Determine whether Cas A’s detected 44Ti originated in the oxygen layer

Determine whether the 44Ti detected in Cassiopeia A is associated with ejecta originating from the oxygen layer, particularly material processed in a pre-supernova oxygen–carbon shell merger.

Background

The paper discusses theoretical models in which substantial 44Ti is synthesized before core collapse during an oxygen–carbon shell merger. Such material should retain some spatial and kinematic association with oxygen-layer products, including oxygen-, silicon-, and argon-rich ejecta, although multidimensional mixing and shock interaction can obscure a one-to-one correspondence.

Earlier observational tests focused on whether a potentially extended outer component of merger-produced 44Ti would remain below detection thresholds. The paper identifies as unresolved whether the 44Ti actually detected in Cassiopeia A is associated with oxygen-layer ejecta and investigates this issue through comparisons with X-ray, infrared, and three-dimensional ejecta distributions. The results support a mixed origin but do not uniquely establish the provenance of every detected 44Ti component.

References

Moreover, because their observational test concerns a potentially undetected outer component, it leaves open whether the ${44}$Ti actually detected in Cas A is associated with ejecta originating from the oxygen layer.

— Testing a Pre-Supernova Contribution to $^{44}$Ti in Cassiopeia A  (2609.16826 - Sato et al., 15 Sep 2026) in Section 1, Introduction

Whether such inhomogeneities survive the explosion and remain observable in the resulting supernova remnant is not well understood.

— Remnant-wide mapping of heterogeneous presupernova burning histories in the O-rich ejecta of Cassiopeia A  (2610.09612 - Kuboike et al., 7 Oct 2026) in Abstract; see also Section 1, Introduction