Maxime Deckers
Type Ia supernovae (SNe Ia, the thermonuclear explosions of white dwarfs) are used to determine distances in the universe. With the current tension in the H0 constant it is imperative that we eliminate all potential sources of error, one of which comes from our lack of understanding surrounding SNe Ia, and how they come to explode. Many different models have been proposed, but in order to distinguish between different model predictions we need to observe the objects within days of explosion, since all their light curves become relatively homogenous around maximum light. We can use the early light curves to probe the composition and structure of the matter ejected by the white dwarf as it explodes, which tells us about the system prior to explosion and the explosion mechanism. This work presents the largest study of the Nickel distribution of SNe Ia ejecta to date. We have found that approximately 70% of 91 objects are well matched with Chandrasekhar mass explosions, with a large degree of nickel mixing in the ejecta. The models we used most comparable to delayed detonation models, where a deflagration transitions into a detonation exploding the star. Furthermore, many objects with early ‘bumps’ have been identified in the past few years, and these are very useful for distinguishing between different origin scenarios of SNe Ia. We found that approximately 10% of objects show a flux excess in their early light curves, which could indicate a companion/CSM interaction, nickel clumps in the ejecta, or a double detonation scenario.
We perform the largest analysis of the Ni-56 distribution of SNe Ia to date. Our sample consists of 91 SN Ia, provided by The Zwicky Transient Facility (ZTF), and we use the model light curves of Chandrasekhar mass explosions with a range of Ni-56 distributions provided by Magee (2020). We find that ~70% of objects are reasonably well matched by Chandrasekhar mass explosions, see figure 3 for an example light curve of a well fit object. Furthermore, the sample is dominated by models with a high degree of Ni-56 mixing towards the surface of the ejecta as is shown in the histogram in figure 4. We compare our models to the explosion mechanisms in figures 6 & 7 and show that they are most comparable to the delayed detonation models, where a the explosion begins as a deflagration and transitions into a detonation. We also develop a method of identifying potential early excesses (bumps), and find ~10% of the objects show such an excess, which could be indicative of companion or circumstellar matter interactions, Ni-56 clumps in the outer ejecta or a detonation of a helium shell on the surface of the WD. See figure 5 for an example of such a light curve showing an excess.
Future work will further refine our method of searching for “bumps” by implementing machine learning techniques. We hope to be able to identify these objects during their initial rise to maximum so we can trigger rapid spectroscopic follow up, and learn more about the origins of SNe Ia.