We consider some of the spectral and polarimetric signatures of the
gravitational confined detonation scenario for Type Ia supernova explosions. In
this model, material produced by an off-center deflagration (which itself fails
to produce the explosion) forms a metal-rich atmosphere above the white dwarf
surface. Using hydrodynamical simulations, we show that this atmosphere is
compressed and accelerated during the subsequent interaction with the supernova
ejecta. This leads ultimately to the formation of a high-velocity pancake of
metal-rich material that is geometrically detached from the bulk of the ejecta.
When observed at the epochs near maximum light, this absorbing pancake produces
a highly blueshifted and polarized calcium IR triplet absorption feature
similar to that observed in several Type~Ia supernovae. We discuss the
orientation effects present in our model and contrast them to those expected in
other supernova explosion models. We propose that a large sample of
spectropolarimetric observations can be used to critically evaluate the
different theoretical scenarios.Comment: 4 pages, 3 figures. To appear in ApJ Letters. For higher resolution
images and movies see http://panisse.lbl.gov/~dnkasen/gcd.htm
