Pulsar spin-velocity alignment from single and binary neutron star progenitors

Abstract

ABSTRACT The role of binary progenitors of neutron stars (NSs) in the apparent distribution of space velocities and spin-velocity alignment observed in young pulsars is studied. We performed a Monte Carlo synthesis of pulsar populations originated from single and binary stars with different assumptions about the NS natal kick (kick-spin alignment, kick amplitude and kick reduction in electron-capture supernovae in binary progenitors with initial main-sequence masses from the range 8-11 M⊙ which experienced mass exchange due to Roche lobe overflow). The calculated spin-velocity alignment in pulsars is compared with data inferred from radio polarization measurements. The observed space velocity of pulsars is found to be mostly affected by the natal kick velocity form and its amplitude; the fraction of binaries is not important here for reasonably large kicks. The natal kick-spin alignment is found to strongly affect the spin-velocity correlation of pulsars. Comparison with the observed pulsar spin-velocity angles favours a sizeable fraction of binary progenitors and kick-spin angles ∼5°-20°. © 2009 RAS.