The non-jetted activity of active galactic nuclei (AGN) can result in mildly relativistic and wide opening angle outflows known as ultra-fast outflows (UFOs). UFOs, similar to stellar winds, can develop a bubble structure characterized by an inner wind termination shock and an outer forward shock. During the bubble lifetime, while the forward shock rapidly loses its efficiency in accelerating particles, ideal conditions for stationary acceleration at the wind termination shock can be achieved.
We present a model for diffusive shock acceleration at the wind termination shock of UFOs which predicts maximum proton energies extending up to the EeV range.
In addition, before escaping the UFO, a sizable fraction of accelerated particles is likely to interact with the highly dense gas and the strong radiation field typical of AGN.
We compute the gamma-ray and high-energy neutrino fluxes produced in such inelastic collisions together with the associated escaping flux.
We finally discuss the multi-messenger implications of our model in terms of cosmic rays, neutrino and gamma-rays produced in isolated UFOs as well as their cumulative diffuse emission.