The Production of Ultra High Energy Cosmic Rays during the Early Epochs of Radio-loud AGN

Abstract

Powerful radio-loud active galactic nuclei (AGN) with large Mpc-scale jets have been theoretically motivated as emitters of high-energy cosmic rays. Recent radio observations have established a populous class of young radio-loud galaxies with compact ($<1$ kpc) symmetric jets that are morphologically similar to large-scale AGNs. We show that these compact AGNs, so-called compact symmetric objects (CSOs), can accelerate protons up to $10^{20}$ eV at their hot spots via a Fermi type mechanism on the assumption of efficient acceleration. The required magnetic field strengths are comparable to those derived from the minimum energy condition. We further show that the accelerated protons can escape through the photon fields of the cocoon without significant energy loss. However, the local number density of powerful CSOs is insufficient for CSOs to power the entire observed flux of ultra-high-energy cosmic rays, providing maximally only a few percent. A heavy composition of UHECRs allows more CSOs to accelerate particles to UHECR energies, but escaping the cocoon is difficult. We comment on a method that may test CSOs as UHECR sources.

7 pages, 3 figures

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Cited by in corpus (5)

• Compact steep-spectrum and peaked-spectrum radio sources
• Bounds on the origin of extragalactic ultrahigh energy cosmic rays from the IceCube neutrino observations
• On the synthesis of heavy nuclei in protomagnetar outflows and implications for ultra-high energy cosmic rays
• Fossil shell in 3C 84 as TeV $\gamma$-ray emitter and cosmic-ray accelerator
• Constraints on Physical Conditions for the Acceleration on Ultra-high-energy Cosmic Rays in Nearby Active Galactic Nuclei Observed with the Fermi Large Area Telescope