The First Day of a Type Ia Supernova from a Double-Degenerate Binary

TL;DR

This paper models the early interaction between type Ia supernova ejecta and a white dwarf companion, revealing how the collision affects the initial light curve and observable brightness depending on viewing angle.

Contribution

It introduces detailed hydrodynamical and radiation simulations of supernova ejecta-companion interaction, providing new insights into early supernova light curves and their dependence on viewing geometry.

Findings

Hot, high-velocity ejecta produce >10^40 ergs/s luminosity in the first hours.

Shock heating causes a low-density wake extending to higher velocities.

One day after explosion, the luminosity from the wake view is 15% dimmer than normal.

Abstract

Supernovae in binary star systems involve a hydrodynamical interaction between the ejecta and a binary companion. This collision results in shock heating and a modified density structure for the ejecta, both of which affect the light curve. As highlighted by Kasen, these considerations are particularly relevant for type Ia supernovae, as the companion is expected to be Roche-lobe filling at the time of the explosion. We simulate here the interaction between type Ia supernova ejecta and a white dwarf donor using Athena++, finding the formation of a low-density wake extending to higher velocities than the unperturbed ejecta. Radiation hydrodynamics is then used to generate synthetic light curves for the first day after the explosion for a range of viewing angles. We find that the hot, high-velocity, shocked ejecta yields $L>10^{40}$ ergs/s over half the sky in the first few hours. The photosphere within the shock-heated ejecta cools and recedes in velocity space, partially obscuring it from view, as heating from radioactive nickel becomes increasingly important in driving the supernova's luminosity. By one day after the explosion, the luminosity measured by observers looking directly into the wake is dimmer than that of a normal type Ia supernova by 15 percent due to the modified density structure.