First comparison of composite 0.52-55 keV ENA spectra observed by IBEX and Cassini/INCA with simulated ENAs inferred by proton hybrid simulations downstream of the termination shock

TL;DR

This study compares ENA measurements from IBEX and Cassini with hybrid simulation models to understand particle acceleration at the termination shock, revealing energy-dependent discrepancies in observed and simulated fluxes.

Contribution

It provides the first direct comparison of ENA spectra from two missions with hybrid simulation models, enhancing understanding of heliosheath particle acceleration.

Findings

Observed ENA fluxes are higher than simulated ones across energies.

Discrepancies are energy-dependent, indicating model or measurement limitations.

Results suggest the need for refined models of particle acceleration at the termination shock.

Abstract

We present a first comparison of Energetic Neutral Atom (ENA) heliosheath measurements, remotely sensed by the Interstellar Boundary Explorer (IBEX) mission and the Ion and Neutral Camera (INCA) on the Cassini mission, with modeled ENA inferred from interstellar pickup protons that have been accelerated at the termination shock, using hybrid simulations. The observed ENA intensities are an average value over the time period from 2009 to the end of 2012, along the Voyager 2 trajectory. The hybrid simulations parameters for the solar wind, interstellar pickup ions (PUIs), and magnetic field upstream of the termination shock, where Voyager 2 crossed, are based on observations. We report an energy dependent discrepancy between observed and simulated ENA fluxes, with the observed ENA fluxes, being consistently higher than the simulated ones, and discuss possible causes of this discrepancy.