Very high-energy gamma rays from ultra-fast outflows

¹ LUX, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS, 92190 Meudon, France
² INAF, Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
³ APC, Université Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de Paris, Sorbonne Paris Cité, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 30 October 2025
Accepted: 8 March 2026

Abstract

Context. Ultra-fast outflows (UFOs) from active galactic nuclei (AGNs) are expected to lead to the formation of sub-relativistic strong shocks expanding in a dense, circumnuclear medium, and thus have the potential to be efficient particle accelerators and proficient sources of gamma rays and neutrinos.

Aims. We aim to investigate the detectability of a sample of nearby identified UFOs in gamma rays and neutrinos with current and next-generation instruments.

Methods. We modeled the acceleration of particles at the strong shocks of UFOs and estimated the associated gamma-ray and neutrino signal. We adopted our model to investigate the prospects for detection with current and next-generation observatories.

Results. We find that several UFOs could be detectable in the very-high-energy (VHE) domain – for example, by the Cherenkov Telescope Array Observatory (CTAO) – even if they remain undetected by Fermi-LAT in the high-energy range. Detectability is favored for hard proton spectra (spectral index α ≲ 3.9), high acceleration efficiencies, and amplified magnetic fields. Our results suggest that next-generation VHE observatories could detect the first gamma-ray signatures of AGN UFOs, providing a new probe of particle acceleration in sub-relativistic shocks.