WFCAM Survey of M31 Globular Clusters: Low Mass X-ray Binaries

TL;DR

This study demonstrates that the stellar collision rate in globular clusters of M31 is a key predictor for the presence of low mass X-ray binaries, surpassing cluster mass as an indicator.

Contribution

It provides the first detailed analysis linking stellar collision rates to LMXB occurrence in M31 globular clusters, emphasizing dynamical interactions over mass or neutron star retention.

Findings

Stellar collision rate strongly correlates with LMXB presence.

Collision rate is a better predictor than cluster mass.

Results support dynamical formation of LMXBs in clusters.

Abstract

We investigate the relationship between Low Mass X-ray Binaries (LMXBs) and globular clusters (GCs) using UKIRT observations of M31 and existing Chandra, XMM-Newton, and ROSAT catalogues. By fitting King models to these data we have estimated the structural parameters and stellar collision rates of 239 of its GCs. We show a highly significant trend between the presence of a LMXB and the stellar collision rate of a cluster. The stellar collision rate is found to be a stronger predictor of which clusters will host LMXBs than the host cluster mass. We argue that our results show that the stellar collision rate of the clusters is the fundamental parameter related to the production LMXBs. This is consistent with the formation of LMXBs through dynamical interactions with little direct dependence on the neutron star retention fraction or cluster mass.