Near-Chandrasekhar-Mass Type Ia Supernovae from the Double-Degenerate
  Channel
  Recent observational evidence has demonstrated that white dwarf (WD) mergers
are a highly efficient mechanism for mass accretion onto WDs in the galaxy. In
this paper, we show that WD mergers naturally produce highly-magnetized,
uniformly-rotating WDs, including a substantial population within a narrow mass
range close to the Chandrasekhar mass ($M_{\rm Ch}$). These near-$M_{\rm Ch}$
WD mergers subsequently undergo rapid spin up and compression on a $\sim 10^2$
yr timescale, either leading to central ignition and a normal SN Ia via the DDT
mechanism, or alternatively to a failed detonation and SN Iax through pure
deflagration. The resulting SNe Ia and SNe Iax will have spectra, light curves,
polarimetry, and nucleosynthetic yields similar to those predicted to arise
through the canonical near-$M_{\rm Ch}$ single degenerate (SD) channel, but
with a $t^{-1}$ delay time distribution characteristic of the double-degenerate
(DD) channel. Furthermore, in contrast to the SD channel, WD merger
near-$M_{\rm Ch}$ SNe Ia and SNe Iax will not produce observable companion
signatures. We discuss a range of implications of these findings, from SNe Ia
explosion mechanisms, to galactic nucleosynthesis of iron peak elements
including manganese.
