Heliospheric energetic hydrogen atoms as a source of interplanetary energetic protons

Abstract

Heliospheric energetic hydrogen atoms below 100 keV have been detected at 1 AU with a strong anisotropy toward the heliotail by the instrument CELIAS on SOHO (1). These energetic neutrals are seen as results of anomalous cosmic-ray (ACR) protons transcharging with the local interstellar medium (LISM) in the outer heliosphere. The resulting neutrals then travel on ballistic trajectories, unaffected by the interplanetary magnetic field (IMF), to the inner heliosphere. In the vicinity of the sun, a fraction of these energetic neutrals are ionized again by photoionisation or collision with the solar wind protons and electrons. These energetic protons will then travel along the IMF and contribute to the quiet-time interplanetary energetic proton flux in the energy range below about 100 keV. This contribution should be proportional to the integrated energetic hydrogen atom flux in the heliosphere and therefore the production of energetic neutral hydrogen at the edge of the heliosphere. We estimate the flux uppe...