Trans-fast MHD winds in a pulsar magnetosphere

Abstract

We consider the problem of how a pulsar wind dominated by electro-magnetic energy converts itself into a kinetic energy-dominated wind, that is required by magnetohydrodynamical (MHD) models of interaction between the pulsar and the nebula. It is known that stationary, ideal-MHD wind models based on radial configurations are incapable of explaining the energy conversion from the electro-magnetic energy to the plasma's kinetic energy. For non-radial field geometries, we consider a detailed analysis of the critical conditions of trans-fast MHD winds and discuss the effects of the magnetic field on the wind acceleration. Although the flow properties associate with the magnetic flux tube divergence, we survey the acceptable ranges of the wind parameters as a pulsar wind. Further, we demonstrate the Crab pulsar wind with a magnetic flux tube diverging as ∝ x-0.4. We see that the rapid acceleration is caused by a nearby Alfvén point; the velocity is almost terminated within several thouthand times of the fast magnetosonic point; thus, the kinetic energy-dominated wind is realized.