On the displacement of X-ray binaries from star clusters in star-burst galaxies

TL;DR

This study models the displacement of luminous X-ray binaries from star clusters in star-burst galaxies, revealing significant offsets and correlations that are largely insensitive to cluster properties.

Contribution

It introduces an evolutionary population synthesis model to analyze X-ray binary displacements and their correlation with luminosity in star-burst galaxies.

Findings

Significant spatial offset of X-ray sources from parent clusters.

Correlation between X-ray luminosity and displacement can be roughly reconstructed.

Displacement correlation is insensitive to cluster properties except the common envelope parameter.

Abstract

We have modeled the displacement of luminous X-ray binaries from star clusters in star-burst galaxies with an evolutionary population synthesis code developed by Hurley et al. (2000, 2002). In agreement with Kaaret et al. (2004), we find significant spatial offset of X-ray sources from their parent clusters, and the apparent X-ray luminosity vs. displacement correlation can be roughly reconstructed. The correlation is not sensitive to the fundamental properties of the clusters (e.g., initial mass functions of the binary stars) and the kick velocity imparted to the newborn compact stars, except the common envelope parameter. We present the distributions of the main parameters of the current X-ray binaries, which may be used to constrain the models for the formation and evolution of X-ray binaries with future optical observations.