Shock Breakout in 3-Dimensional Red Supergiant Envelopes

TL;DR

This study uses 3D radiation-hydrodynamic simulations to show that the shock breakout in red supergiants is longer and more variable than 1D models predict, aligning better with observations.

Contribution

First 3D simulations of shock breakout in red supergiants reveal significant differences from 1D models, highlighting the importance of large-scale fluctuations.

Findings

Shock breakout duration extends to 3-6 hours due to 3D effects.

Luminosity predictions decrease by a factor of 3-10 compared to 1D models.

3D properties invalidate using rise times to measure stellar radius.

Abstract

Using Athena++, we perform 3D Radiation-Hydrodynamic calculations of the radiative breakout of the shock wave in the outer envelope of a red supergiant (RSG) which has suffered core collapse and will become a Type IIP supernova. The intrinsically 3D structure of the fully convective RSG envelope yields key differences in the brightness and duration of the shock breakout (SBO) from that predicted in a 1D stellar model. First, the lower-density `halo' of material outside of the traditional photosphere in 3D models leads to a shock breakout at lower densities than 1D models. This would prolong the duration of the shock breakout flash at any given location on the surface to $\approx$1-2 hours. However, we find that the even larger impact is the intrinsically 3D effect associated with large-scale fluctuations in density that cause the shock to break out at different radii at different times. This substantially prolongs the SBO duration to $\approx$3-6 hours and implies a diversity of radiative temperatures, as different patches across the stellar surface are at different stages of their radiative breakout and cooling at any given time. These predicted durations are in better agreement with existing observations of SBO. The longer durations lower the predicted luminosities by a factor of 3-10 ($L_\mathrm{bol}\sim10^{44}\mathrm{erg\ s^{-1}}$), and we derive the new scalings of brightness and duration with explosion energies and stellar properties. These intrinsically 3D properties eliminate the possibility of using observed rise times to measure the stellar radius via light-travel time effects.