Low-Mass X-ray Binaries and Globular Clusters in Centaurus A

TL;DR

This study investigates the relationship between globular cluster properties and low-mass X-ray binaries in Centaurus A, revealing that central density and size are key factors influencing LMXB presence.

Contribution

It provides new insights into how the structural parameters of globular clusters affect the likelihood of hosting LMXBs, emphasizing the importance of central density and size.

Findings

GCs with LMXBs are denser and more compact.

Higher encounter rates correlate with LMXB presence.

Central density and size are fundamental in LMXB occurrence.

Abstract

We present results of Hubble Space Telescope and Chandra X-ray Observatory observations of globular clusters (GCs) and low-mass X-ray binaries (LMXBs) in the central regions of Centaurus A. Out of 440 GC candidates we find that 41 host X-ray point sources that are most likely LMXBs. We fit King models to our GC candidates in order to measure their structural parameters. We find that GCs that host LMXBs are denser and more compact, and have higher encounter rates and concentrations than the GC population as a whole. We show that the higher concentrations and masses are a consequence of the dependence of LMXB incidence on central density and size plus the general trend for denser GCs to have higher masses and concentrations. We conclude that neither concentration nor mass are fundamental variables in determining the presence of LMXBs in GCs, and that the more fundamental parameters relate to central density and size.