ENERGY-TRANSPORT IN A ROTATION-MODULATED PULSAR WIND

A rotation-powered pulsar generates large-amplitude, oscillating elect romagnetic fields in its relativistic wind. The importance of these fi elds in transporting energy within the wind and determining the struct ure of the wind is investigated here. It is shown that the theory of i deal magnetohydrodynamics (MHD) underpinning standard, steady-state wi nd models does not apply throughout the wind and must be replaced by a n exact one-fluid theory that includes a generalized, relativistic Ohm 's law. It is also shown, by constructing the wind artificially from t he pulsar's vacuum fields by adding test particles, that the wind disp lacement current asymptotically dominates the conduction current; that Poynting flux is asymptotically transported by large-amplitude, trans verse electromagnetic waves which strongly accelerate particles (i.e., an outer radiation zone); that the inner boundary of the radiation zo ne lies well inside the wind termination shock for the Crab pulsar; an d that at lesser distances, where transverse waves are catastrophicall y damped, the wind displacement current is associated with longitudina l oscillating fields. A self-consistent fluid model of the radiation z one predicts that the kinetic energy flux dominates the Poynting flux if the Lorentz factor of the flow is large and there is no local heati ng. Thus the existence of a radiation zone partially explains a featur e of the Crab pulsar wind that has hitherto seemed paradoxical in the context of standard wind models - namely, that the flow is Poynting-fl ux-dominated at the light cylinder by virtue of its generation in pair cascades, yet needs to be kinetic-flux-dominated at the termination s hock if pressure confinement of the Crab nebula by its supernova remna nt is to be self-consistently achieved. However, a complete resolution of the paradox must await the identification of a plausible flux conv ersion process, an issue that this paper does not address.