Cosmic rays from accreting isolated neutron stars

Abstract

Interstellar matter that is accreted onto isolated magnetic neutron stars in the Galaxy ( ~ 109 by number) is accelerated and reflected back by (MHD) shocks, which envelope the stars. The integrated power in the Galaxy, Lcr,ns, is ≳ 1040 erg s–1, the energy distribution is a power law of spectral index > 2, and the particle energy can be raised to 106 GeV, consistent with the power and spectrum of primary cosmic rays in the Galaxy. The major contribution to Lcr,ns comes from a minority of ~ 107 isolated neutron stars which are located within dense clouds. Sources in these clouds, that are generally spread within the Galactic disc, can explain the concentration of high-energy cosmic rays in the Galactic plane, as deduced from pion decay spectra in gamma-ray observations. The soft X-ray luminosity from these neutron stars is consistent with the Galactic X-ray background. The accretion may be associated with ion-neutral bias, that is further enhanced by ion confinement in frozen-in magnetic fields, which can raise the relative abundance of first ionization potential (FIP) elements in the cosmic rays.