COSMIC RAYS FROM ACCRETING ISOLATED NEUTRON STARS

Abstract

Interstellar matter that is accreted onto isolated magnetic neutron stars in the Galaxy ($\sim 10^9$ by number) is accelerated and reflected back by MHD shocks, which envelope the stars. The integrated power in the Galaxy $L_{cr,ns}$ is $ \sgreat 10^{40} {\rm erg \ s^{-1} }$, the energy distribution is a power law of spectral index $> 2$, and the particle energy can be raised to $10^6$ GeV, consistent with the power and spectrum of primary cosmic rays in the Galaxy. The major contribution for $L_{cr,ns}$ comes from a minority of $\sim 10^7$ isolated neutron stars which are located within dense clouds. Sources in these clouds, that are generally spread within the Galactic disk, 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.