# Explaining the early excess emission of the Type Ia supernova 2018oh by the interaction of the ejecta with disk-originated matter (DOM)

## TL;DR

This paper proposes that the early excess emission observed in SN 2018oh is best explained by the interaction between supernova ejecta and disk-originated matter from a white dwarf merger, supporting the double degenerate scenario.

## Contribution

It demonstrates that ejecta-DOM interaction better fits the early light curve of SN 2018oh than ejecta-companion interaction, highlighting the role of double degenerate mergers in early supernova emission.

## Key findings

- Ejecta-DOM interaction fits the early light curve better than ejecta-companion interaction.
- Ejecta-DOM interaction explains the linear rise in the light curve.
- No hydrogen or helium lines predicted by ejecta-DOM interaction, consistent with observations.

## Abstract

We explain the early excess emission of the Type Ia supernova 2018oh by an interaction of the supernova ejecta with disk-originated matter (DOM). Such DOM can form in the merger process of two white dwarfs (WDs) in the double degenerate scenario of Type Ia supernovae (SNe Ia). We find that an ejecta-DOM interaction can fit the early light curve of SN 2018oh better than an ejecta-companion interaction in the single degenerate scenario. By composing the DOM from two components that were ejected in the merger process with two different velocities, we show that the ejecta-DOM interaction can account for the linear rise in the light curve, while the ejecta-companion interaction predicts too steep a rise. In addition, the ejecta-DOM interaction does not predict the presence of hydrogen and helium lines in nebular spectra, and hence does not suffer from this major drawback of the ejecta-companion model. We consider the ejecta-DOM interaction to be the most likely explanation for the early excess emission in SN 2018oh. By that we show that the double degenerate scenario can account for early excess emission in SNe Ia.