  The emission of the white dwarf-M dwarf binary AR Sco is driven by the rapid
synchronization of its white dwarf, rather than by accretion. This requires a
comparatively large magnetic field $\sim 100$ gauss at the M dwarf and $\sim
10^8$ gauss on the white dwarf, larger than the fields of most intermediate
polars but within the range of fields of known magnetic white dwarfs. The
spindown power is dissipated in the atmosphere of the M dwarf by magnetic
reconnection, accelerating particles that produce the observed synchrotron
radiation. The displacement of the optical maximum from conjunction may be
explained either by dissipation in a bow wave as the white dwarf's magnetic
field sweeps past the M dwarf or by a misaligned white dwarf's rotation axis
and oblique magnetic moment. In the latter case the rotation axis precesses
with a period of decades, predicting a drift in the orbital phase of maximum.
Binaries whose emission is powered by synchronization may be termed
synchronars, in analogy to magnetars.
