Scatter-free pickup ions beyond the heliopause as a model for the Interstellar Boundary Explorer (IBEX) ribbon

TL;DR

This paper introduces a kinetic-gasdynamic model that explains the IBEX ribbon as resulting from scatter-free pickup ions beyond the heliopause, highlighting the role of secondary charge exchange and magnetic field configurations.

Contribution

The model incorporates scatter-free pickup protons and secondary charge exchange processes, advancing previous models to better explain the IBEX ribbon phenomenon.

Findings

Model reproduces the IBEX ribbon feature qualitatively.

Scatter-free pickup protons are a key source of ENAs at >1 keV.

Magnetic field conditions influence ribbon formation.

Abstract

We present new kinetic-gasdynamic model of the solar wind interaction with the local interstellar medium. The model incorporates several processes suggested by McComas et al. (2009) for the origin of the heliospheric ENA ribbon -- the most prominent feature seen in the all sky maps of heliospheric ENAs discovered by the Interstellar Boundary Explorer (IBEX). The ribbon is a region of enhanced fluxes of ENAs crossing almost the entire sky. Soon after the ribbon's discovery it was realized (McComas et al., 2009) that the enhancement of the fluxes could be in the directions where the radial component of the interstellar magnetic field around the heliopause is close to zero (Schwadron et al., 2009). Our model includes secondary charge exchange of the interstellar H atoms with the interstellar pickup protons outside the heliopause and is a further advancement of the kinetic-gasdynamic model by Malama et al. (2006) where pickup protons were treated as a separate kinetic component. Izmodenov et al. (2009) have shown in the frame of Malama's model that the interstellar pickup protons outside the heliopause maybe a significant source of ENAs at energies above 1 keV. The difference between the current work and that of Izmodenov et al. (2009) is in the assumption of no-scattering for newly created pickup protons outside the heliopause. In this limit the model produces a feature qualitatively similar to the ribbon observed by IBEX.