Abstract

Cassiopeia A is the best-observed core-collapse supernova remnant in our galaxy. Analyses of the 1 Million second Chandra Very Large Project X-ray observation and the data from infrared spectroscopy by Spitzer lead to a “complete” (within the limitations of the data quality) assessment of the elemental composition of the explosion ejecta, comprising both the reverse shocked X-ray emitting plasma and the photoionized unshocked ejecta emitting primarily in the infrared. This is the first time such a detailed census of supernova ejecta has ever been accomplished. More recently, Cassiopeia A has been observed with the James Webb Space Telescope. A first look suggests that these data corroborate and extend our previous analysis. Hard X-ray observations by NUSTAR reveal the mass and location of the radioactive nucleus 44Ti and optical imaging reveals a natal kick imparted to the compact central object (presumed to be a neutron star), anti-correlated with the 44Ti location, as expected. However, X-ray imaging reveals almost “pure” Fe knots on the east limb, presumably the ashes of alpha rich freeze out, which do not correlate so well. All these observables carry information about processes at the core of the supernova and allow us (and others) to speculate about the nature of the explosion, in ways that complement conclusions drawn from the prompt observations of supernovae.