Uncovering the identities of compact objects in high-mass X-ray binaries and gamma-ray binaries by astrometric measurements

TL;DR

This paper develops a method using precise astrometric measurements to identify the nature of compact objects in high-mass X-ray and gamma-ray binaries, enabling mass estimation and object classification.

Contribution

It introduces a novel approach to determine compact object types in binary systems through astrometric data analysis, improving identification confidence levels.

Findings

Astrometric precision of 70 μas can identify white dwarfs in γ Cas at 99% confidence.

10 μas precision allows high-confidence identification of compact objects in specific binaries.

The method enhances the ability to classify compact objects, such as white dwarfs, neutron stars, or black holes.

Abstract

We develop a method for identifying a compact object in binary systems with astrometric measurements and apply it to some binaries. Compact objects in some high-mass X-ray binaries and gamma-ray binaries are unknown, which is responsible for the fact that emission mechanisms in such systems have not yet confirmed. The accurate estimate of the mass of the compact object allows us to identify the compact object in such systems. Astrometric measurements are expected to enable us to estimate the masses of the compact objects in the binary systems via a determination of a binary orbit. We aim to evaluate the possibility of the identification of the compact objects for some binary systems. We then calculate probabilities that the compact object is correctly identified with astrometric observation (= confidence level) by taking into account a dependence of the orbital shape on orbital parameters and distributions of masses of white dwarfs, neutron stars, and black holes. We find that the astrometric measurements with the precision of 70 $\mu$as for $\gamma$~Cas allows us to identify the compact object at 99% confidence level if the compact object is a white dwarf with 0.6 M$_{\odot}$. In addition, we can identify the compact object with the precision of 10 $\mu$as at 97% or larger confidence level for LS~I~+61$^{\circ}$~303 and 99% or larger for HESS~J0632+057. These results imply that the astrometric measurements with the 10-$\mu$as precision level can realize the identification of compact objects for $\gamma$~Cas, LS~I~+61$^{\circ}$~303, and HESS~J0632+057.