State transitions of the ULX in M83

We will study a transient ultraluminous X-ray source (ULX) in M83, which went into outburst in 2010 and is now evolving towards the luminosity range of ordinary stellar-mass black holes. We propose an XMM-Newton and HST study: a) to model the spectral state evolution during the decline, and discover how the ULX regime is linked to the sub-Eddington accretion states of Galactic BHs; b) to determine or constrain the mass of the BH, from X-ray spectroscopy; c) to quantify the properties of the irradiated disk, and its response to variable X-ray illumination from new HST WFC3 imagery.