view Abstract Citations (11) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Two-Temperature Accretion Disks with Winds in a Fluid Approximation Kusunose, Masaaki Abstract The polytropic relation between pressure and density of wind gases is used to obtain solutions for optically thin hot accretion disks with winds. It is assumed that the cooling mechanisms in the disks are bremsstrahlung and Compton scattering. This extends the previous work of Takahara et al. (1989) which did not analyze winds within a self-consistent disk model. It is shown that the disks have winds for accretion rates higher than about 10 percent of the Eddington rate, depending on the viscosity parameter of the disks and the polytropic exponent of wind gases. The poloidal velocity of winds at the foot-point is shown to be as high as 10 percent of light speed. Publication: The Astrophysical Journal Pub Date: April 1991 DOI: 10.1086/169837 Bibcode: 1991ApJ...370..505K Keywords: Accretion Disks; Black Holes (Astronomy); Galactic Nuclei; Magnetohydrodynamics; Plasma Temperature; Bremsstrahlung; Compton Effect; Numerical Analysis; Optical Thickness; Radial Distribution; Astrophysics; ACCRETION; BLACK HOLES; GALAXIES: NUCLEI; HYDRODYNAMICS full text sources ADS |
We examine the applicability of the stochastic electron acceleration to two high synchrotron peaked blazars, Mrk 421 and Mrk 501, assuming synchrotron self-Compton emission of gamma-rays. Our model considers an emitting region moving at relativistic speed, where non-thermal electrons are accelerated and attain a steady-state energy spectrum together with the photons they emit. The kinetic equations of the electrons and photons are solved numerically, given a stationary wavenumber spectrum of the magnetohydrodynamic (MHD) disturbances, which are responsible for the electron acceleration and escape. Our simple formulation appears to reproduce the two well-sampled, long-term averaged photon spectra. In order to fit the model to the emission component from the radio to the X-ray bands, we need both a steeper wave spectral index than the Kolmogorov spectrum and efficient particle escape. Although the model provides a natural explanation for the high-energy cutoff of the electron energy distribution, the derived physical parameters raise a problem with an energy budget if the MHD waves with the Alfvén velocity are assumed to be the acceleration agent.
The effects of external heating on the stability of hot accretion disks are studied in some detail. It is known that geometrically thin, optically thick, nonirradiated accretion disks have two distinct branches in the surface density mass-accretion rate plane: the upper branch is radiation pressure-dominated and is unstable against thermal and secular perturbations, while the lower one is gas-pressure-dominated and is stable. We show quite generally that, even when disks are strongly irradiated, the upper branch remains unstable and the lower branch remains stable; the lower branch, however, can become radiation pressure dominated, if the irradiating flux, F(irr), is kept constant. A stable, radiation pressure dominated state thus appears. If F(irr) changes in proportion to the mass-accretion rate through the disk, the instabilities associated with radiation pressure dominated disks cannot be removed. Some observational implications are discussed in the context of long-term variations of low-mass X-ray binaries.
The optically thin, advection-dominated accretion flows are thermally stable against global perturbations. In addition, they have high temperatures because of inefficient radiative cooling. They are thus promising candidates of models to explain the high energy emission of X-ray stars and AGNs. So far, models, however, take no account of the advective heat transport in determining the thermal structure of the electron system. The validly of this neglect, however, must be checked by integrating the electron energy equation globally as well as the ion energy one.
We show all the thermal equilibrium solutions for given α and black hole mass in the (surface density, accretion rate)-plane and the (surface density, temperature)-plane. Solutions show transitions from optically thick disks to thin disks, one-temperature to two-temperature, and e+e- pair-free disks to pair-dominated disks
