Electromagnetic signatures of snIa progenitors

Although there is a nearly universal agreement that SNeIa are associated with the thermonuclear disruption of a CO white dwarf, the exact nature of their progenitors is still unknown. The nuclear runaway can start in a white dwarf gradually accreting matter from a companion star until it reaches the Chandrasekhar limit, or could be triggered by a merger of two white dwarfs in a compact binary system. The electromagnetic signatures of these two possible paths are very different. In my talk I will consider various consequences of the accretion scenario. A white dwarf with steady nuclear burning of the accreted material on its surface becomes a powerful source of soft X-ray and/or UV radiation prior to the supernova explosion. This radiation can be detected either directly - in the soft X-ray band, or indirectly - from its ionizing effect on the interstellar medium. In the low mass accretion rate regime, when hydrogen fusion is unstable, the accreting white dwarf becomes a source of classical/recurrent novae explosions, which rate is directly related to the type Ia supernova rate. Comparison of these predictions with X-ray, optical and UV observations of nearby galaxies permits to mostly exclude accreting white dwarfs exploding upon reaching the Chandrasekhar mass limit from the list of plausible candidates for type Ia supernova progenitors.