Observational evidence for the origin of X-ray sources in globular clusters

TL;DR

This paper investigates the origins of various X-ray sources in globular clusters, emphasizing the roles of stellar encounters and primordial binaries, and introduces a new statistical method for analysis.

Contribution

It presents a novel statistical approach to distinguish the formation mechanisms of X-ray sources in globular clusters, highlighting the importance of cluster mass and primordial binaries.

Findings

Cluster mass is not a reliable proxy for stellar encounter rate.

Optical identifications are crucial for confirming primordial binaries.

Some active binaries are brighter than previously expected.

Abstract

Low-mass X-ray binaries, recycled pulsars, cataclysmic variables and magnetically active binaries are observed as X-ray sources in globular clusters. We discuss the classification of these systems, and find that some presumed active binaries are brighter than expected. We discuss a new statistical method to determine from observations how the formation of X-ray sources depends on the number of stellar encounters and/or on the cluster mass. We show that cluster mass is not a proxy for the encounter number, and that optical identifications are essential in proving the presence of primordial binaries among the low-luminosity X-ray sources.