Imaging the heliosphere using neutral atoms from solar wind energy down to 15 eV

Journal Article · Thu Nov 20 00:00:00 EST 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/796/1/9· OSTI ID:22370214

Galli, A.; Wurz, P. ^[1]; Fuselier, S. A.; McComas, D. J. ^[2]; Bzowski, M.; Sokół, J. M.; Kubiak, M. A. ^[3]; Möbius, E. ^[4]

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1. Physics Institute, University of Bern, Bern 3012 (Switzerland)
2. Southwest Research Institute, San Antonio, TX 78228 (United States)
3. Space Research Centre, Polish Academy of Sciences, Warsaw 00-716 (Poland)
4. University of New Hampshire, Durham, NH 03824 (United States)

We study the spatial and temporal distribution of hydrogen energetic neutral atoms (ENAs) from the heliosheath observed with the IBEX-Lo sensor of the Interstellar Boundary EXplorer (IBEX) from solar wind energies down to the lowest available energy (15 eV). All available IBEX-Lo data from 2009 January until 2013 June were included. The sky regions imaged when the spacecraft was outside of Earth's magnetosphere and when the Earth was moving toward the direction of observation offer a sufficient signal-to-noise ratio even at very low energies. We find that the ENA ribbon—a 20° wide region of high ENA intensities—is most prominent at solar wind energies whereas it fades at lower energies. The maximum emission in the ribbon is located near the poles for 2 keV and closer to the ecliptic plane for energies below 1 keV. This shift is an evidence that the ENA ribbon originates from the solar wind. Below 0.1 keV, the ribbon can no longer be identified against the globally distributed ENA signal. The ENA measurements in the downwind direction are affected by magnetospheric contamination below 0.5 keV, but a region of very low ENA intensities can be identified from 0.1 keV to 2 keV. The energy spectra of heliospheric ENAs follow a uniform power law down to 0.1 keV. Below this energy, they seem to become flatter, which is consistent with predictions. Due to the subtraction of local background, the ENA intensities measured with IBEX agree with the upper limit derived from Lyα observations.

• OSTI ID: 22370214
• Journal Information: Astrophysical Journal, Vol. 796, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ATOMS
DISTRIBUTION
EARTH MAGNETOSPHERE
EMISSION
ENERGY SPECTRA
EV RANGE
HELIOSPHERE
HYDROGEN
KEV RANGE
LYMAN LINES
PLASMA
SIGNAL-TO-NOISE RATIO
SOLAR WIND
SUN