A Large Catalogue of Ultraluminous X-ray Source Candidates in Nearby Galaxies

TL;DR

This paper presents a comprehensive catalogue of 475 ULX candidates from the 2XMM survey, analyzes their spectral features, and discusses how to distinguish different physical models using high-quality data.

Contribution

It provides the largest ULX candidate catalogue to date and explores spectral features to differentiate physical interpretations.

Findings

Catalogue includes 655 detections of 475 sources.

Spectral turnover around 6 keV observed in high-quality ULX data.

Potential to distinguish reflection and Comptonisation models observationally.

Abstract

Since their discovery, Ultraluminous X-ray sources (ULXs) have attracted attention due to their combination of extreme luminosities and extra-nuclear locations. However, they are a fairly rare phenomenon, and attempts to investigate the general properties of the population have been hindered by a relative lack of known sources. Here, we present a large catalogue of ULX candidates including 655 detections of 475 discrete sources, based on the 2XMM Serendipitous Survey. To demonstrate the potential of such a resource, we present some scientific analysis of this population, focusing on the spectral turnover seen, often at ~6 keV, in the highest quality ULX data. We also demonstrate how the recent reflection and Comptonisation interpretations of this feature may be distinguished observationally in the future, specifically using NGC 4517 ULX1, a previously unanalysed source with high quality data, as an example case.