Profiles of the Ribbon: Systematic ENA Flux Features Within and Beyond the Central Ribbon

Herbert O Funsten, Los Alamos National Laboratory, ISR-DO, Los Alamos, NM, United States, Robert Demajistre, JHU/APL, Laurel, United States, Priscilla C Frisch, University of Chicago, Astronomy and Astrophysics, Chicago, IL, United States, Stephen A Fuselier, Southwest Research Institute, San Antonio, United States, Paul H Janzen, University of Montana, Missoula, MT, United States, George Livadiotis, Princeton University, Department of Astrophysical Sciences, Princeton, NJ, United States, David J McComas, Southwest Research Institute San Antonio, San Antonio, TX, United States, Kyle T Pittman, Los Alamos Natl Laboratory, Los Alamos, NM, United States, Daniel Brett Reisenfeld, Los Alamos National Laboratory, Los Alamos, NM, United States and Nathan Schwadron, Los Alamos National Laboratory, Los Alamos, United States
Abstract:
The ribbon of enhanced energetic neutral atom (ENA) flux is the most prominent feature of outer heliospheric ENA emission as observed by the Interstellar Boundary Explorer (IBEX). Here, we study the systematic variation of ENA flux in the ribbon and in its vicinity as a function of angle from the ribbon center at ecliptic (219°, 40°) as projected in the sky. We find that the ENA emission on the interior of the ribbon (between the ribbon and the ribbon center) is correlated with the emission brightness of the ribbon peak, whereas ENA emission on the exterior of the ribbon (between the ribbon and the antipode of the ribbon center) is not correlated with ribbon brightness. The ribbon flux falls to zero beyond a great circle in the sky at 90º from the ribbon center and is thus constrained to a hemisphere of emission that is centered on the ribbon center. These results are consistent with the “secondary” emission process of ribbon formation in the outer heliosheath [Heerikhuisen et al., 2010; McComas and Schwadron, 2013]. We additionally deconvolve the IBEX point spread function from analytical fits to the ribbon shape. We find that the ribbon peak is approximately 5% brighter than observations that do not consider the PSF. We also find a wide but consistent variation of ribbon widths, with the full width at half maximum ranging from 14º and 34º for 0.7-2.7 keV. At 4.3 keV the ribbon is consistently wider, with a 24º minimum ribbon width. We discuss the implications of the sharpness of the ribbon peak for observations of the Interstellar Mapping and Acceleration Probe (IMAP).
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