Three-dimensional morphological asymmetries in the ejecta of Cassiopeia A using a component separation method in X-rays

Abstract

Recent simulations have shown that asymmetries in the ejecta distribution of supernova remnants can still reflect asymmetries from the initial supernova explosion. Thus, their study provides a great means to test and constrain model predictions in relation to the distributions of heavy elements or the neutron star kicks, both of which are key to better understanding the explosion mechanisms in core-collapse supernovae. The use of a novel blind source separation method applied to the megasecond X-ray observations of the well-known Cassiopeia A supernova remnant has revealed maps of the distribution of the ejecta endowed with an unprecedented level of detail and clearly separated from continuum emission. Our method also provides a three-dimensional view of the ejecta by disentangling the red- and blue-shifted spectral components and associated images of the Si, S, Ar, Ca and Fe, providing insights into the morphology of the ejecta distribution in Cassiopeia A. These mappings allow us to thoroughly investigate the asymmetries in the heavy elements distribution and probe simulation predictions about the neutron star kicks and the relative asymmetries between the different elements. We find in our study that most of the ejecta X-ray flux stems from the red-shifted component, suggesting an asymmetry in the explosion. In addition, the red-shifted ejecta can physically be described as a broad, relatively symmetric plume, whereas the blue-shifted ejecta is more similar to a dense knot. The neutron star also moves directly opposite to the red-shifted parts of the ejecta similar to what is seen with44Ti. Regarding the morphological asymmetries, it appears that heavier elements have more asymmetrical distributions, which confirms predictions made by simulations. This study is a showcase of the capacities of new analysis methods to revisit archival observations to fully exploit their scientific content.