We numerically investigate the hydrodynamics of accretion disk reversal and relate our findings to the observed spin-rate changes in the accreting X-ray pulsar GX 1+4. In this system, which accretes from a slow wind, the accretion disk contains two dynamically distinct regions. In the inner part viscous forces are dominant and disk evolution occurs on a viscous timescale. In the outer part dyna...

A variety of current models for gamma-ray bursts (GRBs) suggest a common engine a black hole of several solar masses accreting matter from a disk at a rate 0.01 to 10 M ⊙ s. Using a numerical model for relativistic disk accretion, we have studied steady-state accretion at these high rates. Outside about 10 cm, the disk is advection dominated; energy released by dissipation is carried in by the ...

The non-axisymmetric structure of accretion disks around the neutron star in Be/Xray binaries is studied by analyzing the results from three dimensional (3D) Smoothed Particle Hydrodynamics (SPH) simulations. It is found that ram pressure due to the phase-dependent mass transfer from the Be-star disk excites a one-armed, trailing spiral structure in the accretion disk around the neutron star. T...

A self-similar solution for the 3D axi-symmetric radiative MHD equations, which revisits the formation and acceleration of accretion-powered jets in AGNs and microquasars, is presented. The model relies primarily on electromagnetic extraction of rotational energy from the disk plasma and forming a geometrically thin super-Keplerian layer between the disk and the overlying corona. The outflowing...

Using the Hβ linewidth, we obtained the virial central supermassive black hole masses and then the Eddington ratios in a sample of broad-line AGNs and NLS1s observed by ASCA. Combined with the data from ROSAT and Chandra observations, We found a strong correlation between hard/soft X-ray photon index and the Eddington ratio. Such a correlation can be understood by a two-zone accretion flow mode...

We compile the multi-band spectral energy distribution (SED) of Seyfert 1 galaxy NGC4593, and investigate its optical-to-ultraviolet (OUV) continuum and iron Kα line profile. No strong “big blue bump” is found in OUV band. The iron Kα line profile is not as broad as expected from a disk which extends down to the last stable orbit. Both of them can be modeled by a truncated thin disk, and suppor...

We use the microlensing variability observed for nine gravitationally lensed quasars to show that the accretion disk size at 2500Å is related to the black hole mass by log(R2500/cm) = (15.6± 0.2) + (0.54± 0.28) log(MBH/10M⊙). This scaling is consistent with the expectation from thin disk theory (R ∝ M BH), but it implies that black holes radiate with relatively low efficiency, log(η) = −1.29 ± ...

We study semianalytically the gravitational effects on neutrino pair annihilation near the neutrinosphere and around the thin accretion disk. For the disk case, we assume that the accretion disk is isothermal and that the gravitational field is dominated by the Schwarzschild black hole. General relativistic effects are studied only near the rotation axis. The energy deposition rate is enhanced ...

Recent observations show a strong correlation between stellar mass and accretion rate in young stellar and sub-stellar objects, with the scaling Ṁacc ∝ M 2 ∗ holding over more than four orders of magnitude in accretion rate. We explore the consequences of this correlation in the context of disk evolution models. We note that such a correlation is not expected to arise from variations in disk an...

We present the first results from fully general relativistic numerical studies of thick-disk accretion onto a rapidly-rotating (Kerr) black hole with a spin axis that is tilted (not aligned) with the angular momentum vector of the disk. We initialize the problem with the solution for an aligned, constant angular momentum, accreting thick disk around a black hole with spin a/M = J/M = +0.9 (prog...