Spherical Harmonic Representation of Energetic Neutral Atom Flux Components Observed by IBEX

The Interstellar Boundary Explorer (IBEX) images the heliosphere by observing energetic neutral atoms (ENAs). The IBEX-Hi instrument on board IBEX provides full-sky maps of ENA fluxes produced in the heliosphere and very local interstellar medium through charge exchange of suprathermal ions with int...

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Bibliographic Details
Published in:The Astrophysical journal. Supplement series 2023-06, Vol.266 (2), p.26
Main Authors: Swaczyna, P., Dayeh, M. A., Zirnstein, E. J.
Format: Article
Language:English
Subjects:
Astronomical maps
Charge exchange
Energetic neutral atoms
Fluctuations
Heliopause
Heliosheath
Heliosphere
Interstellar magnetic fields
Interstellar medium
Interstellar medium wind
Local interstellar medium
Magnetic fields
Neutral atoms
Qualitative analysis
Representations
Solar cycle
Solar wind
Space plasmas
Spherical harmonics
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Summary:The Interstellar Boundary Explorer (IBEX) images the heliosphere by observing energetic neutral atoms (ENAs). The IBEX-Hi instrument on board IBEX provides full-sky maps of ENA fluxes produced in the heliosphere and very local interstellar medium through charge exchange of suprathermal ions with interstellar neutral atoms. The first IBEX-Hi results showed that, in addition to the anticipated globally distributed flux (GDF), a narrow and bright emission from a circular region in the sky, dubbed the IBEX ribbon, is visible in all energy steps. While the GDF is mainly produced in the inner heliosheath, ample evidence indicates that the ribbon forms outside the heliopause in the regions where the interstellar magnetic field is perpendicular to the lines of sight. The IBEX maps produced by the mission team distribute the observations into 6° × 6° rectangle pixels in ecliptic coordinates. The overlap of the GDF and ribbon components complicates qualitative analyses of each source. Here, we find the spherical harmonic representation of the IBEX maps, separating the GDF and ribbon components. This representation describes the ENA flux components in the sky without relying on any pixelization scheme. Using this separation, we discuss the temporal evolution of each component over the solar cycle. We find that the GDF is characterized by larger spatial scale structures than those of the ribbon. However, we identify two isolated, small-scale signals in the GDF region that require further study.
ISSN:0067-0049
1538-4365
DOI:10.3847/1538-4365/accf0f