A Chandra X-ray Survey of Ejecta in the Cassiopeia A Supernova Remnant

TL;DR

This study uses extensive Chandra X-ray observations to analyze the ejecta distribution in Cassiopeia A, revealing multiple shocks, element distributions, and insights into the supernova explosion dynamics.

Contribution

It provides a detailed spatial and compositional analysis of the ejecta in Cassiopeia A, including mass estimates and the identification of two Fe ejecta populations, advancing understanding of supernova remnant evolution.

Findings

Ejecta experienced multiple secondary shocks.

Total shocked Fe mass is about 0.13 solar masses.

Fe ejecta are located outside the remnant's center, indicating hydrodynamic instabilities.

Abstract

We present a survey of the X-ray emitting ejecta in the Cassiopeia A supernova remnant based on an extensive analysis of over 6000 spectral regions extracted on 2.5-10" angular scales using the Chandra 1 Ms observation. We interpret these results in the context of hydrodynamical models for the evolution of the remnant. The distributions of fitted temperature and ionization age, and the implied mass coordinates, are highly peaked and suggest that the ejecta were subjected to multiple secondary shocks following reverse shock interaction with ejecta inhomogeneities. Based on the fitted emission measure and element abundances, and an estimate of the emitting volume, we derive masses for the X-ray emitting ejecta and also show the distribution of the mass of various elements over the remnant. An upper limit to the total shocked Fe mass visible in X-rays appears to be roughly 0.13 M_sun, which accounts for nearly all of the mass expected in Fe ejecta. We find two populations of Fe ejecta, that associated with normal Si-burning and that possibly associated with alpha-rich freeze-out, with a mass ratio of approximately 2:1. Essentially all of the observed Fe (both components) lies well outside the central regions of the SNR, possibly having been ejected by hydrodynamic instabilities during the explosion. We discuss this, and its implications for the neutron star kick.