The lonely white dwarf scenarios for type Ia supernovae

I will present the newly defined lonely white dwarf (WD) scenarios for type Ia supernovae (SNe Ia) and discuss their implications for normal and peculiar SNe Ia. In the lonely WD scenarios, there is only a WD without any close companion at the explosion time. The WD formation is by the merger of two WDs in the MED-double degenerate (MED-DD) scenario or the merger of a WD with the core of an AGB star in the core degenerate (CD) scenario; in both, there is a merger to explosion delay (MED) time. The CD scenario nicely accounts for axisymmetric supernova remnants (e.g., the point symmetric SNR G1.9+0.3) by the explosion of the WD inside a planetary nebula. I will present my view that the lonely WD scenarios account for all normal SNe Ia and some peculiar SNe Ia (e.g., the historical SN Iax of 1181 AD with a spherical ejecta). The other scenarios, which have a close companion at the explosion time (the single degenerate, the double degenerate without a MED time, and the double detonation scenarios), lead to peculiar SNe Ia. The CD scenario has a relatively short time delay from star formation, a property that has implications for the observations of SNe Ia at high redshifts. I will present new observational support for the lonely WD scenarios that will most likely advance our understanding of SNe Ia.