093144

We propose joint NuSTAR (200 ks) and XMM (60 ks) observations of a nearby (30Mpc) hyper-luminous X-ray source (HLX) to characterize for the first time itsbroad-band spectrum which we will use to distinguish between scenarios wherethe extreme luminosity is due to sub-Eddington accretion onto an intermediatemass black hole or super-Eddington accretion onto a stellar mass compactobject. This study will extend the power of broad-band spectral characterizationwith NuSTAR to understanding the accretion state in the HLX luminosity regime. [truncated! Please see actual data for full text]