We present a new, multimission 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 active galactic nuclei, 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 LX,peak ∼ 1040 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.

We have recently published a catalog of 1843 candidate ultraluminous X-ray sources (ULXs). This is the largest catalog of ULXs to date and was built by cross-correlating recent serendipitous source catalogs from the XMM-Newton, Swift, and Chandra observatories with a large sample of galaxies, primarily from HyperLEDA. The catalog contains 71 hyperluminous X-ray source (HLX) candidates, the most extreme members of the ULX population with luminosities above 10 41 erg s −1 . These sources are often considered the best candidates for intermediate-mass black hole (IMBH) accretors and include the archetypal IMBH candidate ESO 243-49 HLX-1. However, the most luminous of the known pulsating ULXs, NGC 5907 ULX1, is also an HLX at its brightest.We demonstrate that these two objects occupy distinct areas of the hardness-intensity parameter space, and use this to contextualize the results from a pilot study of three data-rich examples of the 42 HLXs we select as the best candidates based on their multi-wavelength counterparts and X-ray data quality. We briefly discuss the implications of this work.