The Post-Merger Magnetized Evolution of White Dwarf Binaries: The
  Double-Degenerate Channel of Sub-Chandrasekhar Type Ia Supernovae and the
  Formation of Magnetized White Dwarfs
  Type Ia supernovae (SNe Ia) play a crucial role as standardizable
cosmological candles, though the nature of their progenitors is a subject of
active investigation. Recent observational and theoretical work has pointed to
merging white dwarf binaries, referred to as the double-degenerate channel, as
the possible progenitor systems for some SNe Ia. Additionally, recent
theoretical work suggests that mergers which fail to detonate may produce
magnetized, rapidly-rotating white dwarfs. In this paper, we present the first
multidimensional simulations of the post-merger evolution of white dwarf
binaries to include the effect of the magnetic field. In these systems, the two
white dwarfs complete a final merger on a dynamical timescale, and are tidally
disrupted, producing a rapidly-rotating white dwarf merger surrounded by a hot
corona and a thick, differentially-rotating disk. The disk is strongly
susceptible to the magnetorotational instability (MRI), and we demonstrate that
this leads to the rapid growth of an initially dynamically weak magnetic field
in the disk, the spin-down of the white dwarf merger, and to the subsequent
central ignition of the white dwarf merger. Additionally, these magnetized
models exhibit new features not present in prior hydrodynamic studies of white
dwarf mergers, including the development of MRI turbulence in the hot disk,
magnetized outflows carrying a significant fraction of the disk mass, and the
magnetization of the white dwarf merger to field strengths $\sim 2 \times 10^8$
G. We discuss the impact of our findings on the origins, circumstellar media,
and observed properties of SNe Ia and magnetized white dwarfs.
