The Interstellar Boundary Explorer High Energy (IBEX-Hi) Neutral Atom Imager

Abstract

The IBEX-Hi Neutral Atom Imager of the Interstellar Boundary Explorer (IBEX) mission is designed to measure energetic neutral atoms (ENAs) originating from the interaction region between the heliosphere and the local interstellar medium (LISM). These ENAs are plasma ions that have been heated in the interaction region and neutralized by charge exchange with the cold neutral atoms of the LISM that freely flow through the interaction region. IBEX-Hi is a single pixel ENA imager that covers the ENA spectral range from 0.38 H.O. Funsten et al. to 6 keV and shares significant energy overlap and overall design philosophy with the IBEXLo sensor. Because of the anticipated low flux of these ENAs at 1 AU, the sensor has a large geometric factor and incorporates numerous techniques to minimize noise and backgrounds. The IBEX-Hi sensor has a field-of-view (FOV) of 6.5°× 6.5°FWHM, and a 6.5°× 360°s wath of the sky is imaged over each spacecraft spin. IBEX-Hi utilizes an ultrathin carbon foil to ionize ENAs in order to measure their energy by subsequent electrostatic analysis. A multiple coincidence detection scheme using channel electron multiplier (CEM) detectors enables reliable detection of ENAs in the presence of substantial noise. During normal operation, the sensor steps through six energy steps every 12 spacecraft spins. Over a single IBEX orbit of about 8 days, a single 6.5°× 360°swath of the sky is viewed, and re-pointing of the spin axis toward the Sun near perigee of each IBEX orbit moves the ecliptic longitude by about 8°every orbit such that a full sky map is acquired every six months. These global maps, covering the spectral range of IBEX-Hi and coupled to the IBEX-Lo maps at lower and overlapping energies, will answer fundamental questions about the structure and dynamics of the interaction region between the heliosphere and the LISM.Keywords Interstellar boundary · Termination shock · Heliopause · Energetic neutral atom · ENA · LISM PACS 96.50.-e · 96.50.Ek · 96.50.Xy · 96.50.Zc

Heavy coronal ions in the heliosphere

“…It features two singlepixel, neutral atom cameras: IBEX-Hi (Funsten et al 2009) and IBEX-Lo (Fuselier et al 2009). Basically only IBEX-Lo has the capability of discerning species of the incoming atoms, including (indirectly) neutral He (Möbius et al 2009), and IBEX-Hi was designed to observe neutral H. Allegrini et al (2008) suggest an ingeneous technique by which some other species, including He, might also be registered owing to a special treatment of data from the IBEX-Hi anti-coincidence system.…”

OBSERVATIONS OF ISOTROPIC INTERSTELLAR PICK-UP IONS AT 11 AND 17 AU FROMNEW HORIZONS

“…Since the spectra are measured in the spacecraft frame, we transform the model distributions, Equations (1) and (2), from the solar wind frame into the spacecraft frame using a non-relativistic velocity transformation, v + u = v c + v m , where v c is the velocity of the spacecraft relative to the Sun, and u is the solar wind bulk velocity, which we assume to be constant and in the radial direction for this analysis. An instrument's geometric factor, G, is defined by an integration of the response function R(v m ; V ) over v m and is related proportionally to the measured count rate (Funsten et al 2009;Johnstone et al 1987;Hundhausen et al 1967). Typically for ESA-based instruments, the geometric factor, G, is assumed to be independent of E/q.…”

FIRST SKY MAP OF THE INNER HELIOSHEATH TEMPERATURE USINGIBEXSPECTRA

“…McNutt et al (1999) already provided the proton-hydrogen chargeexchange cross section in the power law form σ (ε) ∼ = σ 0 · ε −b cs , with σ 0 ≈ 2.4280 × 10 −15 cm 2 and b cs ≈ 0.1327, which is valid over an energy range that includes the IBEX-Hi energy channels #2-6 with range 0.71-4.29 keV (Funsten et al 2009b). (Throughout this work, energy will be given in keV.)…”