Hunting isolated neutron stars with proper motions from wide-area optical surveys

TL;DR

This paper assesses the potential of wide-area optical surveys, like LSST, to detect high-velocity isolated neutron stars by modeling their luminosity evolution, proper motions, and thermal properties, offering insights into neutron star physics.

Contribution

It introduces a model predicting the number and properties of detectable HVNSs in upcoming optical surveys, including effects of dark matter heating on neutron star temperatures.

Findings

Approximately 10 HVNSs detectable with LSST over 10 years.

Detection of neutron stars cooler than current X-ray survey limits.

Dark matter heating could make HVNSs significantly cooler and more detectable in optical.

Abstract

High-velocity neutron stars (HVNSs) that were kicked out from their birth location can be potentially identified with their large proper motions, and possibly with large parallax, when they come across the solar neighborhood. In this paper, we study the feasibility of hunting isolated HVNSs in wide-area optical surveys by modeling the evolution of NS luminosity taking into account spin-down and thermal radiation. Assuming the upcoming 10-year VRO LSST observation, our model calculations predict that about 10 HVNSs mainly consisting of pulsars with ages of $10^4$--$10^5$ yr and thermally emitting NSs with $10^5$--$10^6$ yr are detectable. We find that a few NSs with effective temperature $< 5 \times 10^5$ K, which are likely missed in the current and future X-ray surveys, are also detectable. In addition to the standard neutron star cooling models, we consider a dark matter heating model. If such a strong heating exists we find that the detectable HVNSs would be significantly cooler, i.e., $\lesssim 5\times 10^5$ K. Thus, the future optical observation will give an unique NS sample, which can provide essential constraints on the NS cooling and heating mechanisms. Moreover, we suggest that providing HVNS samples with optical surveys is helpful for understanding the intrinsic kick-velocity distribution of NSs.