Remote diagnostic of the heliospheric termination shock using neutralized post shock pick-up ions as messengers

Hydrogen pick-up ions when produced in the inner heliosphere are convected outwards with the solar wind and are accelerated by nonlinear wave-particle interactions. Upon their arrival at the solar wind termination shock the highest percentage of them passes over from the preshock to the postshock plasma regime. At this occasion these ions suffer a characteristic change in their density and velocity distribution which sensitively reflects the shock properties. We calculate the postshock pick-up ion spectrum and demonstrate the influence of the density compression factor realized at the shock. We then calculate the distribution function of keV–Energetic Neutral H-Atoms (HENAs) originating as products of these postshock pick-up ions decharged by local H–atoms and show how, by detection of spectral H-ENA fluxes at the earth’s orbit, a very efficient remote diagnostic of the shock properties, especially the shock compression ratio, is enabled. ENAs up to energies of 5 keV clearly reflect the preshock plasma conditions, those at energies larger than 10 keV the postshock plasma conditions. In the energy range between 5 through 50 keV decharged H+ pick-up ions strongly dominate over all competing ENA fluxes which were discussed in the literature up to now.