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Titel |
Energetic Neutral Atom (ENA) Imaging of the Heliosheath: Spectral Characteristics and Implications for Shock Acceleration from Observations by the Neutral Particle Detector (NPD) on board Venus Express (VEX) |
VerfasserIn |
P. C. Brandt, E. C. Roelof, P. Wurz, S. Barabash, D. Bazell, R. DeMajistre, T. Sotirelis, R. Decker |
Konferenz |
EGU General Assembly 2009
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 11 (2009) |
Datensatznummer |
250027620
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Zusammenfassung |
Here we report on the spectral characteristics across the sky of ENAs in the ~0.1-3 keV range
generated in the heliosheath observed by NPD on board Venus Express. Plasma and energetic
particle measurements during the termination shock crossings by the Voyagers reveal that
most of the particle energization occurs in the pick-up ion energy range (~0.1-10 keV)
[Richardson, Nature, July, 2008] - a range that was not covered by the Voyager
instrumentation, but is covered by the ASPERA-4/NPD measurements. We seek to determine
if the ENA spectra observed by NPD are consistent with the expected energization at these
energies.
The Interstellar Boundary Explorer (IBEX) is the only mission so far dedicated to
imaging the heliosheath and was launched October 2008. While the IBEX data is currently
being analyzed, several other, non-dedicated instruments on board various missions (Venus
Express, Cassini, IMAGE, Mars Express, SOHO, STEREO) are seeking to provide
meaningful measurements of the structure and spectral characteristics of the heliosheath. One
of those instruments is the NPD belonging to the ASPERA-4 experiment suite on board
VEX. NPD is a time-of-flight (TOF) instrument using a coincidence technique to
identify ENAs (and is therefore not sensitive to, for example X-rays) and has an
instantaneous field-of-view (FOV) of 5-Ã180- with six sectors of each 5-Ã30- FOV.
A scanning platform allows the FOV to scan across half of the entire sky in one
scan.
By restricting about three years of measurements to Venus eclipse and to directions that
look more than 90- away from the Sun and Venus direction, we minimize unwanted
ENAs from Venus and solar background. The resulting spectra from the sky show an
influx of ENAs. The obtained spectra vary slightly across the sky and are in good
agreement with the expected ENA spectrum and intensity derived from in-situ ion
measurements by Voyager-1 and 2, and hydrogen gas density estimates from pick-up ion
measurements. |
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