Spectral analysis of the heliospheric ENA emissions using Cassini/INCA measurements

Details Spectral analysis of the heliospheric ENA emissions using Cassini/INCA measurements Spectral analysis of the heliospheric ENA emissions using Cassini/INCA measurements

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh11a1904d&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SH11A-1904

Physics

[2124] Interplanetary Physics / Heliopause And Solar Wind Termination, [2126] Interplanetary Physics / Heliosphere/Interstellar Medium Interactions, [2151] Interplanetary Physics / Neutral Particles

Scientific paper

Understanding the changeable cause of a striking heliospheric signature such as the "Belt", discovered by the use of Energetic Neutral Atom (ENA) measurements, which was not predicted in the past by any theoretical model, would require time and energy-dependent analyses of the ENA emissions. All-sky energy-resolved ENA maps obtained by the INCA instrument onboard Cassini over the time period 2003 to 2009, in 4 discrete energy passbands (~ 5.4 to ~ 55 keV), are used to investigate the geometrical characteristics of the Belt, while spectral analyses are performed to further examine its possible energy dependence and possible variability with time. The resulting maps revealed that the ENA emissions forming the Belt are moderately well organized in galactic coordinates, i.e., they fall roughly within ±60° latitude about the galactic equator, although the maps in ecliptic coordinates are not inconsistent with a more efficient termination-shock acceleration at higher latitudes. By integrating each map over ~11.25° in galactic longitude and ~9° in latitude we are able to examine the degree of this organization by producing galactic latitude profiles and the corresponding energy spectra (in both Galactic and Ecliptic coordinates) of the ENA emissions throughout the sky sphere. Primary results of this study are summarized as follows: (a) statistically significant variations are found in the latitudinal profiles in all energy ranges and longitudes, with several relative peaks across the Belt; (b) the Belt extends to a latitudinal width of ~60-80° Full Width at Half Maximum (FWHM) in a longitudinal range of 180° to 60°, it then widens to ~100° in the range of 0° to -90° longitude and narrows to ~50° FWHM as it loops back to wrap around the sky sphere, (c) the consistency of the ENA distributions as a function of galactic latitude among the different INCA channels indicates that the morphology of the Belt (peak, width and structure) is almost energy-independent from 5 keV to 35 keV (minor deviations start to appear from >35 keV energies). (d) The ENA spectra show a power law form in energy and can be fitted with a single function presenting higher spectral slopes in the Belt region and lower outside (3.4<γ<4.4).

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