SEPARATION OF THE RIBBON FROM GLOBALLY DISTRIBUTED ENERGETIC NEUTRAL ATOM FLUX USING THE FIRST FIVE YEARS OF IBEX OBSERVATIONS

Abstract

The Interstellar Boundary Explorer (IBEX) observes the IBEX ribbon, which stretches across much of the sky observed in energetic neutral atoms (ENAs). The ribbon covers a narrow (∼20 •-50 •) region that is believed to be roughly perpendicular to the interstellar magnetic field. Superimposed on the IBEX ribbon is the globally distributed flux that is controlled by the processes and properties of the heliosheath. This is a second study that utilizes a previously developed technique to separate ENA emissions in the ribbon from the globally distributed flux. A transparency mask is applied over the ribbon and regions of high emissions. We then solve for the globally distributed flux using an interpolation scheme. Previously, ribbon separation techniques were applied to the first year of IBEX-Hi data at and above 0.71 keV. Here we extend the separation analysis down to 0.2 keV and to five years of IBEX data enabling first maps of the ribbon and the globally distributed flux across the full sky of ENA emissions. Our analysis shows the broadening of the ribbon peak at energies below 0.71 keV and demonstrates the apparent deformation of the ribbon in the nose and heliotail. We show global asymmetries of the heliosheath, including both deflection of the heliotail and differing widths of the lobes, in context of the direction, draping, and compression of the heliospheric magnetic field. We discuss implications of the ribbon maps for the wide array of concepts that attempt to explain the ribbon's origin. Thus, we present the five-year separation of the IBEX ribbon from the globally distributed flux in preparation for a formal IBEX data release of ribbon and globally distributed flux maps to the heliophysics community.

Effects of solar wind speed on the secondary energetic neutral source of the Interstellar Boundary Explorer ribbon

“…Comparing to Fig. 2 of Schwadron et al (2014), for the case of slow SW the simulated ribbon flux overestimates the observed flux below 1.11 keV, but underestimates above 1.11 keV. For the case of intermediate speed SW, we see the simulated ribbon flux is overestimated at 1.74 keV and 2.73 keV, produces results similar to observation at 1.11 keV, and is underestimated at the lowest and highest energies.…”

“…This can be seen by comparing to the separated IBEX ribbon flux in Fig. 2 of Schwadron et al (2014), which show a clear dimming of ribbon flux at low latitudes above ∼2 keV, relative to the high-latitude flux. Initial comparisons between the results and IBEX data suggest (1) SW with speeds between slow (∼400 km s −1 ) and intermediate (∼600 km s −1 ) must exist at low to mid latitudes to reproduce the ribbon at most energies; (2) the 2.73 keV ribbon shows that most of the SW below +30…”

“…1. The color bar scales are the same as those used by Schwadron et al (2014) in their separated ribbon results.…”

LATITUDINAL AND ENERGY DEPENDENCE OF ENERGETIC NEUTRAL ATOM SPECTRAL INDICES MEASURED BY THEINTERSTELLAR BOUNDARY EXPLORER

“…In this paper, we extend the work of Dayeh et al (2011Dayeh et al ( , 2012 and Schwadron et al (2014) by combining all-sky maps from only the first 3 yrs of IBEX-Hi ENA observations to understand in detail and quantify the latitudinal, longitudinal, and energy dependence of the 0.5-6 keV IBEX-Hi ENA spectral indices in the GDF. Using data from the first 3 yrs only allows us to minimize the effects of temporal variations that are clearly evident in the ENA fluxes and spectra (McComas et al 2014).…”

“…They also found a strong correlation between the latitudinal ordering of the ENA spectral slopes and breaks and that of the latitudinal profile of the SW speed observed in the inner heliosphere in 2007 (see e.g., Funsten et al 2009b;Dayeh et al 2011;Livadiotis et al 2011). More recently, Schwadron et al (2014) combined 5 yrs of IBEX-Hi and IBEXLo data to derive a single power-law spectral index over ∼0.2-6 keV in each pixel. The 5 yr spectral map of the globally distributed ENAs over this broad energy range has qualitatively confirmed the previously reported latitudinal dependence.…”