Speaker
Description
Magnetar giant flares are the most powerful non-cataclysmic neutron star outbursts, capable of releasing more than 1e46 ergs of magnetic energy within a fraction of a second. In recent work, we showed that giant flares can eject neutron-rich material from the magnetar crust and that radioactive decay in this ejecta produces delayed MeV gamma-ray emission consistent with a previously unexplained observation. This provides strong evidence that magnetar giant flares are a site of rapid neutron-capture process (r-process) nucleosynthesis. Motivated by this result and by the sub-second duration of the prompt gamma-ray spike of a giant flare, we consider a scenario in which magnetic energy dissipation injects energy near the magnetar surface over a few hundred milliseconds. This energy deposition ablates material from the neutron star surface and launches relativistic outflows. We will present our ongoing work based on two-dimensional relativistic hydrodynamic simulations. The simulations naturally produce a two-component structure: a fast, baryon-poor outflow directly above the energy injection region, capable of powering the prompt gamma-ray spike, and a slower, baryon-rich outflow in a surrounding conical region. Assuming steady-state conditions, we extract particle trajectories from the simulations and post-process them with a nuclear reaction network. We find that r-process nucleosynthesis produces material across all three r-process abundance peaks. Finally, adopting a simple phenomenological model for the energetics and occurrence rates of magnetar giant flares, we estimate their integrated contribution to Galactic r-process production. While uncertainties remain, our results suggest that magnetar giant flares are a robust secondary r-process site and provide a framework for improved modeling of the associated electromagnetic transients. The talk will emphasize open questions to encourage discussion and feedback.