Swirling astrophysical flows - efficient amplifiers of Alfven waves

We show that a helical shear flow of a magnetized plasma may serve as an efficient amplifier of Alfven waves. We find that even when the flow is purely ejectional (i.e., when no rotation is present) Alfven waves are amplified through the transient, shear-induced, algebraic amplification process. Series of transient amplifications, taking place sequentially along the flow, may result in a cascade amplification of these waves. However, when a flow is swirling or helical (i.e., some rotation is imposed on the plasma motion), Alfven waves become subject to new, much more powerful shear instabilities. In this case, depending on the type of differential rotation, both usual and parametric instabilities may appear. We claim that these phenomena may lead to the generation of large amplitude Alfven waves and the mechanism may account for the appearance of such waves in the solar atmosphere, in accretion-ejecion flows and in accretion columns. These processes may also serve as an important initial (linear and nonmodal) phase in the ultimate subcritical transition to MHD Alfvenic turbulence in various kinds of astrophysical shear flows.Comment: 12 pages, 11 figures, accepted for publication (25-11-02) in Astronomy and Astrophysic

What can the kinematic complexity of astrophysical shear flows lead to

We develop a method for investigating waves and instabilities in astrophysical shear flows with complex kinematics. Using new tools, we find an unexpected richness in the spectrum of compressible fluctuations sustained by such a flow. The principal characteristic of the revealed exotic phenomena is their asymptotic persistence in the absence of viscosity. "Echoing" as well as strongly unstable (including parametrically driven) solutions are identified. Examples of astrophysical shear flows with nontrivial velocity structure where these method and results can be applied are also discussed

The fourth order of accuracy sequential type rational splitting of inhomogeneous evolution problem

In the present work symmetrized sequential type decomposition scheme of the fourth degree precision for the solution of inhomogeneous evolution problem is constructed. The fourth degree precision is reached by introducing the complex parameter α = 1/2 ± i(1/2√3) and by the approximation of the semigroup through the rational approximation. For the considered scheme the explicit a priori estimation is obtained

Escaping radio emission from pulsars: Possible role of velocity shear

It is demonstrated that the velocity shear, intrinsic to the e{sup +}e{sup {minus}} plasma present in the pulsar magnetosphere, can efficiently convert the nonescaping longitudinal Langmuir waves (produced by some kind of a beam or stream instability) into propagating (escaping) electromagnetic waves. It is suggested that this shear induced transformation may be the basic mechanism needed for the eventual generation of the observed pulsar radio emission

General-relativistic Model of Magnetically Driven Jet

The general scheme for the construction of the general-relativistic model of the magnetically driven jet is suggested. The method is based on the usage of the 3+1 MHD formalism. It is shown that the critical points of the flow and the explicit radial behavior of the physical variables may be derived through the jet ``profile function."Comment: 12 pages, LaTex, no figure

Radio Emission by Particles due to Pulsar Spin

We present a relativistic model for the motion of charged particles in rotating magnetic field lines projected on to a plane perpendicular to the rotation axis. By making an approximation that the projected field lines are straight, an analytical expression is obtained for the particle trajectory. The motive behind developing this model is to elucidate some of the effects of rotation in pulsar profiles. There is a significant contribution to the curvature of particle trajectory due to the rotation of pulsar, which is in addition to the inherent curvature of the field lines. The asymmetry in the observed pulse shapes can be explained by considering the aberration-retardation effects. The single sign circular polarization that has been observed in many pulsars, might be due to the relative orientation of sight line with respect to the particle trajectory plane.Comment: 19 pages, 6 figues. Submitted to Astronomy and Astrophysic

Linear coupling and over-reflection phenomena of magnetohydrodynamic waves in smooth shear flows

Special features of magnetohydrodynamic waves linear dynamics in smooth shear flows are studied. Quantitative asymptotic and numerical analysis are performed for wide range of system parameters when basic flow has constant shear of velocity and uniform magnetic field is parallel to the basic flow. The special features consist of magnetohydrodynamic wave mutual transformation and over-reflection phenomena. The transformation takes place for arbitrary shear rates and involves all magnetohydrodynamic wave modes. While the over-reflection occurs only for slow magnetosonic and Alfv\'en waves at high shear rates. Studied phenomena should be decisive in the elaboration of the self-sustaining model of magnetohydrodynamic turbulence in the shear flows

Dynamics of Charged Particles in the Radio Emission Region of Pulsar Magnetosphere

We consider the classical picture of three dimensional motion of charged particles in pulsar magnetosphere. We adopt a perturbative method to solve the equation of motion, and find the trajectory of particles as they move along the rotating dipolar magnetic field lines. Our aim is to study the influence of rotation on the pulsar radio emission by considering the constrained motion of particles along the open dipolar magnetic field lines. We find that the rotation induces a significant curvature into the particle trajectories. Our model predicts the intensity on leading side dominates over that of trailing side. We expect that if there is any curvature induced radio emission from the region close to the magnetic axis then it must be due to the rotation induced curvature. Our model predicts the radius--to--frequency mapping (RFM) in the core emissions.Comment: 16 pages, 11 figures, Accepted for publication in Astronomy and Astrophysics (2007