Ultra-high energy cosmic rays and the strongest AGN flares

We perform an observational test of the hypothesis that ultra-high energy cosmic rays (E > 10²⁰ eV) are accelerated in giant flares of active galactic nuclei (AGN). We use the observations of Fermi LAT during the first 7.4 years of the mission. We select highly variable AGNs with the redshift z ≤ 0.3 and use an empirical relation between the bolometric luminosity and the jet kinetic power in order to find the local kinetic emissivity of strong AGN flares: L ∼ 1.1 * 10⁴⁵ erg Mpc^-3 yr^-1. This is approximately one order of magnitude larger than the UHECR emissivity estimated from the data of Pierre Auger and Telescope Array observatories which makes the whole scenario feasible provided the acceleration spectrum is sufficiently hard and/or narrow. (authors)