  Slim-disk models describe accretion flows at high luminosities, while
reducing to the standard thin disk form in the low luminosity limit. We have
developed a new spectral model, slimbb, within the framework of XSPEC, which
describes fully relativistic slim-disk accretion and includes photon
ray-tracing that starts from the disk photosphere, rather than the equatorial
plane. We demonstrate the features of this model by applying it to RXTE spectra
of the persistent black-hole X-ray binary LMC X-3. LMC X-3 has the virtues of
exhibiting large intensity variations while maintaining itself in soft spectral
states which are well described using accretion-disk models, making it an ideal
candidate to test the aptness of slimbb. Our results demonstrate consistency
between the low-luminosity (thin-disk) and high luminosity (slim-disk) regimes.
We also show that X-ray continuum-fitting in the high accretion rate regime can
powerfully test black-hole accretion disk models.
