The IBEX ribbon as a signature of the inhomogeneity of the local interstellar medium

Fichtner, H.; Scherer, K.; Effenberger, Frederic; Zönnchen, J.; Schwadron, N. A.; McComas, D. J.

doi:10.1051/0004-6361/201322064

Cited by 17 publications

(29 citation statements)

References 66 publications

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“…All models involve charge exchange between ions and neutral atoms. Alternatively, a density fluctuation in the neutral interstellar gas passing over the heliosphere has been proposed, which would cause a localized increase of the charge exchange, thus locally increasing the production of the globally distributed ENA flux [72].…”

Section: What Is the Correlation Between The Ibex Soho And Voyager mentioning

confidence: 99%

Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields

et al. 2017

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Publication resulting from an International ISSI Team of the same name. Submitted to Space Science ReviewsInternational audienceThis paper summarizes the results obtained by the team "Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields" supported by the International Space Science Institute in Bern, Switzerland. We focus on the physical processes occurring in the outer heliosphere, especially at its boundary called the heliopause (HP), and in the LISM. The importance of magnetic field, charge exchange between atoms and ions, and solar cycle on the heliopause topology and observed heliocentric distances to different heliospheric discontinuities are discussed. It is shown that time-dependent boundary conditions are necessary to describe the heliospheric asymmetries detected by the Voyager spacecraft. We also discuss the structure of the HP, especially due to its instability and magnetic reconnection. It is demonstrated that the Rayleigh-Taylor instability of the nose of the HP creates consecutive layers of the interstellar and heliospheric plasma which are magnetically connected to different sources. This may be a possible explanation of abrupt changes in the galactic and anomalous cosmic ray fluxes observed by Voyager 1 when it was crossing the HP structure for a period of about one month in the summer of 2012. This paper also discusses the plausibility of fitting simulation results to a number of observational data sets obtained by in situ and remote measurements. The distribution of magnetic field in the vicinity of the HP is discussed in the context of Voyager measurements. We discuss the transport of energetic particles in the inner and outer heliosheath, concentrating on the anisotropic spatial diffusion diffusion tensor and the pitch-angle dependence of perpendicular diffusion and demonstrate that the latter can explain the observed pitch-angle anisotropies of both the anomalous and galactic cosmic rays in the outer heliosheath

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Section: What Is the Correlation Between The Ibex Soho And Voyager mentioning

confidence: 99%

Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields

et al. 2017

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“…Whereas the plasma stagnation scenario postulates a region of enhanced plasma density in the inner heliosheath as the source of the Ribbon ENAs, a recent paper by Fichtner et al . [] explores the possibility that the Ribbon results from a localized enhancement of the interstellar neutral density in the inner heliosheath as the result of a sheet‐like neutral density structure in the local interstellar medium passing through the heliosphere. Referring to recent work on turbulence and inhomogeneities in the neutral and ionized components of the LISM, the authors propose that coupling between a field‐aligned compressive wave in the LISM plasma and interstellar neutral hydrogen can produce a localized density enhancement—an “ H wave” with an assumed scale size of a few 10s of AU—that propagates with the plasma along the interstellar magnetic field and is assumed to be oriented perpendicular to the field (Figure ).…”

Section: The Origin Of the Ribbonmentioning

confidence: 99%

IBEX's Enigmatic Ribbon in the sky and its many possible sources

2014

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Launched in October 2008, NASA's Interstellar Boundary Explorer (IBEX) has provided the first-ever energy-resolved all-sky maps of energetic neutral atom (ENA) emissions from the boundary of the heliosphere with the local interstellar medium (LISM). The maps reveal an enigmatic "Ribbon" of enhanced emissions superposed on a smoothly varying global distribution of ENA emissions. The Ribbon lies between the locations where the two Voyagers crossed the termination shock and was not sampled by them on their trajectories out through the heliosphere. IBEX's discovery of the Ribbon-a feature completely unpredicted by theory and numerical simulations-requires a new paradigm in our understanding of the heliosphere/LISM interaction. The Ribbon appears to be ordered by the interstellar magnetic field and the solar wind's latitudinal structure. The Ribbon's origin, whether from processes occurring in the heliosphere or beyond in the LISM, is unknown and the subject of intense investigation. Continued observations over the first 3 years of the IBEX mission have characterized the Ribbon, including its location, energy spectra, fine structure, and time variations. Here we review and compare the various hypotheses that have been proposed to explain the Ribbon, assess their ability to account for the features that have emerged from 3 years of careful analysis of the IBEX sky maps, and discuss how evolving theories and observations during IBEX's extended mission and by the National Research Council's recommended follow-on mission (the Interstellar Mapping and Acceleration Probe) will be used to finally determine the true source of the Ribbon.

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“…Since then, many of these have been developed into quantitative models, while other, completely new ideas have also arisen. Various models include sources near the termination shock (Kucharek et al 2013), in the IHS (Siewert et al 2013;Fichtner et al 2014; see also the quantitative calculation of the hydrogen (H)-wave scenario in Sylla & Fichtner 2015), in the OHS (Heerikhuisen et al 2010b;Chalov et al 2010;, or in the distant LISM (Grzedzielski et al 2010). For a review of hypothesized ribbon mechanisms, see McComas et al (2014) and references therein.…”

Section: Introductionmentioning

confidence: 99%

Effects of solar wind speed on the secondary energetic neutral source of the Interstellar Boundary Explorer ribbon

Zirnstein

Funsten

Heerikhuisen

et al. 2016

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The Interstellar Boundary EXplorer (IBEX) ribbon is an intense energetic neutral atom (ENA) emission feature encircling the sky, spanning energies ≤0.5-6 keV. The ribbon may be produced by the "secondary ENA" mechanism, where ENAs emitted from a source plasma population inside the heliosphere propagate outside the heliopause, undergo two charge-exchange events, and become secondary ENAs that may be directed back toward Earth and detected by IBEX. In this scenario, the source plasma population is governed by the interaction of the solar wind (SW) with the interstellar medium and is thus sensitive to the global SW properties. Moreover, this scenario predicts that the distance to the source of secondary ENAs depends on the ENA energy and SW speed, which in turn may affect the shape of the ribbon. In this paper, we use a computational model of the heliosphere with simplified SW boundary conditions to analyze the influence of ENA energy and SW speed, independent of time and latitude, on the global spatial and geometric properties of the ribbon. We find a strong dependence of the simulated ribbon energy spectrum and spatial symmetry on SW speed and ENA energy, and only a slight dependence on ribbon geometry. Our results suggest a significant number of primary ENAs from the inner heliosheath may contribute to the pickup ion source population outside the heliopause, depending on the ENA energy and SW speed. The lack of variation in the simulated ribbon center as a function of ENA energy and SW speed, in contrast to the observations, implies that the asymmetry of the SW plays an important role in determining the position of the ribbon. Comparisons to the IBEX data also signify the ribbon's dependence on the properties of the local interstellar medium, particularly the interstellar magnetic field.

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The IBEX ribbon as a signature of the inhomogeneity of the local interstellar medium

Cited by 17 publications

References 66 publications

Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields

Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields

IBEX's Enigmatic Ribbon in the sky and its many possible sources

Effects of solar wind speed on the secondary energetic neutral source of the Interstellar Boundary Explorer ribbon

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