The singular differential equations for finite temperature relativistic magnetohydrodynamic (MHD) winds integrate to two algebraic equations when the source magnetic field is a monopole. This simplification enables an extensive characterization of the asymptotic wind solutions in terms of source parameters. We will consider only the critical solutions-those that pass smoothly through both an intermediate (Alfvenic) and a fast MHD critical point and expand to zero pressure at infinite radial distance from the source. Because the constants of motion must be specified to extremely high accuracy, the critical solutions cannot be found analytically. Synopsis of many numerical solutions reveals a uniform parametric characterization of the asymptotic wind in terms of one combination of source parameters, Z, the mean source particle energy divided by mc2u1 '. where u is a generalization of Michel's (1969) cold relativistic wind strength parameter. Cool winds, with Z < I, behave asymptotically much as Michel's cold wind minimum torque solution; Z > 1 hot winds have quite different, but simply characterized, asymptotic solutions. Thus, the strength of magnetized relativistic outflows can depend critically upon the temperature of the source.

The structure of both the interior and exterior pulsar magnetosphere depends upon the strength of its plasma source near the surface of the star. We review magnetospheric models in the light of a vacuum pair-production source model proposed by Sturrock, and Ruderman and Sutherland. This model predicts the existence of a cutoff, determined by the neutron star's spin rate and magnetic field strength, beyond which coherent radio emission is no longer possible. The observed distribution of pulsar spin periods and period derivatives, and the distribution of pulsars with missing radio pulses, is quantitatively consistent with the pair production threshold, when its variation of neutron star radius and moment of inertia with mass is taken into account. All neutron stars observed as pulsars can have relativistic magnetohydrodynamic wind exterior magnetospheres. The properties of the wind can be directly related to those of the pair production source. Radio pulsars cannot have relativistic plasma wave exterior magnetospheres. On the other hand, most erstwhile pulsars in the galaxy are probably halo objects that emit weak fluxes of energetic photons that can have relativistic wave exterior magnetospheres. Extinct pulsars have not been yet observed. * Proceedings of the NASA/JPL Workshop on the Physics of Planetary and Astrophysical Magnetospheres.

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We review efforts to construct a self-consistent model of pulsar magnetospheres that links the particle source near the pulsar to the outflowing relativistic wind and couples the wind to the surrounding nebula. Pair production source models (Sturrock, 1971; Ruderman and Sutherland, 1975; Arons, 1979) produce outflowing positronic plasmas which are too dense to support a plasma wave of relativistic amplitude (Kennel et al., 1973). Therefore an appropriate description seems to be a relativistic magnetohydrodynamic (MHD) wind. Radiation from a relativistic wind will be collimated forward and can only be observed along the line of sight to the wind source. This makes relativistic winds essentially unobservable and provides an almost invisible method of energy transport. Photons can be emitted in all directions and the existence of the wind inferred only after the wind has been decelerated by a confining shock (causing the flow to become subsonic and non-relativistic).