  Recent studies have shown that strong correlations are observed between low
frequency QPO`s and the spectral power law index for a number of black hole
candidate sources (BHC's), when these sources exhibit quasi-steady hard x-ray
emission states. The dominant long standing interpretation of QPO's is that
they are produced in and are the signature of the thermal accretion disk.
Paradoxically, strong QPO`s are present even in the cases where the thermal
component is negligible. We present a model which identifies the origin of the
QPO's and relates them directly to the properties of a compact coronal region
which is bounded by the adjustment from Keplerian to sub-Keplerian inflow into
the BH and which is primarily responsible for the observed power law spectrum.
The model also predicts the relationship between high and low frequency QPO's
and shows how BH's can be unique identified from observations of the soft
states of NS's and BHC's.
