Jul 12 – 23, 2021
Europe/Berlin timezone

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

Jul 13, 2021, 12:00 PM
1h 30m


Talk MM | Multi-Messenger Discussion


Lukas Merten (University of Innsbruck)


Fanaroff Riley (FR) 0 radio galaxies form a low luminosity extension of the well established ultrahigh energy cosmic ray (UHECR) candidate accelerators FR-1 and FR-2 galaxies. Their much higher number density – up to a factor 5 more numerous compared to FR-1 with $z<= 0.05$ – makes them good candidate sources for an isotropic contribution to the observed UHECR flux. Here, 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 FR0CAT. These photon fields, composed of a jet and a host galaxy component, form a minimal target 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 gradual shear acceleration is preceded by an efficient acceleration mechanism, e.g., Fermi-I or others, FR-0 galaxies are likely UHECR accelerators. This scenario requires a jet Lorentz factor of $\gamma>1.6$ to yield gradual shear acceleration which is faster than the corresponding escape. In less optimistic models a contribution to the cosmic-ray flux between knee and ankle is expected relatively independent of the realized turbulence and acceleration.


acceleration of particles; radiation mechanisms: nonthermal;
galaxies: jets; galaxies: active; cosmic rays

Subcategory Theoretical Results

Primary authors

Lukas Merten (University of Innsbruck) Mrs Margot Boughelilba (University of Innsbruck) Anita Reimer (University of Innsbruck) Paolo Da Vela (University of Innsbruck) Serguei Vorobiov (University of Nova Gorica) Fabrizio Tavecchio (Astronomical Observatory of Brera) Giacomo Bonnoli (Instituto de Astrofisica de Andalucia) Jon Paul Lundquist (University of Nova Gorica) Chiara Righi (Astronomical Observatory of Brera)

Presentation materials