The Detonation Mechanism of the Pulsationally-Assisted Gravitationally-Confined Detonation Model of Type Ia Supernovae

Astronomy and Astrophysics – Astrophysics – High Energy Astrophysical Phenomena

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44 pages, 8 figures; submitted to ApJ

Scientific paper

We describe the detonation mechanism comprising the "Pulsationally Assisted" Gravitationally Confined Detonation (GCD) model of Type Ia supernovae (SNe Ia). This model is analogous to the previous GCD model reported in Jordan (2008); however, the chosen initial conditions produce a substantively different detonation mechanism, resulting from a larger energy release during the deflagration phase. The resulting final energy releases and nickel-56 yields conform better to observational values than is the case for the "classical" GCD models. In the present class of models, the ignition of a deflagration phase leads to a rising, burning plume of ash. The ash breaks out of the surface of the white dwarf, flows laterally around the star, and converges on the collision region at the antipodal point from where it broke out. The amount of energy released during the deflagration phase is enough to cause the star to rapidly expand, so that when the ash reaches the antipodal point, the surface density is too low to initiate a detonation. Instead, as the ash flows into the collision region (while mixing with surface fuel) the star reaches its maximally expanded state and then contracts. The stellar contraction acts to increase the density of the star, including the density in the collision region. This both raises the temperature and density of the fuel-ash mixture in the collision region and ultimately leads to thermodynamic conditions that produce a detonation. We demonstrate this mechanism with three 3-dimensional (3D), full star simulations of this model using the FLASH code, varying the initial offset of the ignition points for each model. The simulations are characterized by nuclear energy releases ranging from 38% to 78% of the binding energy of the white dwarf during the deflagration phase. We show that the conditions for detonation are achieved in all three of the models.

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