The shock termination of a relativistic magnetohydrodynamic wind from a pulsar is the most interesting and viable model for the excitation of the synchrotron sources observed in pulsar driven (‘‘plerionic’’) supernova remnants. I describe results on the structure of relativistic magnetosonic shock waves in plasmas composed of electrons and positrons plus heavy ions as a minority constituent by number. Relativistic shocks in symmetric pair plasmas create fully thermalized distributions of particles and fields downstream. Therefore, such shocks are not good candidates for the mechanism which converts rotational energy lost from a pulsar into the nonthermal synchrotron emission observed in plerions. However, when the upstream wind contains heavy ions which are a minority constituent by number density, but carry the bulk of the energy density, much of the energy of the shock goes into a downstream, nonthermal power law distribution of pairs with energy distribution N(E)dEEs. In a specific model presented in some detail, s=1.7, with approximately 20% efficiency in converting upstream flow energy into downstream energy in nonthermally accelerated particles. These characteristics are close to those assumed for the pairs in macroscopic MHD wind models of plerion excitation. The acceleration mechanism is collective synchrotron emission of elliptically polarized extraordinary modes by the ions in the shock front at high harmonics of the ion cyclotron frequency, with the downstream pairs absorbing almost all of this radiation, mostly at their fundamental (relativistic) cyclotron frequencies.

The spatial structure of the shock includes compressional overshoots of the magnetic field strength above what would be expected from the MHD jump conditions, at places where the ions are reflected. I outline a new model of the inner regions of the Crab Nebula, in which I propose that the shock structure is angularly resolved and the optical ‘‘wisps’’ are surface brightness enhancements created in the compressional overshoots of the magnetic field within and just down stream from the shock. I also briefly outline the application of these results to the relativistic shocks believed to terminate the winds from pulsars in compact binaries.

This content is only available via PDF.
You do not currently have access to this content.