FR-0 jetted active galaxies: extending the zoo of candidate sites for UHECR acceleration

Lukas Merten; Margot Boughelilba; Anita Reimer; Paolo Da Vela; Serguei Vorobiov; Fabrizio Tavecchio; Giacomo Bonnoli; Jon Paul Lundquist; Chiara Righi

arXiv · 2107.13278

FR-0 jetted active galaxies: extending the zoo of candidate sites for UHECR acceleration

Lukas Merten·Margot Boughelilba·Anita Reimer·Paolo Da Vela·Serguei Vorobiov·Fabrizio Tavecchio·Giacomo Bonnoli·Jon Paul Lundquist·Chiara Righi

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Abstract

Fanaroff-Riley (FR) 0 radio galaxies form a low-luminosity extension to the well-established ultra-high-energy cosmic-ray (UHECR) candidate accelerators FR-1 and FR-2 galaxies. Their much higher number density -- up to a factor five times more numerous than FR-1 with $z\leq 0.05$ -- makes them good candidate sources for an isotropic contribution to the observed UHECR flux. Here, the acceleration and survival of UHECR in prevailing conditions of the FR-0 environment are discussed. First, an average spectral energy distribution (SED) is compiled based on the \textit{FR0CAT}. These photon fields, composed of a jet and a host galaxy component, form a minimal target photon field for the UHECR, which will suffer from electromagnetic pair production, photo-disintegration, photo-meson production losses, and synchrotron radiation. The two most promising acceleration scenarios based on Fermi-I order and gradual shear acceleration are discussed as well as different escape scenarios. When an efficient acceleration mechanism precedes gradual shear acceleration, e.g., Fermi-I or others, FR-0 galaxies are likely UHECR accelerators. Gradual shear acceleration requires a jet Lorentz factor of $\Gamma>1.6$, to be faster than the corresponding escape. In less optimistic models, a contribution to the cosmic-ray flux between the knee and ankle is expected to be relatively independent of the realized turbulence and acceleration.

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Lukas Merten, Margot Boughelilba, Anita Reimer, Paolo Da Vela, Serguei Vorobiov, Fabrizio Tavecchio, Giacomo Bonnoli, Jon Paul Lundquist, Chiara Righi. 2021-07-28. FR-0 jetted active galaxies: extending the zoo of candidate sites for UHECR acceleration. https://arxiv.org/abs/2107.13278

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