Lutz-Kelker bias in pulsar parallax measurements

TL;DR

This paper analyzes the Lutz-Kelker bias in pulsar parallax measurements, showing that many are significantly overestimated, which impacts astrophysical tests and neutron star property estimates.

Contribution

It extends the Lutz-Kelker bias analysis to neutron stars, incorporating luminosity functions and Galactic models, and assesses the bias in existing measurements.

Findings

Many low-certainty parallax measurements are significantly biased.

The bias affects optical, radio, and dispersion measure-based distance estimates.

Implications for tests of gravity and neutron star radius measurements.

Abstract

Lutz & Kelker showed that parallax measurements are systematically overestimated because they do not properly account for the larger volume of space that is sampled at smaller parallax values. We apply their analysis to neutron stars, incorporating the bias introduced by the intrinsic radio luminosity function and a realistic Galactic population model for neutron stars. We estimate the bias for all published neutron star parallax measurements and find that measurements with less than ~95% certainty, are likely to be significantly biased. Through inspection of historic parallax measurements, we confirm the described effects in optical and radio measurements, as well as in distance estimates based on interstellar dispersion measures. The potential impact on future tests of relativistic gravity through pulsar timing and on X-ray--based estimates of neutron star radii is briefly discussed.