PERIOD EVOLUTION OF PSR B1259-63 - EVIDENCE FOR PROPELLER-TORQUE SPINDOWN

PSR B1259-63 has a pulse period of 47.7 ms and is in a highly eccentric 3.5 yr orbit around the Be star SS 2883. Timing observations of this pulsar, made over a 4.8 yr interval using the Parkes radio telescope, cover two periastron passages, in 1990 August, and 1994 January. The timing data cannot be fitted by the normal pulsar and Keplerian binary parameters but are well fitted by a model which includes pulsar spin-down episodes at each periastron. The most likely explanation is that the pulsar is interacting with the circumstellar disk of SS 2883 via the propeller mechanism.