A Type Ia supernova at the heart of superluminous transient SN 2006gy
  Superluminous supernovae radiate up to 100 times more energy than normal
supernovae. The origin of this energy and the nature of their stellar
progenitors are poorly understood. We identify neutral iron lines in the
spectrum of one such transient, SN 2006gy, and show that they require a large
mass of iron (>~0.3 Msun) expanding at 1500 km/s. We demonstrate that a model
of a standard Type Ia supernova hitting a shell of circumstellar material
produces a light curve and late-time iron-dominated spectrum that match SN
2006gy. In such a scenario, common envelope evolution of the progenitor system
can synchronize envelope ejection and supernova explosion and may explain these
bright transients.
