Collisionless Shocks and TeV Neutrinos before Supernova Shock Breakout from an Optically Thick Wind

TL;DR

This paper shows that in some supernovae with dense winds, a collisionless shock forms inside the wind before shock breakout, leading to early TeV neutrino emission and a hard X-ray flash, offering new insights into progenitor structure.

Contribution

It demonstrates that collisionless shocks can form deep inside optically thick winds before shock breakout, altering the expected neutrino and photon signals from supernovae.

Findings

Collisionless shocks form inside dense winds before shock breakout.

TeV neutrinos can arrive more than ten hours before photons.

A hard X-ray flash is produced at shock breakout.

Abstract

During a supernova explosion, a radiation-dominated shock (RDS) travels through its progenitor. A collisionless shock (CS) is usually assumed to replace it during shock breakout (SB). We demonstrate here that for some realistic progenitors enshrouded in optically thick winds, such as possibly SN 2008D, a CS forms deep inside the wind, soon after the RDS leaves the core, and therefore significantly before SB. The RDS does not survive the transition from the core to the thick wind when the wind close to the core is not sufficiently dense to compensate for the $r^{-2}$ dilution of photons due to shock curvature. This typically happens when the shock velocity is $\lesssim 0.1 {\rm c} \, (\frac{u_{\rm w}}{10\,{\rm km/s}}) (\frac{\dot{M}}{5 \cdot 10^{-4} \, {\rm M}_\odot {\rm /yr}})^{-1} (\frac{r_\ast}{10^{13}\,{\rm cm}})$, where $u_{\rm w}$, $\dot{M}$ and $r_\ast$ are respectively the wind velocity, mass-loss rate and radius of the progenitor star. The radiative CS results in a hard spectrum of the photon flash at breakout, which would produce an X-ray flash. Cosmic ray acceleration would start before SB, for such progenitors. A fraction of secondary TeV neutrinos can reach the observer up to more than ten hours before the first photons from breakout, providing information on the invisible layers of the progenitor.