Structure and Dynamics of the IBEX Ribbon of Enhanced ENA Emission: The Role of ENA Transport in the Interstellar Medium

The bright energetic neutral atom (ENA) emission that forms the circular ribbon observed by the Interstellar Boundary Explorer (IBEX) reveals fundamental ordering of the underlying physical processes of the interaction of the heliosphere with the interstellar medium (ISM). Using 0.7-4.3 keV ENA flux maps from the IBEX-Hi ENA imager, we identify and quantify systematic features of the ribbon, including the minimum width of the ribbon after deconvolution of the IBEX point spread function, the characteristic radial profile of the ribbon flux that spans all energies and ribbon locaitons, and ENA flux observed toward the ribbon center that can be associated with the ribbon. We also investigate the "secondary ENA" ribbon hypothesis in which ENAs are emitted into the ISM, are ionized, and subsequently re-emitted as secondary ENAs, forming brighter emission from preferred geometrical locations (e.g., where the IBEX line-of-sight is perpendicular to the interstellar magnetic field). We track ENA transport into the ISM, their processing as ions in the ISM, and their re-emission as ENAs and return to the inner heliosphere. Additionally, the contribution to the ENA flux observed by IBEX from the apparent motion of the ISM as viewed from the Sun motion is quantified for the "secondary ENA" ribbon hypothesis and compared with direct ENA emission from sources located within the heliosphere and outside of the heliosphere.