Production of ultra-high-energy γ-rays by accreting neutron stars

Several well-known binary X-ray sources have been reported to emit copious γ-radiation at energies up to and exceeding 10¹⁵ eV. It is proposed here that the observed events occur during episodes of non-steady accretion onto neutron stars, when MHD instabilities give rise to vortex motions onvery large scales deep inside the magnetosphere. The magnetic lines of force are strongly distorted and reconnect in neutral sheets, along which extremely high voltage drops are maintained and a small fraction of the particles are accelerated to ultra-relativistic energies. The γ-rays are produced in nuclear collisions undergone by runaway ions traversing regions of high-density, diamagnetic plasma in the accretion flow.