Observational properties of SNe Ia progenitors close to the explosion

Abstract

We determine the expected signal in various observational bands of Supernovae Ia progenitors just before the explosion by assuming the rotating Double Degenerate scenario. Our results are valid also for all the evolutionary scenarios invoking rotation as the driving mechanism of the accretion process as well as the evolution up to the explosion. We find that the observational properties depend mainly on the mass of the exploding object, even if the angular momentum evolution after the end of the mass accretion phase and before the onset of C-burning plays a non-negligible role. Just before the explosion the magnitude M_V ranges between 9 and 11 mag, while the colour (F225W-F555W) is about -1.64 mag. The photometric properties remain constant for a few decades before the explosion. During the last few months the luminosity decreases very rapidly. The corresponding decline in the optical bands varies from few hundredths up to one magnitude, the exact value depending on both the WD total mass and the braking efficiency at the end of the mass transfer. This feature is related to the exponentially increasing energy production which drives the formation of a convective core rapidly extending over a large part of the exploding object. Also a drop in the angular velocity occurs. We find that observations in the soft X band (0.5 -2 keV) may be used to check if the SNe Ia progenitors evolution up to explosion is driven by rotation and, hence, to discriminate among different progenitor scenarios.