The effects of a kappa-distribution in the heliosheath on the global heliosphere and ENA flux at 1 AU

TL;DR

This study models heliosheath proton distributions using a kappa-distribution to better understand ENA fluxes at 1 AU, revealing significant impacts on global heliosphere structure and ENA observations relevant to the IBEX mission.

Contribution

It introduces the use of a kappa-distribution for heliosheath protons in ENA flux modeling, improving interpretation of IBEX data and understanding of heliosphere-LISM interactions.

Findings

Kappa-distribution increases ENA fluxes above 1 keV.

Using kappa reduces differences between ENA maps at different energies.

Heliosphere boundary shifts: termination shock out by 4 AU, heliopause in by 9 AU, bow shock out by 25 AU.

Abstract

We investigate heliosheath energetic neutral atom (ENA) fluxes at keV energies, by assuming that the heliosheath proton distribution can be approximated by a kappa-distribution. The choice of the kappa parameter derives from observational data of the solar wind (SW). This has direct applications to the upcoming IBEX mission. We will look at all-sky ENA maps within the IBEX energy range (10 eV to 6 keV), as well as ENA energy spectra in several directions. We find that the use of kappa, as opposed to a Maxwellian, gives rise to greatly increased ENA fluxes above 1 keV, while medium energy fluxes are somewhat reduced. We show how IBEX data can be used to estimate the spectral slope in the heliosheath, and that the use of kappa reduces the differences between ENA maps at different energies. We also investigate the effect introducing a kappa-distribution has on the global interaction between the SW and the local interstellar medium (LISM), and find that there is generally an increase in energy transport from the heliosphere into the LISM, due to the modified profile of ENA's energies. This results in a termination shock that moves out by 4 AU, a heliopause that moves in by 9 AU and a bow shock 25 AU farther out, in the nose direction.