Key results from an XMM-Newton and Chandra study of a new sample of extreme ULXs from the 2XMM catalogue

TL;DR

This study analyzes 10 extreme ultraluminous X-ray sources from the 2XMM catalogue, revealing variability and complex structures, with some sources resolved into multiple components, advancing understanding of ULX properties.

Contribution

First detailed analysis of a new sample of extreme ULXs, showing variability and resolving some sources into multiple components using Chandra.

Findings

Most sources show short and long-term variability.

Some sources are resolved into multiple point sources.

Long-term spectral variability observed in several sources.

Abstract

We present highlights from a study of a sample of 10 extreme-luminosity candidate ultraluminous X-ray sources (L_X > 5 x 10^(40) erg sec^(-1)), all at distances < 100 Mpc, identified from a cross-correlation of the RC3 catalogue of galaxies with the 2XMM catalogue. Five of the sample have also been observed by Chandra. Of the 10 sources, seven reside in the disc or arms of spiral galaxies, and the remaining three are close to large elliptical galaxies. Unlike many less luminous ultraluminous X-ray sources, temporal variability is observed on short (ks) and long (year) timescales for most sources in our sample. Long term spectral variability is also evident in some sources. In one case, we use archival Chandra data to demonstrate that a hyperluminous X-ray source candidate identified by XMM-Newton is actually resolved into multiple point sources at high spatial resolution, but note that the other candidates remain unresolved under Chandra's intense scrutiny.