Aspherical Supernovae: Effects on Early Light Curves

TL;DR

This paper investigates how non-spherical explosions in supernovae affect early light curves, revealing that non-radial flows and ejecta collisions significantly alter observable signals and complicate breakout emission detection.

Contribution

The study introduces a new simulation-based method to analyze non-spherical supernova explosions and their impact on early light curves, highlighting effects previously unexplored.

Findings

Non-radial flows develop in sufficiently non-spherical explosions.

These flows limit ejecta speeds and cause ejecta-ejecta collisions.

Early light curves are affected by non-spherical effects, blending breakout light with early emission.

Abstract

Early light from core-collapse supernovae, now detectable in high-cadence surveys, holds clues to a star and its environment just before it explodes. However, effects that alter the early light have not been fully explored. We highlight the possibility of non-radial flows at the time of shock breakout. These develop in sufficiently non-spherical explosions if the progenitor is not too diffuse. When they do develop, non-radial flows limit ejecta speeds and cause ejecta-ejecta collisions. We explore these phenomena and their observational implications, using global, axisymmetric, non-relativistic FLASH simulations of simplified polytropic progenitors, which we scale to representative stars. We develop a method to track photon production within the ejecta, enabling us to estimate band-dependent light curves from adiabatic simulations. Immediate breakout emission becomes hidden as an oblique flow develops. Non-spherical effects lead the shock-heated ejecta to release a more constant luminosity at a higher, evolving color temperature at early times, effectively mixing breakout light with the early light curve. Collisions between non-radial ejecta thermalize a small fraction of the explosion energy; we address emission from these collisions in a subsequent paper.