Heavy Element Nucleosynthesis in Rotating Protomagnetar Winds

Abstract The astrophysical origin of elements synthesized through the rapid neutron capture process ( r- process) is a long-standing mystery. The hot and dense environments of core-collapse supernovae have been suggested as potential r- process sites, particularly the neutrino-driven wind from the newly born protoneutron star (PNS). Wind models that neglect the potential effects of strong magnetic fields and/or rapid rotation of the PNS typically fail to achieve the necessary conditions for production of the third r- process peak, but robustly produce a limited or weak r- process for neutron-rich winds. Axisymmetric magnetohydrodynamic simulations of rotating and nonrotating PNS winds with magnetar-strength fields reveal that high entropy material is quasiperiodically ejected from the equatorial closed zone of the PNS magnetosphere. Here, we postprocess tracer particle trajectories from these simulations using a nuclear reaction network in order to explore the resulting nucleosynthesis across a range of PNS magnetic field strengths, rotation rates, and neutrino luminosities (cooling phase after core-bounce). We find that a robust r- process up to and beyond the third peak is generic to magnetar birth, even for magnetic fields as weak as ∼5 × 10 14 G. Depending on the distribution of magnetic field strengths and rotation at birth, we estimate that magnetized PNS winds could account for ∼5%–100% of the Galactic r- process inventory, extending up to the third peak. The robust r- process in our calculations is accompanied by overproduction of elements with mass number A ≲ 120 compared to the solar abundances. We also find that 92 Mo (a p- isotope) is produced in significant quantities in neutron-rich winds.