A hyper-runaway white dwarf in Gaia DR2 as a Type Iax supernova primary
  remnant candidate
  Observations of stellar remnants linked to Type Ia and Type Iax supernovae
are necessary to fully understand their progenitors. Multiple progenitor
scenarios predict a population of kicked donor remnants and partially-burnt
primary remnants, both moving with relatively high velocity. But only a handful
of examples consistent with these two predicted populations have been observed.
Here we report the likely first known example of an unbound white dwarf that is
consistent with being the fully-cooled primary remnant to a Type Iax supernova.
The candidate, LP 93-21, is travelling with a galactocentric velocity of
v$_{gal}$ $\simeq$ 605 km s$^{-1}$, and is gravitationally unbound to the Milky
Way. We rule out an extragalactic origin. The Type Iax supernova ejection
scenario is consistent with its peculiar unbound trajectory, given anomalous
elemental abundances are detected in its photosphere via spectroscopic
follow-up. This discovery reflects recent models that suggest stellar ejections
likely occur often. Unfortunately the intrinsic faintness of white dwarfs, and
the uncertainty associated with their direct progenitor systems, makes it
difficult to detect and confirm such donors.
