Trends in 44Ti and 56Ni from Core-collapse Supernovae

We compare the yields of 44Ti and 56Ni produced from post-processing the thermodynamic trajectories from three different core-collapse models—a Cassiopeia A progenitor, a double shock hypernova progenitor, and a rotating two-dimensional explosion—with the yields from exponential and power-law trajectories. The peak temperatures and densities achieved in these core-collapse models span several of the distinct nucleosynthesis regions we identify, resulting in different trends in the 44Ti and 56Ni yields for different mass elements. The 44Ti and 56Ni mass fraction profiles from the exponential and power-law profiles generally explain the tendencies of the post-processed yields, depending on which regions are traversed by the model. We find that integrated yields of 44Ti and 56Ni from the exponential and power-law trajectories are generally within a factor two or less of the post-process yields. We also analyze the influence of specific nuclear reactions on the 44Ti and 56Ni abundance evolution. Reactions that affect all yields globally are the 3α, p(e–, νe)n and . The rest of the reactions are ranked according to their degree of impact on the synthesis of 44Ti. The primary ones include 44Ti(α, p)47V, 40Ca(α, γ)44Ti, 45V(p, γ)46Cr, 40Ca(α, p)43Sc, 17F(α, p)20Ne, 21Na(α, p)24Mg, 41Sc(p, γ)42Ti, 43Sc(p, γ)44Ti, 44Ti(p, γ)45V, and 57Ni(p, γ)58Cu, along with numerous weak reactions. Our analysis suggests that not all 44Ti need to be produced in an α-rich freeze-out in core-collapse events, and that reaction rate equilibria in combination with timescale effects for the expansion profile may account for the paucity of 44Ti observed in supernova remnants.