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

Abstract

We investigated the possibility of acceleration of ultra-high-energy cosmic rays (UHECRs) in nearby active galactic nuclei (AGNs) using archival multi-wavelength observational data, and then we constrained their physical conditions, i.e., the luminosity of the synchrotron radiation and the size of the acceleration site. First, we investigated the spatial correlation between the arrival directions of UHECRs and the positions of nearby AGNs in the Fermi third gamma-ray source catalog. We selected 27 AGNs as candidates of accelerators of UHECRs. Then, we evaluated the physical conditions in the acceleration regions of these AGNs via the Pe'er and Loeb method, which uses the peak luminosity of synchrotron radiation and the peak flux ratio of inverse Compton scattering to synchrotron radiation. From the evaluation, we found that six AGNs have the ability to accelerate ultra-high-energy protons in the AGN cores. Furthermore, we found that the minimum acceleration size must be more than a few kpc for acceleration of UHE protons in the AGN lobes.

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