The High Energy X-ray Probe (HEX-P): Broadband studies of ultraluminous X-ray sources

HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<10 arcsec FWHM) and broad spectral coverage (0.1-150 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR), to enable revolutionary new insights into a variety of important astrophysical problems. We will present simulations of HEX-P observations of ultraluminous X-ray sources (ULX) in nearby galaxies, showing how HEX-P will (1) study in detail populations of ULXs in a fraction of the time required by NuSTAR, pushing by a factor ~25 the high-energy sensitivity. (2) characterize their hard-energy spectrum, with much higher sensitivity than NuSTAR, looking for high-energy cyclotron resonance features; and (3) perform detailed timing studies of these sources thanks to the very low background and the enhanced response in the energy ranges where pulsations are stronger. More information on HEX-P, including the full team list, is available at https://hexp.org.