Neutrino-heated winds from rotating protomagnetars

Abstract

We calculate the steady-state properties of neutrino-driven winds from strongly magnetized, rotating proto-neutron stars (‘proto-magnetars’) under the assumption that the outflow ge-ometry is set by the force-free magnetic field of an aligned dipole. Our goal is to assess proto-magnetars as sites of r-process nucleosynthesis and gamma-ray burst engines. One di-mensional solutions calculated along flux tubes corresponding to different polar field lines are stitched together to determine the global properties of the flow at a given neutrino luminosity and rotation period. Proto-magnetars with rotation periods of P ∼ 2 − 5 ms are shown to produce outflows more favorable for the production of third-peak r-process nuclei due to their much shorter expansion times through the seed nucleus formation region, yet only moderately lower entropies, as compared to normal spherical PNS winds. Proto-magnetars with moder-ately rapid birth periods P ∼ 3 − 5 ms may thus represent a promising Galactic r-process site which is compatible with a variety of other observations, including the recent discovery of possible magnetar-powered supernovae in metal poor galaxies. We also confirm previous re-sults that the outflows from proto-magnetars with P ∼ 1−2 ms can achieve maximum Lorentz factors Γmax ∼ 100 − 1000 in the range necessary to power gamma-ray bursts (GRBs). The implications of GRB jets with a heavy nuclei-dominated composition as sources of ultra-high energy cosmic rays are also addressed. Key words: magnetars, neutrino-driven winds, r-process, gamma-ray bursts 1