LMC X-3: The best test of accretion disc models

The persistent black hole binary LMC X-3 is the best system on which to test theoretical models on the shape of the accretion disc spectrum. This is due to the combination of very low absorbing column density along this line of sight, which allows the shape of the disc emission to be constrained at low energies, and its mass accretion rate, which varies by a factor 10, giving a sequence of disc dominated spectra 0.05-0.5 L/LEdd. However, there is currently only 1 good XMM-Newton observation of this source, at close to its peak luminosity. We propose an additional 4 observations which will give a sequence of disc spectra at different luminosities, enabling us to critically test the best current disc models and get the most robust constraints on black hole spin.