title: An X-ray-emitting blast wave from the recurrent nova RS Ophiuchi.
abstract: Stellar explosions such as novae and supernovae produce most of the heavy elements in the Universe. The onset of a nova is well understood as driven by runaway thermonuclear fusion reactions on the surface of a white dwarf in a binary star system; but the structure, dynamics and mass of the ejecta are not well known. In rare cases, the white dwarf is embedded in the wind nebula of a red-giant companion, and the explosion products plough through the nebula and produce X-ray emission. Here we report X-ray observations of such an event, from the eruption of the recurrent nova RS Ophiuchi. The hard X-ray emission from RS Ophiuchi early in the eruption emanates from behind a blast wave, or outward-moving shock wave, that expanded freely for less than 2 days and then decelerated owing to interaction with the nebula. The X-rays faded rapidly, suggesting that the blast wave deviates from the standard spherical shell structure. The early onset of deceleration indicates that the ejected shell had a low mass, the white dwarf has a high mass, and that RS Ophiuchi is therefore a progenitor of the type of supernova (type Ia) integral to studies of the expansion of the Universe.
authors.affiliation: Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, Massachusetts 02138, USA. jsokoloski@cfa.harvard.edu
authors.forename: J L
authors.initials: JL
authors.lastname: Sokoloski
authors.forename: G J M
authors.initials: GJ
authors.lastname: Luna
authors.forename: K
authors.initials: K
authors.lastname: Mukai
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Kenyon