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We discuss the theoretical implications of a study of the periastron passage of the 47 msec pulsar PSR 1259-63 orbiting around a Be star companion. This pulsar is in a very eccentric orbit (e=0.86) with a long orbital period (3.6 years). PSR 1259-63 is expected to interact with the mass outflow from the Be star companion as it approaches periastron (January 9, 1994).
High energy emission (X-rays, hard X-rays and gamma-rays) is expected by shock emission produced by the pulsar relativistic wind termination shock within a `pulsar cavity' perturbing the Be star mass outflow. The high energy emission is time variable as the local magnetic field at the shock and shock radius change as a function of orbital phase. If the Be star mass outflow rate is sufficiently large to quench the pulsar wind and to overcome the centrifugal barrier, accretion may occur near periastron.
PSR 1259-63 is a unique laboratory to study the physics of pulsar shock acceleration in the presence of a large background of soft optical photons with time-variable shock parameters. Several models of relativistic pulsar winds will be discussed with emphasis on the theoretical predictions for the high energy emission. A multiwavength campaign to observe the periastron passage of PSR 1259-63 has been organized. Observations by ASCA, ROSAT, SIGMA and CGRO will sensibly constrain theoretical models of high energy shock emission. We will emphasize the relevance of the PSR 1259-63 system for the understanding of the characteristics of pulsar winds and of the high energy emission from pulsar interacting with gaseous surroundings.
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