  We explore a simple model for the high luminosity of SN 2006gy involving
photon diffusion of shock-deposited thermal energy. The distinguishing property
of the model is that the large ``stellar'' radius of 160 AU required to prevent
adiabatic losses is not the true stellar radius, but rather, the radius of an
opaque, unbound circumstellar envelope, created when 10 Msun was ejected in the
decade before the supernova in an eruption analogous to that of eta Carinae.
The supernova light is produced primarily by diffusion of thermal energy
following the passage of the blast wave through this shell. This model differs
from traditional models of supernova debris interacting with external CSM in
that here the shell is optically thick and the escape of radiation is delayed.
We show that any model attempting to account for SN2006gy's huge luminosity
with radiation emitted by ongoing CSM interaction fails for the following basic
reason: the CSM density required to achieve the observed luminosity makes the
same circumstellar envelope opaque, forcing a thermal diffusion solution. In
our model, the weaker CSM interaction giving rise to SN2006gy's characteristic
Type IIn spectrum and soft X-rays is not linked to the power source of the
visual continuum; instead, it arises after the blast wave breaks free of the
opaque shell into the surrounding wind. While a simple diffusion model can
explain the gross properties of the early light curve of SN2006gy, it predicts
that the light curve must plummet rapidly at late-times, unless an additional
power source is present.
