CONSTRAINTS ON THE PRODUCTION OF ULTRA-HIGH-ENERGY COSMIC-RAYS BY ISOLATED NEUTRON-STARS

The energetics, spectrum, and composition of cosmic rays with energies below similar to 10(15) eV are fairly well explained by models involv ing supernova shocks. In contrast, no widely accepted theory exists fo r the origin of ultra-high-energy cosmic rays (UHECRs), which have ene rgies above 10(15) eV. Instead of proposing a specific model, here we place strong constraints on any model of UHECRs involving isolated neu tron stars (no companions). We consider the total power requirements a nd show that the only viable power source associated with isolated neu tron stars is rotation. Mechanisms based on accretion from the interst ellar medium fall short of the necessary power despite the most optimi stic assumptions. Power considerations also demonstrate that not enoug h rotational energy is tapped by a ''propeller'' - like acceleration o f interstellar matter. The most promising source of energy is rotation al spindown via magnetic braking. We examine microphysical energy loss processes near magnetized neutron stars and conclude that the most li kely site for yielding UHECRs from isolated neutron stars is near or b eyond the light cylinder.