Monte Carlo simulations of radio pulsars and their progenitors

The authors combine models for the evolution of main-sequence stars with an initial mass function and orbital period distribution to simulate the formation of neutron stars. It is assumed that isolated stars in the range of 8 - 20 M_sun; form neutron stars directly in supernovae. Among the effects included in the simulation are (1) mass exchange due to Roche lobe overflow; (2) mass loss from a system in a contact binary stage; (3) changes in a system's orbit caused by mass loss or exchange; (4) the swelling of the secondary as it accretes matter; (5) changes in a system's orbit due to sudden mass ejection in a supernova; and (6) the effect of supernova shell impact on a companion star. It is found that it is difficult to reproduce both the observed velocity distribution of radio pulsars and the observed incidence of binary pulsars. The authors believe it is unlikely that all pulsars are formed in close binary systems and that asymmetries in the supernova explosion, or processes that accelerate a pulsar soon after its birth, are important in determining pulsar velocities.