  The enhanced activity typical of the core of Seyfert galaxies can drive
powerful winds where high-energy phenomena can occur. In spite of their high
power content, the number of such non-jetted active galactic nuclei (AGN)
detected in gamma rays is very limited. In this Letter, we report the
identification and measurement of the gamma-ray flux from NGC 4151, a Seyfert
galaxy located at about 15.8 Mpc. The source is known for hosting ultra-fast
outflows (UFOs) in its innermost core through X-ray spectroscopic observations,
thereby becoming the first UFO host ever recognized in gamma rays. UFOs are
mildly relativistic, wide opening angle winds detected in the innermost parsecs
of active galaxies where strong shocks can develop. We interpret the gamma-ray
flux as a result of diffusive shock acceleration at the wind termination shock
of the UFO and inelastic hadronic collisions in its environment. Interestingly,
NGC 4151 is also spatially coincident with a weak excess of neutrino events
identified by the IceCube neutrino observatory. We compute the contribution of
the UFO to such a neutrino excess and we discuss other possible emission
regions such as the AGN corona.
