Speaker
Description
Ultra-fast outflows (UFOs) of plasma from actively accreting galactic nuclei (AGN) are large-scale, mildly relativistic flows of highly ionised material. The interaction of these outflows with the interstellar medium can lead to the formation of collisionless shocks that are potential sites for the acceleration of elementary particles to ultra-high energies ("cosmic rays"). We study the cosmic-ray spectrum and maximum energy achievable in these UFOs via semi-analytical modelling and three-dimensional numerical simulations. We apply this approach to a sample of 86 observed UFOs and find that heavy nuclei, e.g. iron, can be accelerated up to $100\,$EeV at the wind-termination shock in some UFOs -- corresponding to the highest observed energies of cosmic rays at Earth. However, the escaping flux is attenuated strongly due to photonuclear interactions with the intense photon fields of the nearby AGN unless the cosmic rays are predominantly protons. We show that UFOs can provide an important contribution to the observed flux of ultra-high-energy cosmic rays. In addition, we predict a substantial flux of high-energy neutrinos from interactions of the accelerated cosmic rays in the UFOs.
