  The Suzaku observation of LMC X-3 gives the best data to date on the shape of
the accretion disk spectrum. This is due to the combination of very low
absorbing column density along this line of sight which allows the shape of the
disk emisison to be constrained at low energies by the CCD's, while the tail
can be simultaneously determined up to 30 keV by the high energy detectors.
These data clearly demonstrate that the observed disk spectrum is broader than
a simple 'sum of blackbodies', and relativistic smearing of the emission is
strongly required. However, the intrinsic emission should be more complex than
a (color-corrected) sum of blackbodies as it should also contain photo-electric
absorption edges from the partially ionised disk photosphere. These are
broadened by the relativistic smearing, but the models predict ~ 3-5 per cent
deviations for 1/3- 1 solar abundance around the edge energies, significantly
stronger than observed. This indicate that the models need to include more
physical processes such as self-irradiation, bound-bound (line) absorption,
and/or emission from recombination continuua and/or lines. Alternatively, if
none of these match the data, it may instead require that the accretion disk
density and/or emissivity profile with height is different to that assumed.
Thus these data demonstrate the feasibility of observational tests of our
fundamental understanding of the vertical structure of accretion disks.
