Heliospheric X-ray Emission Associated with Charge Transfer of the Solar Wind with Interstellar Neutrals

Abstract

X-rays should be generated throughout the heliosphere as a consequence of charge transfer collisions between heavy (Z>2) solar wind ions and interstellar neutrals. The high charge state solar wind ions resulting from these collisions are left in highly excited states and emit extreme ultraviolet or soft X-ray photons. This solar wind charge exchange mechanism applied to cometary neutrals has been used to explain the soft X-ray emission observed from comets. A simple model demonstrates that heliospheric X-ray emission can account for about 25%-50% of the observed soft X-ray background intensities. The spatial and temporal variations of heliospheric X-ray emission should reflect variations in the solar wind flux and composition as well as variations in the distribution of interstellar neutrals within the heliosphere. The heliospheric X-ray "background" can perhaps be identified with the "long-term enhancements" in the soft X-ray background measured by ROSAT.