LOCAL-DISTRIBUTION OF OLD NEUTRON-STARS

The local distribution of old disk neutron stars is approximately with a one-dimensional model, in which the steady state distribution in the direction perpendicular to the Galactic plane is calculated, assuming a variety of the initial radio pulsar positions and velocities, and various Galactic potentials. We find that the local distribution of old neutron stars is dominated by those that were born with very low velocities. The high-velocity neutron stars spend most of their lifetime far in the Galactic halo and do not contribute much to the local density. Therefore, the r.m.s. velocity at birth is not a good indicator of the scale height of the old population. The most likely half-density scale height for the old disk neutron stars is approximately 350 pc, the same as for the old disk G, K, and M stars. If gamma-ray bursts originate on old disk neutron stars, then 350 pc should also be the scale height for the bursters.