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   52064
   We request a total of 120 ks of ASCA time to observe the radio
   pulsar/Be star binary PSR B1259-63 at four orbital phases. Previous
   ASCA detections of the source have demonstrated that this system
   provides the strongest evidence yet that an alternative mechanism to
   accretion, namely shock emission, can produce observable X-ray emission
   in neutron star binaries. Modeling of this system can constrain
   interesting physical parameters, however, only a single orbit has been
   studied to date. We require additional observations to verify that
   previously observed luminosity and spectral variations are not a result
   of time-variable Be star outflow, as well as to test model predictions
   at previously unsampled orbital phases at which the shock emission is
   uncontaminated by radiative cooling.
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