Swift Observations of the 2006 Outburst of the Recurrent Nova RS Ophiuchi. III. X-Ray Spectral Modeling

Following the Swift X-ray observations of the 2006 outburst of the recurrent nova RS Ophiuchi, we developed hydrodynamical models of mass ejection from which the forward shock velocities were used to estimate the ejecta mass and velocity. In order to further constrain our model parameters, we present synthetic X-ray spectra from our hydrodynamical calculations, which we compare to the Swift data. An extensive set of simulations was carried out to find a model that best fits the spectra up to 100 days after outburst. We find a good fit at high energies but require additional absorption to match the low energy emission. We estimate the ejecta mass to be in the range (2-5) × 10^-7 M _sun and the ejection velocity to be greater than 6000 km s^-1 (and probably closer to 10, 000 km s^-1). We also find that estimates of shock velocity derived from gas temperatures via standard model fits to the X-ray spectra are much lower than those of the true shock velocities.