Microstructure of the Heliospheric Termination Shock: Implications for Energetic Neutral Atom Observations

Zank, G. P.; Heerikhuisen, J.; Pogorelov, N. V.; Burrows, R.; McComas, D. J.

doi:10.1088/0004-637x/708/2/1092

Cited by 175 publications

(207 citation statements)

References 29 publications

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“…However, fluxes in this energy range from ∼1 to 6 keV from most regions of the sky (excluding the IBEX Ribbon) are in relatively good agreement with results from the latest heliosphere/ISM models (Desai et al 2014;Zank et al 2010), and there is general agreement on how these ENAs are produced. IBEX observes a power law or a Kappa distribution over this energy range with a power law index of ∼-1.5 to −3 (Funsten et al 2009b;McComas et al 2009b).…”

Section: Introductionsupporting

confidence: 74%

Low Energy Neutral Atoms From the Heliosheath

Fuselier

Allegrini

Bzowski

et al. 2014

ApJ

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In the heliosheath beyond the termination shock, low energy (<0.5 keV) neutral atoms are created by charge exchange with interstellar neutrals. Detecting these neutrals from Earth's orbit is difficult because their flux is reduced substantially by ionization losses as they propagate from about 100 to 1 AU and because there are a variety of other signals and backgrounds that compete with this weak signal. Observations from IBEX-Lo and -Hi from two opposing vantage points in Earth's orbit established a lower energy limit of about 0.1 keV on measurements of energetic neutral atoms (ENAs) from the heliosphere and the form of the energy spectrum from about 0.1 to 6 keV in two directions in the sky. Below 0.1 keV, the detailed ENA spectrum is not known, and IBEX provides only upper limits on the fluxes. However, using some assumptions and taking constraints on the spectrum into account, we find indications that the spectrum turns over at an energy between 0.1 and 0.2 keV.

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Section: Introductionsupporting

confidence: 74%

Low Energy Neutral Atoms From the Heliosheath

Fuselier

Allegrini

Bzowski

et al. 2014

ApJ

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“…Even though the Voyager observations of the TS suggest that the downstream plasma is still supersonic, this may be misleading because the Voyagers are unable to observe all plasma components of the solar wind. For example, several recent multicomponent studies of the solar wind (Wu et al 2009;Zank et al 2010) suggested that the downstream plasma is composed of thermal protons, nonthermal PUIs and also energetic electrons, and that excludsing some of these components from the model may result in a strong overestimate of downstream Mach numbers. In fact, with hot electrons taken into account, effective downstream Mach numbers ofM s2 10 −1 are obtained, which allows us to assume incompressibility of the plasma.…”

Section: Removing Ena Candidates Along a Flow Linementioning

confidence: 99%

“…thermal solar wind, pick-up ions) of the plasma flow in this region (see e.g. Zank et al 2010;Livadiotis et al 2011;Siewert et al 2013). In contrast to this, identifying a possible modulation of more distant sources beyond the heliopause is less trivial because of the specific configurations and assumptions used by models devoted to these sources (see e.g.…”

Section: Introductionmentioning

confidence: 99%

Transit-time aspects of ENA production models for the inner heliosheath

Siewert

Fahr

McComas

2014

A&A

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It is still a major challenge to understand the data of energetic neutral atoms (ENAs) that arrive from the outer heliosphere. These data are provided by the IBEX mission. With the most recent data covering three years of dynamical evolution, it is now possible to study temporal correlations with the solar cycle. We present in this paper for the first time an extended study dedicated to the transit-time delay between the plasma that is ejected from the Sun towards the outer heliosphere and the ENA fluxes that reach the detector after the solar wind protons undergo charge exchange processes in their distant production regions in the inner heliosheath. We derive transit-time delays caused by both general and non-trivial model-dependent contributions for arbitrary points in the inner heliosheath. In addition, we also calculate the average transit-time delay along the line-of-sight in selected directions, allowing to estimate how strongly an extended emission region can reduce the resolution that is possible with transit-time studies. We are able to demonstrate that ENAs generated beyond a certain characteristic streamline distance are mostly removed by charge exchange, and thus do not contribute significantly to the keV-ENA fluxes observed by IBEX. For this reason, transit-time delays do provide a viable tool for studying the impact of the solar cycle on ENA fluxes.

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“…These models do not yield a self-consistent description of the pickup ions; therefore, additional assumptions are needed to link the upstream pickup ion pressure with the downstream pickup ion pressure across the termination shock [Zank et al, 1996[Zank et al, , 2010Fahr and Chalov, 2008]. The truly self-consistent treatment of the thermodynamics of each ion species and electrons is implemented in multi-ion multifluid MHD models [Harnett and Winglee, 2006;Glocer et al, 2009;Najib et al, 2011;Tóth et al, 2012].…”

Section: Introductionmentioning

confidence: 99%

Constraining the pickup ion abundance and temperature through the multifluid reconstruction of the Voyager 2 termination shock crossing

et al. 2015

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Voyager 2 observations revealed that the hot solar wind ions (the so‐called pickup ions) play a dominant role in the thermodynamics of the termination shock and the heliosheath. The number density and temperature of this hot population, however, have remained unknown, since the plasma instrument on board Voyager 2 can only detect the colder thermal ion component. Here we show that due to the multifluid nature of the plasma, the fast magnetosonic mode splits into a low‐frequency fast mode and a high‐frequency fast mode. The coupling between the two fast modes results in a quasi‐stationary nonlinear wave mode, the “oscilliton,” which creates a large‐amplitude trailing wave train downstream of the thermal ion shock. By fitting multifluid shock wave solutions to the shock structure observed by Voyager 2, we are able to constrain both the abundance and the temperature of the undetected pickup ions. In our three‐fluid model, we take into account the nonnegligible partial pressure of suprathermal energetic electrons (0.022–1.5 MeV) observed by the Low‐Energy Charged Particle Experiment instrument on board Voyager 2. The best fitting simulation suggests a pickup ion abundance of 20 ± 3%, an upstream pickup ion temperature of 13.4 ± 2 MK, and a hot electron population with an apparent temperature of ~0.83 MK. We conclude that the actual shock transition is a subcritical dispersive shock wave with low Mach number and high plasma β.

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Microstructure of the Heliospheric Termination Shock: Implications for Energetic Neutral Atom Observations

Cited by 175 publications

References 29 publications

Low Energy Neutral Atoms From the Heliosheath

Low Energy Neutral Atoms From the Heliosheath

Transit-time aspects of ENA production models for the inner heliosheath

Constraining the pickup ion abundance and temperature through the multifluid reconstruction of the Voyager 2 termination shock crossing

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