Effect of the Interstellar Magnetic Field Draping around the Heliopause on the IBEX Ribbon

Abstract

Abstract A dominant feature in all-sky maps of energetic neutral atoms (ENAs) from NASA’s Interstellar Boundary EXplorer (IBEX) is a ribbon of enhanced fluxes. This ribbon was not predicted before IBEX, but all the up-to-date IBEX observations support a secondary ENA mechanism for the ribbon formation. There are two different classes of the secondary ENA model; the first class assumes a weak pitch angle scattering of energetic protons in the local interstellar medium (LISM), and the second class assumes strong, but spatially localized, scattering. A recent work by Gamayunov et al. strongly supports a “weak scattering” version, and here we extend the scope of the Gamayunov et al. model by using a more realistic interstellar magnetic field (ISMF) from our global MHD-plasma/kinetic-neutral simulation of the heliosphere–LISM interaction in place of the simple analytical model used previously. The main conclusions of our analysis are summarized as follows. (1) Pitch angle scattering of energetic protons in the LISM is not the primary mechanism that controls the width of ribbon. Instead, the ribbon width is mainly determined by draping of the ISMF around the heliopause. (2) The intensity of the ribbon is controlled by pitch angle scattering of energetic protons in the LISM. A model–IBEX comparison suggests that generation of the small-scale local turbulence is suppressed in the LISM. On the other hand, the large-scale interstellar turbulence (LSIT) alone or an interplay between the LSIT and the case of no scattering leads to a good agreement between the model and IBEX fluxes.