The evolutionary status of PSR 1259−63

The PSR 1259−63 system is unique in that it is the first radio pulsar found to be in a binary system with a massive main sequence companion. As such, it may be the evolutionary missing link connecting the radio pulsars to the x‐ray emitting Be‐binaries. In this paper, we consider the conditions under which PSR 1259−63 may be the progenitor of the less eccentric, more slowly rotating x‐ray Be‐binaries such as 4U0115+63, A0535+26, and A0538−66. Scenarios invoking the interaction of pulsar with the stellar wind of the companion, are proposed to account for the rapid spin down phase which must occur in this system, if it is evolutionarily linked to accreting x‐ray binaries. The unexpected x‐ray emission observed from PSR 1259−63 may indicate that the interaction between the pulsar and the Be star occurs at greater distances and produces a greater spin down efficiency than has been previously calculated.