Scrutinizing FR 0 Radio Galaxies as Ultra-High-Energy Cosmic Ray Source Candidates

Abstract

Fanaroff-Riley (FR) 0 radio galaxies compose a new class of radio galaxies, which are usually weaker but much more numerous than the well-established class of FR 1 and FR 2 galaxies. The latter classes have been proposed as sources of the ultra-high-energy cosmic rays (UHECRs) with energies reaching up to $\sim 10^{20}$ eV. Based on this conjecture, the possibility of UHECR acceleration and survival in an FR 0 source environment is examined in this work. In doing so, an average spectral energy distribution (SED) based on data from the FR 0 catalog (FR0CAT) is compiled. The resulting photon fields are used as targets for UHECRs, which suffer from electromagnetic pair production, photo-disintegration, photo-meson production losses, and synchrotron radiation. Multiple mechanisms are discussed to assess the UHECR acceleration probability, including Fermi-I order and gradual shear accelerations, and particle escape from the source region. This work shows that in a hybrid scenario, combining Fermi and shear accelerations, FR 0 galaxies can contribute to the observed UHECR flux, as long as ${\Gamma }_{\mathrm{j}}\gtrsim 1.6$, where shear acceleration starts to dominate over escape. Even in less optimistic scenarios, FR 0s can be expected to contribute to the cosmic-ray flux between the knee and the ankle. Our results are relatively robust with respect to the realized magnetic turbulence model and the speed of the accelerating shocks.

19 pages, 16 figures, 4 tables, accepted in Astroparticle Physics

References in corpus (15)

• The NumPy array: a structure for efficient numerical computation
• The Co-Evolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe
• Observation of a Large-scale Anisotropy in the Arrival Directions of Cosmic Rays above $8\times 10^{18}$ eV
• Energy spectra of gamma-rays, electrons and neutrinos produced at interactions of relativistic protons with low energy radiation
• Measuring the kinetic power of AGN in the radio mode
• Fermi acceleration in astrophysical jets
• Ultra High Energy Cosmic Rays from Black Hole Jets of Radio Galaxies
• FR0CAT: a FIRST catalog of FR0 radio galaxies
• A microscopic analysis of shear acceleration
• Power requirements for cosmic ray propagation models involving diffusive reacceleration; estimates and implications for the damping of interstellar turbulence
• Particle Acceleration in Shearing Flows: Efficiencies and Limits
• Absorption of Nuclear Gamma-rays on the Starlight Radiation in FR I Sources: the Case of Centaurus A
• On the non-thermal electron-to-proton ratio at cosmic acceleration sites
• The large-scale environment of FR 0 radio galaxies
• On the radiation energy density in the jet of high-energy emitting BL Lac objects and its impact on their multi-messenger role

Cited by in corpus (8)

• Active Galactic Nuclei as potential Sources of Ultra-High Energy Cosmic Rays
• Anisotropic cosmic-ray diffusion in isotropic Kolmogorov turbulence
• On the sub-parsec scale core composition of FR 0 radio galaxies
• Efficient Modeling of Heavy Cosmic Rays Propagation in Evolving Astrophysical Environments
• The UHECR-FR0 Radio Galaxy Connection: A Multi-Messenger Study of Energy Spectra/Composition Emission and Intergalactic Magnetic Field Propagation
• Spine-sheath jet model for low-luminosity AGNs
• Particle Acceleration in Relativistic Shearing Flows: Energy Spectrum
• A New Gamma-ray Emitting Population of FR0 Radio Galaxies