HIGH-ENERGY EMISSION FROM THE ECLIPSING MILLISECOND PULSAR PSR 1957+20

We study the properties of the high-energy emission expected from the eclipsing millisecond pulsar system PSR 1957+20. We consider emission by both the relativistic shock produced by the pulsar wind in the nebula surrounding the binary and by the shock constraining the mass outflow from the companion star of PSR 1957+20. We use the results of microscopic plasma physical models of relativistic shocks to suggest that the high-energy radiation is produced in the range from X-rays to approximately MeV gamma-rays in the binary and in the range from approximately 10(-2) eV to approximately 40 keV in the nebula. The source is expected to be too weak for detection by the instruments on board the Compton Gamma-Ray Observatory (GRO) in their normal pointing mode. However, ROSAT may be able to observe the high-energy emission from within the binary. If the parameters of the pulsar wind (ratio of kinetic energy flux to Poynting flux, ratio of heavy ion flow energy density to flow energy density of pairs, fraction of open field line voltage expended in accelerating ions) are similar to the values inferred by applying similar models to the Crab Nebula, ROSAT should be able to detect the emission from within the binary at the level of approximately 10(-3) photons s-1. Doppler boost of the emission in the radiating wind suggests the flux should vary on the orbital time scale, with the largest flux observed roughly coincident with the pulsar's radio eclipse. Thus ROSAT observations and possibly a dedicated long GRO observation of PSR 1957+20 can be used to gain information about the physics of pulsar winds interacting with their close environments.