Energetic neutral atom imaging of the heliospheric boundary region

Gruntman, M.; Roelof, E. C.; Mitchell, D. G.; Fahr, H. J.; Funsten, H. O.; McComas, D. J.

doi:10.1029/2000ja000328

Cited by 131 publications

(135 citation statements)

References 92 publications

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“…The neutral density has been taken to be n n ≈ 5 × 10 13 km −3 . The survival probability p surv of hydrogen atoms with energies of more than 55 keV to reach Earth's orbit from the heliosheath is close to unity (Gruntman et al 2001). At energies of 58-88 keV/amu the dimensionless parameter w is of order w ≈ 80.…”

Section: Acceleration Of Pick-up Ions In the Subsonic Solar Windmentioning

confidence: 93%

“…Figure 6 shows the model functions and spacecraft data for four stationary situations: suprathermal tails of the slow or fast solar wind fed into either the upwind heliosheath or into the heliotail, respectively. Charge exchange cross sections σ(v) and survival probabilities p surv are incorporated numerically from (Gruntman et al 2001). We note that the ENA flux detected by HSTOF near Earth's orbit is compatible with the stationary situation when the typical suprathermal tails of the slow solar wind are fed into the heliosheath for both the apex and the anti-apex direction.…”

Section: Acceleration Of Pick-up Ions In the Subsonic Solar Windmentioning

confidence: 99%

“…Without solving the full self-consistent problem, the damping of Alfvén waves can be described by replacing ρ HP by ρ TS + ∆ρ A , where ∆ρ A is the damping length of the Alfvén waves. The differential flux j ENA (v) = f ENA (v)v 2 /m of ENAs near Earth's orbit in units of cm −2 s −1 keV −1 amu sr −1 is calculated from the phase space density f PUI (v, ρ) in s 3 km −6 of heliospheric suprathermal pick-up ions (Gruntman et al 2001) as…”

Section: Acceleration Of Pick-up Ions In the Subsonic Solar Windmentioning

confidence: 99%

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On the “injection problem” at the solar wind termination shock

Kallenbach

Hilchenbach

Chalov

et al. 2005

A&A

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Abstract. This article presents an integrated analytical model on the injection efficiencies of the different ion species of the Anomalous component of the Cosmic Rays (ACRs) at the solar wind termination shock. We find that the injection into diffusive (first-order Fermi) acceleration is dominated by parallel ion diffusion and not by perpendicular diffusion unless the angle Ψ between the shock normal and the heliospheric magnetic field is almost exactly 90 • (89.3 • < Ψ ≈ 90 • ). In steady state the threshold speed for injection into first-order Fermi acceleration at a not exactly perpendicular solar wind termination shock -with the Parker shock angle Ψ ≈ 89.3 • -adjusts itself self-consistently. Increased anisotropic ACR flux amplifies Alfvénic turbulence which in turn suppresses parallel diffusion. It therefore increases the injection threshold and decreases the ACR flux until equilibrium is reached. For this equilibrium situation, we estimate the injection efficiencies of different species of suprathermal ions at the termination shock. We consider the following pre-acceleration processes: 1) momentum diffusion in compressional (ion-acoustic and magnetosonic) turbulence in the upstream supersonic solar wind and adiabatic cooling during convection to the termination shock; 2) reflection, transmission, and acceleration in the electric potential of the termination shock; and 3) momentum diffusion (stochastic or second-order Fermi acceleration) in the subsonic solar wind downstream of the termination shock in the inner heliosheath region. Our model results are compared to data from instruments on board the SOHO, ACE, Ulysses, and Voyager spacecraft.

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Section: Acceleration Of Pick-up Ions In the Subsonic Solar Windmentioning

confidence: 93%

Section: Acceleration Of Pick-up Ions In the Subsonic Solar Windmentioning

confidence: 99%

Section: Acceleration Of Pick-up Ions In the Subsonic Solar Windmentioning

confidence: 99%

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On the “injection problem” at the solar wind termination shock

Kallenbach

Hilchenbach

Chalov

et al. 2005

A&A

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“…The spectrum can be divided into three parts: the Maxwellian-like distribution of the thermal core, the broad distribution of pickup ions extending up to twice the upstream solar wind speed, and the power law distribution of the suprathermal tail. Previous studies of heliospheric ENAs [e.g., Gruntman et al, 2001] approximated the downstream ions as a Maxwellian core, a Maxwellian core plus a spherical distribution of pickup ions, or a Maxwellian core plus a Maxwellian distribution of pickup ions. Prior to this paper, to our knowledge no ENA flux calculation has included a power law tail.…”

Section: Introductionmentioning

confidence: 99%

Implications of solar wind suprathermal tails for IBEX ENA images of the heliosheath

et al. 2008

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[1] Decades of interplanetary measurements of the solar wind and other space plasmas have established that the suprathermal ion intensity distributions (j) are non-Maxwellian and are characterized by high-energy power law tails (j $ E Àk ). Recent analysis by Fisk and Gloeckler of suprathermal ion observations between 1-5 AU demonstrates that a particular differential intensity distribution function emerges universally between $2-10 times the solar wind speed with k $ 1.5. This power law tail is particularly apparent in downstream distributions beyond reverse shocks associated with corotating interaction regions. Similar power law tails have been observed in the downstream flow beyond the termination shock by the Low Energy Charged Particle instrument on both Voyager 1 and Voyager 2. Using kappa distributions with internal energy, density, and bulk flow derived from large-scale magnetohydrodynamic models, we calculate the simulated flux of energetic neutral atoms (ENAs) produced in the heliosheath by charge exchange between solar wind protons and interstellar hydrogen. We then produce simulated ENA maps of the heliosheath, such as will be measured by the Interstellar Boundary Explorer Mission (IBEX). We also estimate the expected signal to noise and background ratio for IBEX. The solar wind suprathermal tail significantly increases the ENA flux within the IBEX energy range, $0.01-6 keV, by more than an order of magnitude at the highest energies over the estimates using a Maxwellian. It is therefore essential to consider suprathermal tails in the interpretation of IBEX ENA images and theoretical modeling of the heliospheric termination shock.

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“…For the globally distributed flux, the dominant parent ion source for neutrals in the energy range above 1 keV is likely ions that were originally picked up in the heliosphere before the solar wind encountered the termination shock (e.g., Gruntman et al 2001;Prested et al 2008;Gloeckler & Fisk 2010). The neutrals are produced by ionization (pick up) of interstellar neutrals by the solar wind in the heliosphere, transport of these ions across the termination shock with the solar wind, charge exchange in the heliosheath downstream of the termination shock, and return of these neutrals back to the inner heliosphere.…”

Section: Introductionmentioning

confidence: 99%

HELIOSPHERIC NEUTRAL ATOM SPECTRA BETWEEN 0.01 AND 6 keV FROMIBEX

Fuselier

Allegrini

Bzowski

et al. 2012

ApJ

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Since 2008 December, the Interstellar Boundary Explorer (IBEX) has been making detailed observations of neutrals from the boundaries of the heliosphere using two neutral atom cameras with overlapping energy ranges. The unexpected, yet defining feature discovered by IBEX is a Ribbon that extends over the energy range from about 0.2 to 6 keV. This Ribbon is superposed on a more uniform, globally distributed heliospheric neutral population. With some important exceptions, the focus of early IBEX studies has been on neutral atoms with energies greater than ∼0.5 keV. With nearly three years of science observations, enough low-energy neutral atom measurements have been accumulated to extend IBEX observations to energies less than ∼0.5 keV. Using the energy overlap of the sensors to identify and remove backgrounds, energy spectra over the entire IBEX energy range are produced. However, contributions by interstellar neutrals to the energy spectrum below 0.2 keV may not be completely removed. Compared with spectra at higher energies, neutral atom spectra at lower energies do not vary much from location to location in the sky, including in the direction of the IBEX Ribbon. Neutral fluxes are used to show that low energy ions contribute approximately the same thermal pressure as higher energy ions in the heliosheath. However, contributions to the dynamic pressure are very high unless there is, for example, turbulence in the heliosheath with fluctuations of the order of 50-100 km s −1 .

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Energetic neutral atom imaging of the heliospheric boundary region

Cited by 131 publications

References 92 publications

On the “injection problem” at the solar wind termination shock

On the “injection problem” at the solar wind termination shock

Implications of solar wind suprathermal tails for IBEX ENA images of the heliosheath

HELIOSPHERIC NEUTRAL ATOM SPECTRA BETWEEN 0.01 AND 6 keV FROMIBEX

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