Investigating the polar spectra in IBEX's global ENA sky maps

The Interstellar Boundary Explorer (IBEX) mission has produced close to six global energetic neutral atom (ENA) sky maps of the heliospheric interface since its launch in October 2008. Spectral analysis of these maps revealed a strong latitudinal dependence of ENA spectra. Ulysses measurements have revealed a similarly structured latitudinal dependence of solar wind bulk speed. The polar regions, in particular, are characterized by a unique spectral shape, a strong flattening between ~1 keV and ~2 keV. It is believed to be caused by the fast solar wind at high latitudes, which generates and entrains a substantially higher-energy pickup ion component compared to the ecliptic. Using five IBEX-Hi ENA maps each constructed over a six-month period at 5 different energies between ~0.5 and ~6 keV, we investigate the possible ion sources inside the heliosphere that could contribute to the observed polar ENA spectra such as the fast solar wind, interstellar pick-up ions, and the suprathermal tail. We also study the long-term (6 months) variations of ENA fluxes, energy spectral shapes, and the energy dependence of the spectral indices in the polar regions and their correlation with the solar wind parameters observed at 1 AU.