We discuss the dynamics of a silicon surface after incidence of a short, high energy pulse in the soft X-ray
range. We focus on time-delays long enough after pulse incidence, so that the absorbed energy can be seen as a nonuniform
time-dependent heat distribution in the solid. A model is developed using techniques of non-equilibrium
hydro-thermodynamics, considering just the longitudinal and transverse acoustic phonon systems in the excited solid.
The general theory leads to Maxwell-Cattaneo partial differential equations for the material medium n(r,t) and
the energy h(r,t) volume densities; these reduce to the diffusion equation for the temperature T(r,t) and the usual
thermo-mechanical elastic equation for the strain u(r,t) on further simplification. Here we solve the Maxwell-Cattaneo
equation for T(r,t) and compare to previous results where the diffusion equation was used instead; the Maxwell-
Cattaneo equation predicts faster cooling at short (dozens of fs, say) time delays. Previously obtained results for the
strain field are briefly recalled.