MHD Theory of Pulsar Winds and Plerions

Young, rapidly rotating pulsars are surrounded by compact synchrotron nebulae, the Crab nebula being the best studied and most known example. These nebulae are continuously pumped by electron-positron plasma and magnetic field emanating from the pulsar in the form of relativistic, magnetized wind. High-resolution images in the X-ray and optical bands revealed a peculiar ``jet-torus'' structure in the inner parts of these nebulae. This discovery clearly indicates significant anisotropy of the pulsar wind, which has been ignored so far in simplified theoretical models of the nebula. The recent radio and IR observations of the Crab suggest, contrary to what has been assumed in the most popular models, that the radio emitting electrons are accelerated now in the same region as the ones responsible for the optical to X-ray emission. All these findings provide important clues about the general physical processes such as self-collimation and energy dissipation in relativistic, magnetized outflows. I discuss physics of pulsar winds and surrounding nebulae focusing attention on attempts to incorporate the new observational results into a self-consistent picture.