Testing a Pre-Supernova Contribution to 44Ti in Cassiopeia A
Abstract
The radioactive isotope 44Ti in Cassiopeia A has been used as a tracer of the innermost ejecta and explosion asymmetries in core-collapse supernova explosions. However, recent stellar-evolution models suggest substantial 44Ti may also be synthesized prior to explosion during oxygen-carbon (O-C) shell mergers, a process proposed for the Cas A progenitor. We investigate this pre-supernova contribution by combining NuSTAR measurements of the spatial and kinematic distribution of 44Ti with X-ray and infrared ejecta diagnostics. The low- and intermediate-velocity 44Ti components are more closely associated with O-layer tracers than with shocked Fe-rich material. If the 44Ti associated with the O-layer tracers was synthesized prior to core collapse, it could contribute up to ∼7×10−5 M⊙, about half of the total. We find that this amount of 44Ti can be produced in O-C shell-merger models with ingestion rates and convective velocities higher than those in standard one-dimensional stellar-evolution calculations. Stable Fe-group abundance ratios measured with XRISM provide an additional constraint on the explosive contribution, as three-dimensional models with larger 44Ti yields tend to predict Ti/Fe and Mn/Cr ratios above the observed values. These results suggest that both pre-supernova shell-merger nucleosynthesis and explosive burning contribute to the observed 44Ti.
Related
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BibTeX
@misc{sato2026testing,
title = {{Testing a Pre-Supernova Contribution to $^44$Ti in Cassiopeia A}},
author = {Toshiki Sato and Joshua Issa and Falk Herwig and Yui Kuboike and J. Martin Laming and Kai Matsunaga and Ryo Sawada},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.16826},
eprint = {2609.16826},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.16826},
}
RIS
TY - UNPB
TI - Testing a Pre-Supernova Contribution to ^44Ti in Cassiopeia A
AU - Toshiki Sato
AU - Joshua Issa
AU - Falk Herwig
AU - Yui Kuboike
AU - J. Martin Laming
AU - Kai Matsunaga
AU - Ryo Sawada
PY - 2026
DA - 2026/09/15
PB - arXiv
DO - 10.48550/arxiv.2609.16826
UR - https://arxiv.org/abs/2609.16826
AB - The radioactive isotope ^44Ti in Cassiopeia A has been used as a tracer of the innermost ejecta and explosion asymmetries in core-collapse supernova explosions. However, recent stellar-evolution models suggest substantial ^44Ti may also be synthesized prior to explosion during oxygen-carbon (O-C) shell mergers, a process proposed for the Cas A progenitor. We investigate this pre-supernova contribution by combining NuSTAR measurements of the spatial and kinematic distribution of ^44Ti with X-ray and infrared ejecta diagnostics. The low- and intermediate-velocity ^44Ti components are more closely associated with O-layer tracers than with shocked Fe-rich material. If the ^44Ti associated with the O-layer tracers was synthesized prior to core collapse, it could contribute up to ∼7×10^−5 M_⊙, about half of the total. We find that this amount of ^44Ti can be produced in O-C shell-merger models with ingestion rates and convective velocities higher than those in standard one-dimensional stellar-evolution calculations. Stable Fe-group abundance ratios measured with XRISM provide an additional constraint on the explosive contribution, as three-dimensional models with larger ^44Ti yields tend to predict Ti/Fe and Mn/Cr ratios above the observed values. These results suggest that both pre-supernova shell-merger nucleosynthesis and explosive burning contribute to the observed ^44Ti.
ER -