Seeking the nearest neutron stars using a new local electron density map

TL;DR

This paper develops a new local electron density map to improve the distance estimates of nearby pulsars, potentially identifying neutron stars within tens of parsecs for fundamental physics tests.

Contribution

It introduces a local electron density map based on parallax measurements, refining pulsar distance estimates and identifying very-near candidate neutron stars.

Findings

Some pulsars previously estimated at 100-200 pc may be as close as tens of parsecs.

The new map suggests a need for parallax measurements of certain pulsars.

Upcoming telescopes can test neutron star heating mechanisms with these nearby objects.

Abstract

Neutron stars provide a compelling testing ground for gravity, nuclear dynamics, and physics beyond the Standard Model, and so it will be useful to locate the neutron stars nearest to Earth. To that end, we revisit pulsar distance estimates extracted from the dispersion measure of pulsar radio waves scattering on electrons. In particular, we create a new electron density map for the local kiloparsec by fitting to parallax measurements of the nearest pulsars, which complements existing maps that are fit on the Galactic scale. This ``near-Earth'' electron density map implies that pulsars previously estimated to be 100-200 pc away may be as close as tens of parsecs away, which motivates a parallax-based measurement campaign to follow-up on these very-near candidate pulsars. Such nearby neutron stars would be valuable laboratories for testing fundamental physics phenomena, including several late-stage neutron star heating mechanisms, using current and forthcoming telescopes. We illustrate this by estimating the sensitivities of the upcoming Extremely Large Telescope and Thirty Meter Telescope to neutron stars heated by dark matter capture.