  We model the broad-band emission from SNR RX J1713.7-3946 including, for the
first time, a consistent calculation of thermal X-ray emission together with
non-thermal emission in a nonlinear diffusive shock acceleration (DSA) model.
Our model tracks the evolution of the SNR including the plasma ionization state
between the forward shock and the contact discontinuity. We use a plasma
emissivity code to predict the thermal X-ray emission spectrum assuming the
initially cold electrons are heated either by Coulomb collisions with the shock
heated protons (the slowest possible heating), or come into instant
equilibration with the protons. For either electron heating model, electrons
reach >10^7 K rapidly and the X-ray line emission near 1 keV is more than 10
times as luminous as the underlying thermal bremsstrahlung continuum. Since
recent Suzaku observations show no detectable line emission, this places strong
constraints on the unshocked ambient medium density and on the relativistic
electron to proton ratio. For the uniform circumstellar medium (CSM) models we
consider, the low densities and high relativistic electron to proton ratios
required to match the Suzaku X-ray observations definitively rule out
pion-decay as the emission process producing GeV-TeV photons. We show that
leptonic models, where inverse-Compton scattering against the cosmic background
radiation dominates the GeV-TeV emission, produce better fits to the broad-band
thermal and non-thermal observations in a uniform CSM.
