Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: III. X-ray spectral modelling

TL;DR

This study models the X-ray spectra of the 2006 RS Ophiuchi outburst using hydrodynamical simulations to estimate ejecta properties and improve understanding of shock velocities in recurrent novae.

Contribution

It introduces synthetic X-ray spectra from hydrodynamical models to better interpret Swift observations of nova outbursts, refining ejecta mass and velocity estimates.

Findings

Ejecta mass estimated between 2-5 x 10^{-7} solar masses.

Ejection velocity likely exceeds 6000 km/s, possibly near 10,000 km/s.

Standard spectral fits underestimate true shock velocities.

Abstract

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, here 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 which 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) x 10^{-7} solar masses and the ejection velocity to be greater than 6000 km/s (and probably closer to 10,000 km/s). 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 the true shock velocities.