  Using the HEXTE experiment on-board the RXTE satellite, we performed a search
for hard X-ray tails in Sco X-1 spectra. We found strong evidence for the
presence of such a non-thermal component on several occasions. Using the
PCA/RXTE we were able to track the position of the source along the Z diagram,
and we observed that the presence of the hard X-ray tail is not confined to a
particular region. However, we found a correlation between the power law index
of the non-thermal component and the position of the source in the Z diagram,
suggesting that the hard X-ray spectrum (i.e., E > 50 keV) becomes flatter as
the mass accretion rate increases. We were also able to study the temporal
variation of the appearance/absence of the hard X-ray component. With our
derived luminosities, we were also able to test the idea that X-ray
luminosities can be used to distinguish between X-ray binary systems containing
neutron stars and black holes.
