X- and γ-ray studies of Cas A: exposing core collapse to the core

Abstract In this review of X-ray and gamma-ray observations of Cas A, evidence is discussed that Cas A was a Type Ib supernova of a Wolf-Rayet star with a main sequence mass between 22 and 25M⊙, that exploded after stellar wind loss had reduced its mass to ∼6M⊙. The observed kinematics and the high 44Ti yield indicate that the supernova explosion was probably asymmetric, with a kinetic energy of ∼2×1051 erg.