Ultra-high-energy cosmic rays by Cygnus A or the bulk of non-local radio galaxies?
August 01, 2019
The great potential that radio galaxies are the birthplace of ultra-high-energy cosmic rays (UHECRs) has been shown by numerous works so far.
In addition to the close-by Fanaroff and Riley (FR) radio galaxy Centaurus A that most likely provides the dominant UHECR contribution at the highest energies, there is an other contributor between 5 EeV and 30 EeV needed.
The exceptionally bright radio source Cygnus A is a prominent source candidate, but it is shown in this work, that the impact by the extragalactic magnetic field on the CR propagation causes some serious issues: Either the arrival directions of the CRs provide a high degree of anisotropy or the delay exceeds the source age.
Alternatively, the low-energetic UHECRs can originate in the bulk of FR-I or FR-II sources. For such a scenario, the necessary jet dynamics of FR sources are discussed, showing that FR-I RGs can in principle provide the observed amount of UHECR energy as well as a proper spectral behavior. In contrast, the bulk of FR-II RGs most likely contribute less than 25%.
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