Observational Constraints on Pulsar Wind Theories

Two-dimensional, relativistic, MHD simulations of pulsar-wind powered nebulae provide strong constraints on the properties of the winds themselves. In particular, they confirm that Poynting flux must be converted into particle energy close to or inside the termination shock front, emphasising the puzzle known as the $\sigma$ paradox. To distinguish between the different possible resolutions of this paradox, additional observational constraints are required. In this paper, I briefly discuss two recents developments in this respect: the modelling of high time-resolution optical polarimetry of the Crab pulsar, and the detection of the pulsar/Be star binary PSR 1259-63 in TeV energy gamma-rays.