X-ray grating spectra of RS Ophiuchi in outburst

The recurrent nova RS Ophiuchi was observed five times with Chandra and XMM-Newton, on four different dates after the 2006 outburst. In the first month we detected an emission spectrum with prominent lines of H and He-like ions of metals including O, N, Si, Fe, Ne and Mg, showing a large range of plasma temperatures. At this stage the emission was originated in the red giant wind material shocked by the nova ejecta. Later spectra show a large increase in emission at longer wavelengths, peaking two months after the outburst. We attribute this to the emergence of the underlying white dwarf. Preliminary fits with NLTE white dwarf atmospheric models yield log g = 9, and T ∼800,000K, appropriate a white dwarf mass of >1.2 M _⊙. The constant bolometric luminosity phase was very short, less than three months, as expected for a white dwarf mass ≈ 1.35 M _⊙. We detected an oscillation with a period ∼35 s in March and April light curves, which may be due to the spin of the white dwarf and may represents further evidence of a very massive white dwarf, pointing at RS Oph as a likely supernova Ia progenitor.