Speaker
Description
Type Ia supernovae (SNe Ia) play a key role in cosmic nucleosynthesis and serve as cosmological distance indicators. There is consensus that SNe Ia originate from the thermonuclear explosions of white dwarfs (WDs) but the explosion mechanism(s) that produce them are still not understood. In this talk I will focus on potential observational signatures for two different SNe Ia explosion scenarios, which provide a critical test for whether these scenarios should be supported or ruled out as explanations for SNe Ia. I will first discuss the pure deflagrations scenario for Chandrasekhar mass carbon-oxygen (CO) WDs, suggested as the most promising explanation for the most numerous, peculiar sub-class of SNe Ia, known as type Iax supernovae (SNe Iax). Many pure deflagration models do not fully unbind the WD leaving behind a remnant polluted with a significant amount of $^{56}\mathrm{Ni}$, which is therefore expected to be luminous. Such a luminous remnant has also been suggested to have been observed for multiple SNe Iax. Previous studies of pure deflagration models have not however accounted for luminous remnants in early time radiative transfer simulations, possibly explaining why the model light curves decline significantly too quickly after peak compared to observed SNe Iax. In this talk I will present radiative transfer simulations for a selection of models from our pure deflagration sequence in which the contribution from a luminous remnant is included. I will comment on how the inclusion of a luminous remnant impacts comparisons with observed SNe Iax and the implications of including this potential observational signature of pure deflagration models on their case as the explanation for the SNe Iax sub-class. Another leading theoretical model for SNe Ia is the “double-detonation” scenario in which the explosion of a CO WD is triggered by ignition of a surface layer of helium. Recent simulations have demonstrated that double detonation models have the promise to account for SNe Ia across a range of luminosities including normal and peculiar SNe Ia (but not SNe Iax). Additionally, several observed SNe Ia have been suggested to arise from this scenario. A defining property of double detonation models is unburnt helium in their outer ejecta – determining whether this helium should produce observable signatures is therefore a critical test of this scenario. Our group recently published results from a radiative transfer simulation of a double detonation model in which a full NLTE treatment of the plasma conditions was utilised, enabling potential helium features to be accurately simulated. I will summarise the key findings of this study, in particular commenting on the helium features predicted by the simulations, their comparisons with observations and the potential of helium spectral features as a possible observational signature of the double detonation scenario.
