The Stellar Population Around the Intermediate Mass Black Hole ESO 243-49 HLX-1

We request joint XMM-Newton and HST observations of the best intermediate mass black hole candidate HLX-1. Recent HST and Swift observations found the broadband spectral energy distribution was well described by an irradiated accretion disc plus a stellar population. However, degeneracies in the models resulted in two acceptable solutions with dramatically different parameter values. We request two observations to be performed with XMM-Newton and the HST at different X-ray luminosities in order to break these model degeneracies using the variability of the disc emission. With these observations we will be able to determine the nature of the environment around the black hole, test formation theories for HLX-1, and rule out beaming as the origin of the extreme luminosities.