Contribution of nuclei accelerated by gamma-ray pulsars to cosmic rays in the Galaxy

Abstract

We consider the galactic population of gamma-ray pulsars as possible sources of cosmic rays at and just above the ``knee'' in the observed cosmic ray spectrum at $10^{15}$--$10^{16}$ eV. We suggest that iron nuclei may be accelerated in the outer gaps of pulsars, and then suffer partial photo-disintegration in the non-thermal radiation fields of the outer gaps. As a result, protons, neutrons, and surviving heavier nuclei are injected into the expanding supernova remnant. We compute the spectra of nuclei escaping from supernova remnants into the interstellar medium, taking into account the observed population of radio pulsars. Our calculations, which include a realistic model for acceleration and propagation of nuclei in pulsar magnetospheres and supernova remnants, predict that heavy nuclei accelerated directly by gamma-ray pulsars could contribute about 20% of the observed cosmic rays in the knee region. Such a contribution of heavy nuclei to the cosmic ray spectrum at the knee can significantly increase the average value of $<\ln A>$ with increasing energy as is suggested by recent observations.