Hypervelocity White Dwarfs\: Telltale Signatures of a Double-Degenerate Type IaquestionMark

The progenitors of Type Ia supernovae have remained a mystery for decades. Whileit seems certain that the explosion of a C/O white dwarf is involved, thesecondary may be a nondegenerate star or another white dwarf. In the lattercase, the companion white dwarf has an orbital velocity of 11002400 km/s beforethe explosion, and retains this velocity following the explosion. A recentsearch for hypervelocity white dwarfs with Gaia has yielded several intriguingcandidates for runaway survivors from doubledegenerate Type Ia explosions. Wepropose short XMMNewton exposures of these white dwarfs to place the firstXray constraints on potential coronal Xray emission from these stars. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]