Catalogue of ULX's line features

Accretors in this extreme regime are naturally expected to ionize copious amounts of plasma in their vicinity and launch powerful radiation-driven outflows from their discs. High spectral resolution X-ray observations [with reflection grating spectrometer (RGS) gratings onboard XMM-Newton] of a few ULXs with the best data sets indeed found complex line spectra and confirmed such extreme (0.1-0.3c) winds.

However, a search for plasma signatures in a large ULX sample with a rigorous technique has never been performed, thereby preventing us from understanding their statistical properties such as the rate of occurrence, to constrain the outflow geometry, and its duty cycle. We developed a fast method for automated line detection in X-ray spectra and applied it to the full RGS ULX archive, rigorously quantifying the statistical significance of any candidate lines.