Accretion states of the transient ULX in M83

In Dec 2010, Chandra revealed a previously unknown ULX in M83 where there had been no detectable X-ray source before. It has varied in flux and hardness but has remained bright for nearly two years. Our analysis shows that it is a black hole (BH) accreting from a low-mass secondary. The spectral evolution of a transient ULX as it fades is a critical test of the nature of these intriguing objects. Our goal is to determine whether it goes through the same canonical accretion states defined for Galactic BHs. We propose two 50-ks observations, separated by a few months, to identify the accretion state(s), accurately determine the physical parameters, and compare with stellar-mass BH states. This will constrain the mass of this ULX and help clarify the relation between ULXs and stellar-mass BHs.