating is transported in the radial direction and advected towards the central object.…”

Section: Accretion Flows With Comparable Radiation and Gas Pressuresmentioning

confidence: 99%

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Analytical Solutions of Radiative Transfer Equations in Accretion Discs with Finite Optical Depth

Samadi,

Habibi,

Abbassi

2020

Preprint

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The main purpose of this paper is to obtain analytical solutions for radiative transfer equations related to the vertical structure of accretion discs with finite optical depth. In the non-gray atmosphere, we employ the optical-depth dependent Eddington factor to define the relationship between the mean intensity and radiation stress tensor. Analytical solutions are achieved for two cases: (i) radiative equilibrium, and (ii) a disc with uniform internal heating and both cases are assumed to be in local thermodynamical equilibrium (LTE), too. These solutions enable us to study probable role of scattering and disc optical depth on the emergent intensity and other radiative quantities. Our results show that for the first case, the surface value of mean intensity with constant Eddington factor is three times larger than that with variable factor. Moreover, scattering has no role in the vertical radiative structure of discs with the assumptions of the first case. On the other hand, for the second case, we encounter reductions in all radiative quantities as the photon destruction probability decreases (which is equivalent to increasing scattering). Furthermore, for both cases with total optical depth less than unity, the outward intensity towards the polar direction becomes less than that from the edges of disc which is contrary to limb-darkening. At the end, we apply our results to find the spectrum from accretion systems, based on two dynamical models. Consequently, we can see that how the total optical depth varies with frequency and causes remarkable changes on the emergent spectra.

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Section: Frequency Dependency Of Quantitiesmentioning

confidence: 99%

Section: Accretion Flows With Comparable Radiation and Gas Pressuresmentioning

confidence: 99%

Analytical Solutions of Radiative Transfer Equations in Accretion Discs with Finite Optical Depth

Samadi,

Habibi,

Abbassi

2020

Preprint

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“…While this can be justified in typical ADAFs due to their radiative inefficiency (so that f → 1), it is not as well defined in super-Eddington accretion flows whose radiation is non-negligible. As for other related works in literature, Gu (2012) calculated the vertical structure of radiation pressure-supported accretion disks, and Samadi et al (2019) calculated the vertical structure of accretion disks with comparable gas and radiation pressure, both with detailed calculations of radiation and consequently a variable f, but they both set v θ = 0 so that there is neither outflow nor vertical advection in their solutions. Zahra Zeraatgari et al (2020) presented 2D inflow-outflow solutions of super-Eddington accretion flows with a radial density index n = 1/2 (for ρ ∝ r − n ) and a variable f. The problem is that they applied the symmetric boundary conditions on both the equatorial plane and the polar axis, in which case the integration of the continuity equation along θ direction would yield a net accretion rate of 0 for n ≠ 3/2 (see Jiao 2022, for a detailed derivation).…”

Section: Introductionmentioning

confidence: 99%

Study of Advective Energy Transport in the Inflow and Outflow of Super-Eddington Accretion Flows

Jiao 焦

2023

ApJ

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Photon trapping is believed to be an important mechanism in super-Eddington accretion, which greatly reduces the radiative efficiency as photons are swallowed by the central black hole before they can escape from the accretion flow. This effect is interpreted as the radial advection of energy in one-dimensional height-integrated models, such as the slim-disk model. However, when multidimensional effects are considered, the conventional understanding may no longer hold. In this paper, we study the advective energy transport in super-Eddington accretion based on a new two-dimensional inflow–outflow solution with radial self-similarity, in which the advective factor is calculated self-consistently by incorporating the calculation of radiative flux instead of being set as an input parameter. We found that radial advection is actually a heating mechanism in the inflow due to compression, and the energy balance in the inflow is maintained by cooling via radiation and vertical (θ-direction) advection, which transports entropy upward to be radiated closer to the surface or carried away by the outflow. As a result, fewer photons are advected inward, and more photons are released from the surface, so that the mean advective factor is smaller and the emergent flux is higher than the fluxes predicted by the slim-disk model. The radiative efficiency of super-Eddington accretion thus should be higher than that of the slim-disk model, which agrees with the results of some recent numerical simulations.

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“…While this can be justified in typical ADAFs due to their radiative inefficiency (so that → 1), it is not so well defined in super-Eddington accretion flows whose radiation is non-negligible. As for other related works in literature, Gu (2012) calculated the vertical structure of radiation pressure-supported accretion discs, and Samadi et al (2019) calculated the vertical structure of accretion discs with comparable gas and radiation pressure, both with detailed calculations of radiation and consequently a variable , but they both set = 0 so that there is neither outflow nor vertical advection in their solutions. Zahra Zeraatgari et al (2020) presented twodimensional inflow-outflow solutions of super-Eddington accretion flows with radial density index = 1/2 (for ∝ − ) and a variable .…”

Section: Introductionmentioning

confidence: 99%

Heating or Cooling: Study of Advective Heat Transport in the Inflow and the Outflow of Optically Thin Advection-dominated Accretion Flows

Jiao

2022

ApJ

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Advection is believed to be the dominant cooling mechanism in optically thin advection-dominated accretion flows (ADAFs). When outflow is considered, however, the first impression is that advection should be of opposite sign in the inflow and the outflow, due to the opposite direction of radial motion. Then how is the energy balance achieved simultaneously? We investigate the problem in this paper, analyzing the profiles of different components of advection with self-similar solutions of ADAFs in spherical coordinates (r θ ϕ). We find that for n < 3γ/2 − 1, where n is the density index in ρ ∝ r −n and γ is the heat capacity ratio, the radial advection is a heating mechanism in the inflow and a cooling mechanism in the outflow. It becomes 0 for n = 3γ/2 − 1, and turns to a cooling mechanism in the inflow and a heating mechanism in the outflow for n > 3γ/2 − 1. The energy conservation is only achieved when the latitudinal (θ direction) advection is considered, which takes an appropriate value to maintain energy balance, so that the overall effect of advection, no matter the parameter choices, is always a cooling mechanism that cancels out the viscous heating everywhere. For the extreme case of n = 3/2, latitudinal motion stops, viscous heating is balanced solely by radial advection, and no outflow is developed.

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Accretion flows with comparable radiation and gas pressures

Cited by 6 publications

References 28 publications

Analytical Solutions of Radiative Transfer Equations in Accretion Discs with Finite Optical Depth

Analytical Solutions of Radiative Transfer Equations in Accretion Discs with Finite Optical Depth

Study of Advective Energy Transport in the Inflow and Outflow of Super-Eddington Accretion Flows

Heating or Cooling: Study of Advective Heat Transport in the Inflow and the Outflow of Optically Thin Advection-dominated Accretion Flows

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