A Multi-Mission Catalogue of Ultraluminous X-ray Source Candidates
  We present a new, multi-mission catalogue of ultraluminous X-ray source (ULX)
candidates, based on recent data releases from each of the XMM-Newton, Swift
and Chandra observatories (the 4XMM-DR10, 2SXPS and CSC2 catalogues,
respectively). This has been compiled by cross-correlating each of these X-ray
archives with a large sample of galaxies primarily drawn from the HyperLEDA
archive. Significant efforts have been made to clean the sample of known
non-ULX contaminants (e.g. foreground stars, background AGN, supernovae), and
also to identify ULX candidates that are common to the different X-ray
catalogues utilized, allowing us to produce a combined 'master' list of unique
sources. Our sample contains 1843 ULX candidates associated with 951 different
host galaxies, making it the largest ULX catalogue compiled to date. Of these,
689 sources are catalogued as ULX candidates for the first time. Our primary
motivation is to identify new sources of interest for detailed follow-up
studies, and within our catalogue we have already found one new extreme ULX
candidate that has high S/N data in the archive: NGC 3044 ULX1. This source has
a peak luminosity of $L_{\rm{X,peak}} \sim 10^{40}$ erg s$^{-1}$, and the
XMM-Newton spectrum of the source while at this peak flux is very similar to
other, better-studied extreme ULXs that are now understood to be local examples
of super-Eddington accretion. This likely indicates that NGC 3044 ULX1 is
another source accreting at super-Eddington rates. We expect that this
catalogue will be a valuable resource for planning future observations of ULXs
- both with our current and future X-ray facilities - to further improve our
understanding of this enigmatic population.
