A new look at distances and velocities of neutron stars

TL;DR

This paper reevaluates how distances and velocities of neutron stars are determined, emphasizing the importance of priors in distance estimation and proposing a two-Maxwellian model for pulsar velocities based on VLBI data.

Contribution

It demonstrates the necessity of priors in distance calculations and introduces a two-Maxwellian velocity distribution model for young pulsars based on accurate measurements.

Findings

A prior is essential for accurate neutron star distance estimation.

A two-Maxwellian model better fits pulsar velocity data.

Galactic rotation corrections are negligible for velocity calculations.

Abstract

We take a fresh look at the determination of distances and velocities of neutron stars. The conversion of a parallax measurement into a distance, or distance probability distribution, has led to a debate quite similar to the one involving Cepheids, centering on the question whether priors can be used when discussing a single system. With the example of PSRJ0218+4232 we show that a prior is necessary to determine the probability distribution for the distance. The distance of this pulsar implies a gamma-ray luminosity larger than 10% of its spindown luminosity. For velocities the debate is whether a single Maxwellian describes the distribution for young pulsars. By limiting our discussion to accurate (VLBI) measurements we argue that a description with two Maxwellians, with distribution parameters sigma1=77 and sigma2=320 km/s, is significantly better. Corrections for galactic rotation, to derive velocities with respect to the local standards of rest, are insignificant.