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X-ray emission has been detected from the radio pulsar PSR1259-63 during two pointed ROSAT observations, taken six months apart. This 47.7 msec radio pulsar is apparently in a highly eccentric ($\epsilon >$ .95) binary system with the 15 $M_{\sun}$ Be-star SS2883. It is the first radio pulsar found to be in a binary system with a massive main sequence companion; it is also the most highly eccentric binary system known to contain a neutron star. The level of X-ray flux detected in the ROSAT observations is more than 1000 times greater than what would be expected from the Be-star companion's coronal emission. Several theoretical models, such as rotational spin down energy losses, low-level accretion, or emission from a shocked stellar wind, have been proposed to explain this level of flux. These models are explored to see if they are consistent with the observations, and the results of our search for the 47.7 ms pulsations will be presented.
