Fionntán Callan, Stuart Sim, Christine Collins, Luke Shingles, Joshua Pollin
Astrophysics Research Centre, Queen’s University Belfast, Northern Ireland
Type Ia supernovae (SNe Ia) are extremely luminous astrophysical events that arise from the thermonuclear explosions of white dwarf stars. They play a number of key roles in astrophysics including acting as cosmological distance indicators, contributing substantially to cosmic nucleosynthesis and injecting energy in galaxy evolution. Despite the significant interest in SNe Ia, the mechanisms which produce them are still poorly understood with many different explosion scenarios proposed to explain them. Modern transient surveys have also made it clear that SNe Ia are a diverse population with multiple explosion scenarios likely required to explain the various sub-classes of SNe Ia. In our DiRAC project we carry out radiative transfer computer simulations to produce predictions of light curves and spectra for various theoretical models of SNe Ia. This allows us to make direct comparisons between theoretical models and observed SNe Ia in order to better understand both the physical conditions in multiple sub-classes of SNe Ia and ultimately their origins.
Type Iax supernovae (SNe Iax) are the largest sub-class of SNe Ia estimated by Foley et al. (2013) to make up ~ 30% of the total SNe Ia rate. SNe Iax show spectroscopic differences to “normal” SNe Ia, have lower peak magnitudes and show a much larger spread in their brightness, differing by more than 4 magnitudes at peak. Previous studies have shown pure deflagration models of Chandrasekhar mass carbon-oxygen white dwarfs reproduce many of the observed characteristics of SNe Iax, making them the most promising explosion scenario to explain SNe Iax. We recently carried out a parameter study of such pure deflagration models (Lach et al., 2022) and found our model sequence was able to produce good agreement with observed SNe Iax over a wide range of luminosities, with poor agreement only found with the faintest SNe Iax. However, as was the case in previous studies (e.g. Fink et al., 2014) there are still some systematic differences between pure deflagration models and observed SNe Iax. In particular, model light curves and spectra produce good agreement with observed SNe Iax at early times but at later times the light curves decline too quickly in comparison to observed SNe Iax. This systematic difference becomes increasingly prominent when comparing to fainter SNe Iax and in redder filter bands.
Late time observations of SNe Iax have suggested there is a luminous remnant left behind after the explosion (e.g. Foley et al., 2014). Such a luminous remnant is also predicted by pure deflagration explosion models including those from our parameter study (Lach et al., 2022). However, previous studies have not included radiation from this luminous remnant in full radiative transfer simulations. In our project we have recently been investigating whether including the radiation emitted by such a luminous remnant can help explain the systematic differences between our pure deflagration models and observed SNe Iax. From the figure it is clear that including the radiation predicted for the luminous remnant in our radiative transfer simulations significantly improves agreement between our models and observed SNe Iax, for both bright and intermediate luminosity SNe Iax. This strengthens the case that SNe Iax originate from deflagration explosions which do not fully unbind the white dwarf and leave behind a luminous remnant. This work will be submitted for publication in the coming weeks (Callan et al., 2023, in prep). We also intend to carry out future work focussing on how our radiative transfer simulations are impacted by a more detailed treatment of the remnant in the explosion simulations.
This work made use of 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).
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