Pressure of the proton plasma in the inner heliosheath

G. Livadiotis, D. J. McComas, N. A. Schwadron, H. O. Funsten, S. A. Fuselier

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We develop a physical model to study the pressure of the source proton plasma in the inner heliosheath based on the IBEX Energetic Neutral Atom (ENA) spectra. A multiple linear regression technique is used to parameterize the proton distribution function, by connecting the observed ENA flux spectrum from IBEX-Hi with the power-law of the model proton distribution. We calculate the partial pressure over the measured energy range, using (1) a non-parametric method by integrating the observed ENA flux, and (2) a parametric method by integrating the modeled distribution of protons in the inner heliosheath. The two sky maps of the parametric and non-parametric partial pressures are nearly identical, owing to their power-law distributions at high energies; the kappa distribution is such a function that can be reduced to a power-law in the IBEX-Hi energy range. The slight differences between the two partial pressures may indicate protons that are not described by the kappa distribution, and instead, involve newer or "immature" (spherical shell) pick-up proton distributions. Ultimately, however, these become incorporated with the solar wind into one single proton population described by a kappa distribution. Moreover, we derive analytically (1) the ENA flux spectra, which suggests that this flux maximizes at ∼30 eV, and (2) the differential pressure, which provides estimates of the partial pressures outside of those measured by IBEX-Hi. Under the assumptions of the modeled ENA spectra, the Ribbon emissions appear to be primarily limited to the energy ranges of IBEX-Lo and IBEX-Hi.

Original languageEnglish (US)
Article number134
JournalAstrophysical Journal
Issue number2
StatePublished - Jan 10 2013
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • ISM: kinematics and dynamics
  • Interplanetary medium
  • Plasmas
  • Sun: heliosphere
  • methods: analytical
  • methods: statistical
  • solar wind


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