Centaurus A as the source of ultrahigh-energy cosmic rays?
Résumé
We present numerical simulations for energy spectra and angular distributions of nucleons above 1019 eV injected by the radio-galaxy Centaurus A at a distance 3.4 Mpc and propagating in extra-galactic magnetic fields in the submicro Gauss range. We show that field strengths B~=0.3 μG, as proposed by Farrar and Piran, cannot provide sufficient angular deflection to explain the observational data. A magnetic field of intensity B~=1 μG could reproduce the observed large-scale isotropy and could marginally explain the observed energy spectrum. However, it would not readily account for the E=320+/-93 EeV Fly's Eye event that was detected at an angle 136° away from Cen-A, and it saturates observational upper bounds on the strength of extra-galactic magnetic fields. High energy cosmic ray experiments now under construction will be able to detect the level of anisotropy predicted by this scenario. We conclude that for magnetic fields B~=0.1-0.5 μG, considered as more reasonable for the local supercluster environment, in all likelihood at least a few sources within ~=10 Mpc from the Earth should contribute to the observed ultrahigh-energy cosmic ray flux.
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