Spectral Signatures of Gravitationally Confined Thermonuclear Supernova Explosions

Abstract

We consider some of the spectral and polarimetric signatures of the gravitationally 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.

Detonating Failed Deflagration Model of Thermonuclear Supernovae. II. Comparison to Observations

“…This highvelocity shell resembles the pancake structure described in the parameterized models of Kasen & Plewa (2005) except that in the Y12 model the material has a larger covering factor and a more irregular structure. Note that only silicon, and not calcium, is present in the high-velocity shell, an artifact of the approximate burner used during the deflagration phase.…”

“…One expects that, had a more complete nuclear network been used, a significant amount of calcium would also be present. Rather than speculate as to that exact amount of calcium produced, we leave the compositional structure as is, referring the reader to the studies of Kasen & Plewa (2005). Before considering the observable properties of the Y12 model, we mention a few limitations of the underlying explosion calculations.…”

The early spectral evolution of SN 2004dt

“…A possible exception to the latter could be the model of Plewa et al (2004), where the intrusion of high-velocity, intermediate-mass elements would come from the same rising plume that triggers a detonation in the outer layers (Kasen & Plewa 2005). However, the presence of a single blob would be at odds with the presence of HVFs in all SNe Ia.…”

“…This, together with the polarization data, suggests the presence of an almost spherical O layer with intrusions of intermediate-mass elements. While the finger-like structure is typically found in pure deflagration models of the explosions, Kasen & Plewa (2005) interpret the presence of Ca ii moving at high velocities as a signature of the deflagration products brought to the surface by the rising plume in the model of Plewa et al (2004), which are compressed and accelerated by the SN ejecta after the detonation has been triggered.…”

DEVIATIONS FROM AXISYMMETRY REVEALED BY LINE POLARIZATION IN THE NORMAL TYPE Ia SUPERNOVA 2004S

“…The composition and origin of this HV material remain mysterious. Suggestions in the literature have included clumps of material newly synthesized in the explosion (Wang et al 2003), signatures of a gravitationally confined detonation (Kasen & Plewa 2005), and interaction with circumstellar material (Wang et al 2003;Gerardy et al 2004;Mazzali et al 2005a). In all cases, viable models for the origin of the HV material must recognize its intrinsically 3D nature, as revealed by the spectropolarimetric line features and angle rotations.…”