Systematic exploration of heavy element nucleosynthesis in protomagnetar outflows

TL;DR

This study investigates nucleosynthesis in protomagnetar outflows, revealing their potential to produce intermediate/heavy mass ultra-high energy cosmic rays, with synthesis efficiency influenced by rotation speed and neutron richness.

Contribution

It systematically analyzes nucleosynthesis in protomagnetar winds using SkyNet, highlighting their capability to generate UHECRs and the impact of rotation and composition on element synthesis.

Findings

Heavy element synthesis occurs in the first 10 seconds for neutron-rich outflows.

Post-10 seconds, lighter elements dominate due to reduced photodisintegration.

Rapidly rotating protomagnetars favor nucleosynthesis, less dependent on magnetic field strength.

Abstract

We study the nucleosynthesis products in neutrino-driven winds from rapidly rotating, highly magnetised and misaligned protomagnetars using the nuclear reaction network SkyNet. We adopt a semi-analytic parametrized model for the protomagnetar and systematically study the capabilities of its neutrino-driven wind for synthesizing nuclei and eventually producing ultra-high energy cosmic rays (UHECRs). We find that for neutron-rich outflows ($Y_e<0.5$), synthesis of heavy elements ($\overline{A}\sim 20-65$) is possible during the first $\sim 10$ seconds of the outflow, but these nuclei are subjected to composition-altering photodisintegration during the epoch of particle acceleration at the dissipation radii. However, after the first $\sim 10$ seconds of the outflow, nucleosynthesis reaches lighter elements ($\overline{A}\sim 10-50$) that are not subjected to subsequent photodisintegration. For proton-rich ($Y_e \geq 0.5$) outflows, synthesis is more limited ($\overline{A}\sim 4-15$). These suggest that while protomagnetars typically do not synthesize nuclei heavier than second r-process peak elements, they are intriguing sources of intermediate/heavy mass UHECRs. For all configurations, the most rapidly rotating protomagnetars are more conducive for nucleosynthesis with a weaker dependence on the magnetic field strength.