Thermonuclear (type Ia) supernovae are explosions in accreting white dwarfs, but the exact scenario leading to these explosions is still unclear. An important step to clarify this point is to understand the behaviour of accreting white dwarfs in clos
e binary systems. The characteristics of the white dwarf (mass, chemical composition, luminosity), the accreted material (chemical composition) and those related with the properties of the binary system (mass accretion rate), are crucial for the further evolution towards the explosion. An analysis of the outcome of accretion and the implications for the growth of the white dwarf towards the Chandrasekhar mass and its thermonuclear explosion is presented.
The recurrent nova RS Oph experienced an outburst in 2006, 21 years after its previous explosion in 1985, as expected. It was observed at almost all wavelengths, and important information about its properties is still being extracted. We present theo
retical models of the explosion of this fascinating object, which indicate that the mass of the accreting white dwarf should be very close to the Chandrasekhar mass, to allow for such a short recurrence period. In addition, since models suggest that this nova ejects less mass than it accretes, it is an excellent candidate for a thermonuclear supernova explosion, in about $10^5-10^7$ years from now. We also analyze the emission of soft gamma-rays by RS Oph detected with the BAT instrument onboard Swift, and with the PCA onboard RXTE. We rule out that this emission has its origin in radioactive decays in the expanding nova envelope.
