The Cassiopeia A Supernova was of Type IIB

TL;DR

This study analyzes a light echo from Cassiopeia A to determine it was a Type IIb supernova, revealing details about its progenitor and explosion, thus advancing understanding of supernova physics.

Contribution

The paper provides the first optical spectrum of Cassiopeia A's supernova from a light echo, conclusively identifying it as Type IIb and clarifying its progenitor's nature.

Findings

Cassiopeia A was a Type IIb supernova

Progenitor was a red supergiant with a stripped helium core

Links explosion properties to remnant characteristics

Abstract

Cassiopeia A is one of the youngest supernova remnants known in the Milky Way and a unique laboratory for supernova physics. We present an optical spectrum of the Cassiopeia A supernova near maximum brightness, obtained from observations of a scattered light echo - more than three centuries after the direct light of the explosion swept past Earth. The spectrum shows that Cassiopeia A was a type IIb supernova and originated from the collapse of the helium core of a red supergiant that had lost most of its hydrogen envelope prior to exploding. Our finding concludes a longstanding debate on the Cassiopeia A progenitor and provides new insight into supernova physics by linking the properties of the explosion to the wealth of knowledge about its remnant.