Noam Soker Technion, Israel

I show that a newly estimated fraction of normal type Ia supernovae (SNe Ia) that interact within about 100 days of explosion with circumstellar material (CSM), called SNe Ia-CSM, is compatible with a recently estimated fraction of normal SNe Ia that interact with an old planetary nebula, hence, supporting the core-degenerate (CD) scenario for normal SNe Ia. According to the CD scenario, a white dwarf (WD) merges with the core of an asymptotic giant branch star at the end of common envelope evolution (CEE) and forms a massive WD remnant close to the Chandrasekhar mass. The CEE ejects a planetary nebula that the WD remnant ionizes. Most explosions occur within a merger-to-explosion delay (MED) time of less than a million years, before the planetary nebula material disperses to the interstellar medium, leading to a SN Ia inside a planetary nebula (SNIP). I discuss two plausible MED time distributions and show that the newly determined SNe Ia-CSM fraction of all normal SNe Ia, ~0.04%, is compatible with the SNIP fraction of ~80%. Therefore, although the fraction of SNe Ia-CSM is very small, it does not require a rare evolutionary pathway. I argue that SNe Ia-CSM follow the same scenario that accounts for 70%-90% of all normal SNe Ia, namely, the CD scenario.