  We present three spectra of Cygnus X-1 in the low/hard state from 3-1000 keV
produced with RXTE and OSSE. We demonstrate that a pure thermal Comptonization
model, with Compton reflection fits the data well, with coronal temperatures of
about 90 keV, optical depths of about 1.3, and reflection fractions of about
0.25 $\times$ 2$\pi$. We find that no additional components are necessary to
fit the data, although the presence of an additional non-thermal component does
result in a marginal improvement to the goodness of the fit. Two of the
observations are fit better by an almost purely non-thermal Comptonization
model with $\Gamma_{inj}$ of $\sim$ 3.2 for the electrons and the other
parameters essentially the same as for the thermal model, while the third
observation is also consistent with this model. Observations that could break
this degeneracy are discussed. We also demonstrate that the low reflection
parameter (i.e. $R/2\pi<1$) is due to a lack of strong curvature in the 30-50
keV range of the spectrum and not due to ionization effects. The spectrum
changes very little over the three weeks of the observations, in accordance
with a three week correlation timescale found in the All Sky Monitor data. We
show that for a purely thermal corona, the radius of the corona must be between
$3\times 10^6$ and $1.5\times 10^{10}$ cm, while the radius of a hybrid corona
or a purely non-thermal corona is constrained to be between $10^8$ and $10^9$
cm.
