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Abstract

Context. The shape of the ion energy spectra plays a critical role in determining the ion energetics, the acceleration mechanisms, and the possible sources of different plasma and suprathermal ion populations. The determination of the exact shape of the total particle spectrum provides the necessary means to address the inner heliosheath dynamics. Apart from various modelling efforts, a direct fit to the measured ion spectra for an extended energy range of ∼0.11-344 MeV has not been performed to date.
Aims: We use an extended set of combined 0.11-55 keV remotely sensed energetic neutral atoms (ENA) measurements from the Interstellar Boundary Explorer (IBEX-Lo and IBEX-Hi) and the Cassini/Ion and Neutral Camera (INCA), converted to protons, together with ∼28 keV-344 MeV in situ ion measurements from the low-energy charged particle (LECP) and cosmic ray subsystem (CRS) experiments on Voyager 2, over the declining phase of solar cycle 23 (SC23) and the ascending phase of solar cycle 24 (SC24) to study the characteristics of the particle energy spectrum.
Methods: We fitted the 0.11 keV-344 MeV composite ion spectra with a set of regularized isotropic κ-distribution functions (RKDs), which allowed us to determine the macroscopic physical properties.
Results: We demonstrate that the 2009-2012 composite spectrum that corresponds to the declining phase of SC23 is well fitted by three different RKDs, while the 2013-2016 spectrum, associated with the rise of SC24, can only be approximated with six different κ-distribution functions.
Conclusions: Our results are generally consistent with shock accelerated particles that undergo additional acceleration inside the inner heliosheath. We identify a low-energy transmitted population of particles, a suprathermal reflected population and a very-high-energy component that is modulated by galactic cosmic rays. The 2013-2016 time period is most likely associated with a mixture of particles from SC23 and SC24, which is reflected by the need to employ six RDKs.