Spin‐Kick Correlation in Neutron Stars: Alignment Conditions and Implications

Recent observations of pulsar wind nebulae and radio polarization profilesrevealed a tendency of the alignment between the spin and velocity directionsin neutron stars. We study the condition for spin-kick alignment using a toymodel, in which the kick consists of many off-centered, randomly-orientedthrusts. Both analytical considerations and numerical simulations indicate thatspin-kick alignment cannot be easily achieved if the proto-neutron star doesnot possess some initial angular momentum, contrary to some previous claims. Toobtain the observed spin-kick misalignment angle distribution, the initial spinperiod of the neutron star must be smaller than the kick timescale. Typically,an initial period of a hundred milliseconds or less is required.Comment: 17 pages, 8 figures. Accepted by Ap