Neutron Star Population Dynamics.ii: 3d Space Velocities of Young Pulsars

We use astrometric, distance and spindown data on pulsars to: (1) estimate three-dimensional velocity components, birth distances from the galactic plane, and ages of individual objects; (2) determine the distribution of space velocities and the scale height of pulsar progenitors; (3) test spindown laws for pulsars; (4) test for correlations between space velocities and other pulsar parameters; and (5) place empirical requirements on mechanisms than can produce high velocity neutron stars. Our approach incorporates measurement errors, uncertainties in distances, deceleration in the Galactic potential, and differential galactic rotation. We focus on a sample of proper motion measurements of young pulsars (< 10 Myr) whose trajectories may be accurately and simply modeled. This sample of 47 pulsars excludes millisecond pulsars and other objects that may have undergone accretion-driven spinup. We estimate velocity components and birth z distance on a case-by-case basis assuming the actual age equals the conventional spindown age for a breaking index n=3, no torque decay, and birth periods much shorter than present day periods. Every sample member could have originated within 0.3 kpc of the galactic plane while still having reasonable present day peculiar radial velocities. For the 47-object sample, the scale height of the progenitors is ∼ 0.13 kpc and the three dimensional velocities are distributed in two components with characteristic speeds of 175 −30 km s −1 and 700 −150 km s , representing ∼ 83% and ∼ 17% of the population, respectively. The sample velocities are inconsistent with a single component Gaussian model, well-described by a two component Gaussian model but do not require models of additional complexity. From the best-fit distribution, we estimate that about 20% of the known pulsars will escape the Galaxy, assuming an escape speed of 500 km s. The best-fit, dual-component model, if augmented by an additional, low velocity (< 50 km s) component tolerates, at most, only a small extra contribution in number,