Rapid stochastic acceleration of protons to energies above 100 TeV in the accretion column of Hercules X-1

Abstract An investigation into the acceleration of protons by scattering off relativistic Alfven waves in the accretion column of Hercules X-1 is presented. The mechanism is shown to achieve mean particle energies of 30 TeV under very reasonable assumptions about the environment, and 250 TeV is available under some circumstances. The highest individual energy attained is almost 1 PeV. The protons emerge in the form of a narrow beam directed at the inner edge of the accretion disk, which is favourable because of the reduced power requirement and presence of target material for γ-ray production.