On the escape of low-frequency waves from magnetospheres of neutron stars

We study the nonlinear decay of the fast magnetosonic into the Alfv\'en waves in relativistic force-free magnetohydrodynamics. The work has been motivated by models of pulsar radio emission and fast radio bursts (FRBs), in which the emission is generated in neutron star magnetospheres at conditions when not only the Larmor but also the plasma frequencies significantly exceed the radiation frequency. The decay process places limits on the source luminosity in these models. We estimated the decay rate and showed that the phase volume of Alfv\'en waves available for the decay of an fms wave is infinite. Therefore the energy of fms waves could be completely transferred to the small-scale Alfv\'en waves not via a cascade, as in the Kolmogorov turbulence, but directly. Our results explain the anomalously low radio efficiency of the Crab pulsar and show that FRBs could not be produced well within magnetar magnetospheres.Comment: ApJ, in pres

On the Escape of Low-frequency Waves from Magnetospheres of Neutron Stars

We study the nonlinear decay of the fast magnetosonic (fms) into the Alfvén waves in relativistic force-free magnetohydrodynamics. The work has been motivated by models of pulsar radio emission and fast radio bursts (FRBs), in which the emission is generated in neutron star magnetospheres at conditions when not only the Larmor but also the plasma frequencies significantly exceed the radiation frequency. The decay process places limits on the source luminosity in these models. We estimated the decay rate and showed that the phase volume of Alfvén waves available for the decay of an fms wave is infinite. Therefore, the energy of fms waves could be completely transferred to the small-scale Alfvén waves not via a cascade, as in the Kolmogorov turbulence, but directly. Our results explain the anomalously low radio efficiency of the Crab pulsar and show that FRBs could not be produced well within magnetar magnetospheres

On helical behavior of turbulence in the ship wake

Turbulent ship wake conservation at a long distance is among unsolved problems at present. It is well known that far wakes have a vortical structure and slowly expand with distance. As was obtained by Dubrovin et al., slow expansion of the wake may be related to the distribution of turbulent viscosity in it. In our work we study the effect of helicity in the wake on the behavior of turbulent viscosity. Taking into account the helical nature of the wake, we can clarify the difference between turbulence inside and outside the wake on the one hand and slowing down of its expansion with time on the other hand. © 2013 Publishing House for Journal of Hydrodynamics

Turbulent Viscosity Variability in Self-Preserving Far Wake with Zero Net Momentum

The profile of the self-preserving far wake with zero net momentum depends on the effective turbulent viscosity coefficient. The current model is based on the assumption of uniform viscosity in the wake cross section. It predicts the self-similar shape of the wake where the width W depends on the distance z from the body as W∝z1/5 for the axisymmetric case (or z1/4 for the plane case). The observed wake width, however, demonstrates the dependence W∝zα (where α⩽1/5). We generalize the model of a self-preserving far wake for the case of the turbulent viscosity coefficient depending on the radius. Additional integrals of motion allow a new family of self-similar profiles with α⩽1/5

Theory Helps Observations : Determination of the Shock Mach Number and Scales From Magnetic Measurements

The Mach number is one of the key parameters of collisionless shocks. Understanding shock physics requires knowledge of the spatial scales in the shock transition layer. The standard methods of determining the Mach number and the spatial scales require simultaneous measurements of the magnetic field and the particle density, velocity, and temperature. While magnetic field measurements are usually of high quality and resolution, particle measurements are often either unavailable or not properly adjusted to the plasma conditions. We show that theoretical arguments can be used to overcome the limitations of observations and determine the Mach number and spatial scales of the low-Mach number shock when only magnetic field data are available