The Velocity Distribution of Isolated Radio Pulsars
Abstract
We infer the velocity distribution of radio pulsars based on largescale 0.4 GHz pulsar surveys. We do so by modeling the evolution of the locations, velocities, spins, and radio luminosities of pulsars, calculating pulsed flux according to a beaming model and random orientation angles of spin and beam, applying selection effects of pulsar surveys, and comparing model distributions of measurable pulsar properties with survey data using a likelihood function. The surveys analyzed have welldefined characteristics and cover ~95% of the sky. We maximize the likelihood in a sixdimensional space of observables P, P, DM, b, μ, and F (period, period derivative, dispersion measure, Galactic latitude, proper motion, and flux density, respectively). The models we test are described by 12 parameters that characterize a population's birth rate, luminosity, shutoff of radio emission, birth locations, and birth velocities. We infer that the radio beam luminosity (1) is comparable to the energy flux of relativistic particles in models for spindriven magnetospheres, signifying that radio emission losses reach nearly 100% for the oldest pulsars, and (2) scales approximately as E^{1/2}, which in magnetosphere models is proportional to the voltage drop available for acceleration of particles. We find that a twocomponent velocity distribution with characteristic velocities of 90 and 500 km s^{1} is greatly preferred to any onecomponent distribution; this preference is largely immune to variations in other population parameters, such as the luminosity or distance scale or the assumed spindown law. We explore some consequences of the preferred birth velocity distribution: (1) roughly 50% of pulsars in the solar neighborhood will escape the Galaxy, while ~15% have velocities greater than 1000 km s^{1} (2) observational bias against highvelocity pulsars is relatively unimportant for surveys that reach high Galactic z distances but is severe for spatially bounded surveys; (3) an important lowvelocity population exists that increases the fraction of neutron stars retained by globular clusters and is consistent with the number of old objects that accrete from the interstellar medium; (4) under standard assumptions for supernova remnant expansion and pulsar spindown, ~10% of pulsars younger than 20 kyr will appear to lie outside of their host remnants. Finally, we comment on the ramifications of our birth velocity distribution for binary survival and the population of inspiraling binary neutron stars relevant to some GRB models and potential sources for LIGO.
 Publication:

The Astrophysical Journal
 Pub Date:
 March 2002
 DOI:
 10.1086/338805
 arXiv:
 arXiv:astroph/0106159
 Bibcode:
 2002ApJ...568..289A
 Keywords:

 Methods: Statistical;
 Stars: Pulsars: General;
 Stars: Neutron;
 Astrophysics
 EPrint:
 16 pages, 4 figures, ApJ (in press). Revisions to reflect refereed version include a new sub(sub)section on effects of the 'standard candle" assumption, and a revised Figure 2. Essential results unchanged