  We have examined X-ray and optical observations of two ultra-luminous X-ray
sources, X7 and X10 in NGC4559, using XMM-Newton, Chandra and HST. The UV/X-ray
luminosity of X7 exceeds 2.1e40 erg/s in the XMM-Newton observation, and that
of X10 is >1.3e40 erg/s. X7 has both thermal and power-law spectral components.
The characteristic temperature of the thermal component is 0.12 keV. The
power-law components in the two sources both have slopes with photon index
\~2.1. A timing analysis of X7 indicates a break frequency at 28 mHz in the
power spectrum, while that for X10 is consistent with an unbroken power law.
The luminosity of the blackbody component in the X-ray spectrum of X7 and the
nature of its time variability provides evidence that this object is an
intermediate mass black hole accreting at sub-Eddington rates, but other
scenarios which require high advection efficiencies from a hollowed-out disk
might be possible. The emission from X10 can be characterised by a single
power-law. This source can be interpreted either as an intermediate mass black
hole, or as a stellar-mass black hole with relativistically-beamed Comptonised
emission. There are four optical counterparts in the error circle of X7. No
counterparts are evident in the error circle for X10.
