Heliospheric energetic neutral atom intensities at 1 AU derived from global fitting of the IBEX-HI data set
Abstract
During a single orbit, the Interstellar Boundary Explorer (IBEX) instruments measure Energetic Neutral Atoms (ENAs) arriving at the spacecraft approximately perpendicular to the Earth/Sun line. Since IBEX spins about a Sun-centered axis, each IBEX spin yields measurements of the region of the heliopause/termination shock whose ENAs arrive within a small angle of a great circle on the sky (7 degrees FWHM is the instantaneous field of view of the IBEX-HI telescope) perpendicular to the Earth/Sun line. As the Earth revolves around the Sun, this great circle is made to precess at the same rate, yielding a map of ENA intensity arriving at 1 AU over the entire sky every six months. Because of occasional contamination of the ENA images by local energetic particle fluxes (e.g., solar wind, magnetospheric ENAs, etc.), each ~7-day IBEX orbit must be culled individually. There remains the possibility of a residual background population in the images. ENAs from a heliospheric source exhibit aberration due to the Earth's motion around the Sun. This serves as a constraint which allows us to separate signal of heliospheric origin from unwanted counts that exhibit an isotropic (in the spacecraft frame) distribution. Under the assumption that this residuum has no dependence on IBEX spin phase around the great circle, we obtain an optimized estimate of the incident ENA intensity plus a residual (spin-phase-independent but energy-dependent) background rate for each particular orbit. This is done for all six energy channels (centers from 0.4-4.5 keV) of IBEX-HI. By combining data from a large portion of the mission, we can estimate the ENA intensities and the local background, as well as the time dependence of both. It is important to note that time dependences of the ENA intensities on scales shorter than six months (e.g., changes introduced by transmission through the heliosphere) can only be resolved on average and further work needs to be done to account for these higher frequency effects. We give here a summary of the algorithms involved in the global ENA intensity determination, an overview of the resulting all-sky maps, as well as directions for future improvements in the technique.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMSH21A1799D
- Keywords:
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- 1910 INFORMATICS / Data assimilation;
- integration and fusion;
- 2114 INTERPLANETARY PHYSICS / Energetic particles;
- 2124 INTERPLANETARY PHYSICS / Heliopause and solar wind termination;
- 2126 INTERPLANETARY PHYSICS / Heliosphere/interstellar medium interactions