Gamma-ray emission from the Seyfert galaxy NGC 4151: Multi-messenger implications for ultra-fast outflows

TL;DR

This paper investigates gamma-ray and neutrino emissions from the Seyfert galaxy NGC 4151, proposing that ultra-fast outflows can produce observable high-energy signals, with implications for multi-messenger astrophysics.

Contribution

It demonstrates that particle acceleration at UFO wind termination shocks can explain gamma-ray observations and links NGC 4151 to neutrino excesses, highlighting UFOs as high-energy sources.

Findings

NGC 4151's gamma-ray emission can be explained by UFO wind shocks.

NGC 4151 is spatially coincident with IceCube neutrino excess.

The gamma-ray source is likely not dominated by the nearby blazar.

Abstract

The nuclear activity typical of Seyfert galaxies can drive powerful winds where high-energy phenomena 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. 4FGL J1210.3+ 3928, a source recently discovered by the Fermi-LAT telescope, is spatially consistent with the blazar 1E 1217.9+3945 and NGC 4151, a Seyfert galaxy located at about 15.8 Mpc known for hosting ultra-fast outflows (UFOs) in its innermost core. We show that the localization of 4FGL J1210.3+3928 might be affected by fluctuations due to a superposition of the two nearby sources. We explore the possibility of NGC 4151 to be a high-energy source and we conclude that particle acceleration at the UFO wind termination shock can explain the luminosity and spectral shape of the observed gamma-ray flux, whereas the multiwavelength spectral energy distribution of 1E 1217.9+3945 disfavors it as the dominant GeV gamma-ray counterpart. 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 nearest neighborhood.