Testing the accreting intermediate-mass black hole hypothesis in two ULXs

We propose deep XMMNewton observations of two bright ultraluminous Xraysources, NGC 4559 X7 and NGC 5204 X1. Short observations of these ULXs haverevealed spectral soft excesses, consistent with an accretion disc around anintermediatemass black hole. We will use two diagnostic tests, only accessiblethrough high signaltonoise data, to test whether the accreting IMBH hypothesisremains viable after rigorous examination. Specifically, we will look forcurvature in the 2 10 keV Xray spectrum, which is not expected if IMBHsoperate in accretion states similar to Galactic black hole binaries, and we willplace limits on the underlying black hole masses by deriving the form of thepower spectral density for each source. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]