High-entropy ejecta plumes in Cassiopeia A from neutrino-driven convection

TL;DR

This paper reports the first observational evidence of high-entropy ejecta plumes in Cassiopeia A, identified through stable Ti and Cr elements, supporting neutrino-driven convection in supernova explosions.

Contribution

It provides the first detection of Ti and Cr in high-velocity ejecta, confirming high-entropy plumes and neutrino-driven convection in a supernova remnant.

Findings

Detection of stable Ti and Cr at >5σ confidence in Cassiopeia A ejecta.

Observed Ti/Fe and Cr/Fe ratios indicate $ ext{α}$-rich freeze out.

Metal composition matches predictions for neutrino-processed ejecta.

Abstract

Recent multi-dimensional simulations suggest that high-entropy buoyant plumes help massive stars to explode. Outwardly protruding iron-rich fingers in the galactic supernova remnant Cassiopeia A are uniquely suggestive of this picture. Detecting signatures of specific elements synthesized in the high-entropy nuclear burning regime (i.e., $\alpha$-rich freeze out) would be among the strongest substantiating evidence. Here we report the discovery of such elements, stable Ti and Cr, at a confidence level greater than 5$\sigma$ in the shocked high-velocity iron-rich ejecta of Cassiopeia A. We found the observed Ti/Fe and Cr/Fe mass ratios require $\alpha$-rich freeze out, providing the first observational demonstration for the existence of high-entropy ejecta plumes that boosted the shock wave at explosion. The metal composition of the plumes agrees well with predictions for strongly neutrino-processed proton-rich ejecta. These results support the operation of the convective supernova engine via neutrino heating in the supernova that produced Cassiopeia A.