Supersoft X-ray Light Curve of RS Oph -- The White Dwarf Mass is Now Increasing

TL;DR

This study presents the first complete supersoft X-ray light curve of RS Oph's 2006 outburst, indicating the white dwarf's mass is increasing, supporting its potential as a Type Ia supernova progenitor.

Contribution

It provides the first detailed X-ray light curve analysis and models the white dwarf mass growth during the nova outburst.

Findings

Supersoft X-ray phase lasted from 30 to 85 days post-outburst.

Estimated white dwarf mass is 1.35 solar masses with a growth rate of (0.5-1)×10^{-7} solar masses per year.

The long X-ray duration suggests helium layer accumulation, indicating mass increase.

Abstract

The recurrent nova RS Ophiuchi, one of the candidates for Type Ia supernova progenitors, underwent the sixth recorded outburst in February 2006. We report a complete light curve of supersoft X-ray that is obtained for the first time. A numerical table of X-ray data is provided. The supersoft X-ray flux emerges about 30 days after the optical peak and continues until about 85 days when the optical flux shows the final decline. Such a long duration of supersoft X-ray phase can be naturally understood by our model in which a significant amount of helium layer piles up beneath the hydrogen burning zone during the outburst, suggesting that the white dwarf mass is effectively growing up. We have estimated the white dwarf mass in RS Oph to be 1.35 \pm 0.01 M_\sun and its growth rate to be about (0.5-1) \times 10^{-7} M_\sun yr^{-1} in average.