Joshua Pollin, Fionntán Callan, Stuart Sim, Christine Collins, Luke Shingles
Astrophysics Research Centre, Queen’s University Belfast, Northern Ireland
Supernovae are bright astrophysical events associated with the explosive deaths of stars. They are so luminous that individual supernovae can be observed in distant galaxies and monitored as they rise and fade over weeks to years. Aside from being spectacular events, they are vital for multiple branches of modern astrophysics: they generate many of the familiar elements, they regulate star formation in galaxies and are used as distance indicators in cosmology. Many Type Ia supernovae (SNe Ia) show a clear and well-defined relationship between their peak luminosity and the rate at which their luminosity declines and are, as such, called “normal” SNe Ia; however, due to modern large-scale transient surveys, several “peculiar” subclasses have emerged (Taubenberger 2017). Our work uses computer simulations to predict the radiation emitted by theoretical explosion models. We compare the predicted observables to observations to better understand the nature of SNe Ia and gain insight into which explosion models should be favoured or disfavoured for different classes of event. Our forward modelling strategy allows for a comprehensive understanding of SNe Ia from first principles, which aims to connect the observed diversity to underlying physical differences.
Recently, a new class of model for SNe Ia has been developed, the so-called “Dynamically Driven Double-degenerate Double-detonation” (D6) model. This combines two previous classes of models: the “Violent merger” and the “Double-detonation” models. In the “Violent merger” model, two White Dwarf (WD) stars, mainly composed of carbon and oxygen, will merge due to the emission of gravitational waves shrinking their orbits. This merging process creates hotspots that cause carbon burning, leading to a runaway thermonuclear reaction. In the “Double-detonation” model, a WD accumulates a very thin surface layer of helium via interaction with a companion star. Due to the energetic nature of the accumulation of helium, this surface layer ignites and produces an off-centre core detonation. Both the “Violent merger” and the “Double-detonation” model produced good agreement with both “normal” and “peculiar” SNe Ia. The D6 model combines aspects of both these models; initially, a thin layer of helium is ignited as the two WDs merge, which subsequentially produces an off-centre detonation on the larger WD. However, the fate of the companion remains uncertain due to the amount of helium on the surfaces of the WDs being poorly constrained.
Our investigation of the D6 model primarily focuses on how the fate of the secondary influences the synthetic observables, based on explosion models from Pakmor et al. (2022). Our simulations show (see Figure) that the synthetic light curves produced when only the primary (3DOneExpl) and both the primary and secondary WDs detonate (3DTwoExpl) produce, on average, photometry that is similar. However, our multidimensional approach also allows us to investigate the synthetic observables for different observer orientations, and we find that the 3DTwoExpl model possesses variation that is large enough to match both “normal” and “peculiar” SNe Ia. Our simulations also show that these asymmetric explosion models cannot be well represented by 1D simulations (1DOneExpl and 1DTwoExpl) as there is a large difference in the bluest filters between the 1D and 3D simulations. This reinforces that a fully multidimensional approach is needed to produce synthetic observables that accurately represent the explosion scenario. In general, the D6 model demonstrated that it could reasonably match both photometric and spectroscopic observations of “normal” SNe Ia and warrants further, more detailed investigation, especially as the fate of the secondary remains an important open question.
This work used the Cambridge Service for Data Driven Discovery (CSD3), part of which is operated by the University of Cambridge Research Computing on behalf of the STFC DiRAC HPC Facility (www.dirac.ac.uk).
References:
• Taubenberger S., 2017, in Alsabti A. W., Murdin P., eds, , Handbook of Supernovae. p. 317
• Pakmor R., et al., 2022, MNRAS, 517, 5260
Figure 1. Bolometric and UBVRI band light curves for the OneExpl and TwoExpl models. Models are displayed over 50 days and compared to the “normal” SN 2011fe (Nugent et al., 2011, Nature, 480, 344). Solid lines represent the 3D models, whereas dashed lines represent 1D simulations.