The energy-dependent position of the IBEX ribbon due to the solar wind structure

TL;DR

This study explains the energy-dependent position shift of the IBEX ribbon as a result of the solar wind's latitudinal structure, supporting its connection to the local interstellar magnetic field, but notes discrepancies at higher energies.

Contribution

The paper introduces an analytic model linking the ribbon's energy-dependent position shift to the solar wind structure, enhancing understanding of its origin and relation to interstellar magnetic fields.

Findings

The ribbon's geometric center shifts by about 10° across energies 0.7-4.3 keV.

Modeling supports the secondary ENA emission mechanism for the ribbon.

Observed center shifts at high energies exceed model predictions, indicating additional processes.

Abstract

Observations of energetic neutral atoms (ENAs) allow for remote studies of the plasma condition in the heliosphere and the neighboring local interstellar medium. The first IBEX results revealed an arc-like enhancement of the ENA intensity in the sky, known as the ribbon. The ribbon was not expected from the heliospheric models prior to the IBEX launch. One of the proposed explanations of the ribbon is the mechanism of the secondary ENA emission. The ribbon reveals energy-dependent structure in the relative intensity along its circumference and in the position. Namely, the ribbon geometric center varies systematically by about 10$^\circ$ in the energy range 0.7-4.3 keV. Here, we show by analytic modeling that this effect is a consequence of the helio-latitudinal structure of the solar wind reflected in the secondary ENAs. Along with a recently measured distance to the ribbon source just beyond the heliopause, our findings support the connection of the ribbon with the local interstellar magnetic field by the mechanism of the secondary ENA emission. However, the magnitude of the center shift in the highest IBEX energy channel is much larger in the observations than expected from the modeling. This may be due to another, not currently recognized, process of ENA generation.