An expanded ultraluminous X-ray source catalogue

Vol. 659
14. Catalogs and data

An expanded ultraluminous X-ray source catalogue

Ultraluminous X-ray sources (ULXs) are X-ray sources in external galaxies with X-ray luminosities higher than 5x10^39 erg s^-1, such that they overcome the Eddington luminosity of even a ~30 solar mass black hole. In this paper, Bernadich and collaborators scrutinize the XMM-Newton-based catalog 4XMM-DR9 to identify 779 ULX candidates (brighter than 10^{39} erg s^-1) with 30 extremely bright objects (>1×10^41 erg s^−1). These extreme ULXs might indeed host intermediate-mass black holes. Starting from an existing catalog (4XMM-DR9), limited additional spectral analysis is performed on the single ULXs. The large sample allowed the authors to show that ULXs are most likely hosted in spiral galaxies. Ultraluminous X-ray sources also exist in elliptical and lenticular galaxies, where they are spectrally harder and more variable.