The Effect of Resistivity on the Nonlinear Stage of the Magnetorotational Instability in Accretion Disks

We present three-dimensional magnetohydrodynamic simulations of the nonlinear evolution of the magnetorotational instability (MRI) with a non-zero Ohmic resistivity. The properties of the saturated state depend on the initial magnetic field configuration. In simulations with an initial uniform vertical field, the MRI is able to support angular momentum transport even for large resistivities through the quasi-periodic generation of axisymmetric radial channel solutions rather than through the maintenance of anisotropic turbulence. Simulations with zero net flux show that the angular momentum transport and the amplitude of magnetic energy after saturation are significantly reduced by finite resistivity, even at levels where the linear modes are only slightly affected. This occurs at magnetic Reynolds numbers expected in low, cool states of dwarf novae, these results suggest that finite resistivity may account for the low and high angular momentum transport rates inferred for these systems.Comment: 8 figures, accepted for publication in Ap

Knot in Cen A: Stochastic Magnetic Field for Diffusive Synchrotron Radiation?

The emission of relativistic electrons moving in the random and small-scale magnetic field is presented by diffusive synchrotron radiation (DSR). In this Letter, we revisit the perturbative treatment of DSR. We propose that random and small-scale magnetic field might be generated by the turbulence. As an example, multi-band radiation of the knot in Cen A comes from the electrons with energy $\gamma_e\sim 10^3-10^4$ in the magnetic field of $10^{-3}G$. The multi-band spectrum of DSR is well determined by the feature of stochastic magnetic field. These results put strong constraint to the models of particle acceleration.Comment: accepted by ApJL, comments are welcom