Measurement of neutron star parameters: a review of methods for low-mass X-ray binaries

TL;DR

Accurately measuring neutron star parameters like mass, radius, and spin is crucial for understanding their core matter, and this review discusses various methods using low-mass X-ray binaries to reduce uncertainties.

Contribution

This paper reviews multiple observational methods to constrain neutron star parameters, highlighting their combined potential to improve measurement accuracy.

Findings

Multiple methods can be combined to reduce systematic uncertainties.

Each method provides independent constraints on neutron star parameters.

Joint application enhances the accuracy of neutron star measurements.

Abstract

Measurement of at least three independent parameters, for example, mass, radius and spin frequency, of a neutron star is probably the only way to understand the nature of its supranuclear core matter. Such a measurement is extremely difficult because of various systematic uncertainties. The lack of knowledge of several system parameter values gives rise to such systematics. Low-mass X-ray binaries, which contain neutron stars, provide a number of methods to constrain the stellar parameters. Joint application of these methods has a great potential to significantly reduce the systematic uncertainties, and hence to measure three independent neutron star parameters accurately. Here we review the methods based on (1) thermonuclear X-ray bursts; (2) accretion-powered millisecond-period pulsations; (3) kilohertz quasi-periodic oscillations; (4) broad relativistic iron lines; (5) quiescent emissions; and (6) binary orbital motions.