Spectral properties of regions and structures in the interstellar boundary explorer (IBEX) sky maps

We study the spectral properties of different regions and structures in the energetic neutral atom (ENA) maps at energies from ∼ 0.5keV to ∼ 6keV from the Interstellar Boundary Explorer (IBEX) mission. We find that (1) an ankle-shaped break (spectrum hardens) between 1keV and ∼ 2keV characterizes the polar spectra and the right flank, while a knee-shaped break (spectrum softens) describes the ribbon, nose, and the front region spectra; (2) the spectral indices across full latitudinal range (tail and poles) comprise a dependence reflecting a knee break at mid latitudes and an ankle break at high latitudes. This latitudinal evolution has inflection points at 40°S and 36°N, and is strongly correlated with the solar wind speed structure obtained by the Ulysses/SWOOPS instrument during its fast latitude scan in 2007. Our study confirms that the ecliptic latitude predominantly orders the spectral signatures of ENA distributions. This ordering may reflect the average solar wind properties that vary characteristically with latitude around solar minimum. We report on the spectral analyses of six regions and two structures in the IBEX maps. We also discuss the spectral asymmetries between the north and the south polar regions, their correlation with solar wind measurements, and the implications of these observations. Thus, we show detailed connections between the IBEX energy spectra and latitudinal properties of solar wind.