The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
D J Mccomas - One of the best experts on this subject based on the ideXlab platform.
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simulation of the solar wind dynamic pressure increase in 2014 and its effect on energetic Neutral Atom fluxes from the heliosphere
The Astrophysical Journal, 2018Co-Authors: E J Zirnstein, J Heerikhuisen, D J Mccomas, N V Pogorelov, D B Reisenfeld, J R SzalayAbstract:In late 2014, the solar wind dynamic pressure increased by ~50% over a relatively short time (~6 months). In early 2017, the Interstellar Boundary Explorer (IBEX) observed an increase in heliospheric energetic Neutral Atom (ENA) fluxes from directions near the front of the heliosphere. These enhanced ENA emissions resulted from the increase in SW pressure propagating through the inner heliosheath (IHS), affecting the IHS plasma pressure and emission of ~keV ENA fluxes. We expand on the analysis by McComas et al. on the effects of this pressure change on ENA fluxes observed at 1 au using a three-dimensional, time-dependent simulation of the heliosphere. The pressure front has likely already crossed the termination shock (TS) in all directions, but ENA fluxes observed at 1 au will change over the coming years, as the TS, heliopause, and IHS plasma pressure continue to change in response to the SW pressure increase. Taken in isolation, the pressure front creates a "ring" of increasing ENA fluxes projected in the sky that expands in angular radius over time, as a function of the distances to the heliosphere boundaries and the ENA propagation speed. By tracking the position of this ring over time in our simulation, we demonstrate a method for estimating the distances to the TS, heliopause, and ENA source region that can be applied to IBEX data. This will require IBEX observations at 4.3 keV up through ~2020, and longer times at lower ENA energies, in order to observe significant changes from the heliotail.
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circularity of the interstellar boundary explorer ribbon of enhanced energetic Neutral Atom ena flux
The Astrophysical Journal, 2013Co-Authors: H O Funsten, J Heerikhuisen, D J Mccomas, P H Janzen, R Demajistre, P C Frisch, B A Larsen, David Higdon, G LivadiotisAbstract:As a sharp feature in the sky, the ribbon of enhanced energetic Neutral Atom (ENA) flux observed by the Interstellar Boundary Explorer (IBEX) mission is a key signature for understanding the interaction of the heliosphere and the interstellar medium through which we are moving. Over five nominal IBEX energy passbands (0.7, 1.1, 1.7, 2.7, and 4.3 keV), the ribbon is extraordinarily circular, with a peak location centered at ecliptic (λRC, βRC) = (219.°2 ± 1.°3, 39.°9 ± 2.°3) and a half cone angle of C = 74.°5 ± 2.°0. A slight elongation of the ribbon, generally perpendicular to the ribbon center-heliospheric nose vector and with eccentricity ~0.3, is observed over all energies. At 4.3 keV, the ribbon is slightly larger and displaced relative to lower energies. For all ENA energies, a slice of the ribbon flux peak perpendicular to the circular arc is asymmetric and systematically skewed toward the ribbon center. We derive a spatial coherence parameter δC ≤ 0.014 that characterizes the spatial uniformity of the ribbon over its extent in the sky and is a key constraint for understanding the underlying processes and structure governing the ribbon ENA emission.
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effects of fast and slow solar wind on the energetic Neutral Atom ena spectra measured by the interstellar boundary explorer ibex at the heliospheric poles
The Astrophysical Journal, 2012Co-Authors: M A Dayeh, D J Mccomas, F Allegrini, H O Funsten, M I Desai, B De Majistre, P H JanzenAbstract:We study the energy dependence of ~0.5-6 keV energetic Neutral Atom (ENA) spectra in the southern heliospheric polar region obtained during five six-month sky maps measured by IBEX-Hi. We calculate the spectral slopes in the south pole in four different energy bands, namely, ~0.7-1.1 keV, ~1.1-1.7 keV, ~1.7-2.7 keV, and ~2.7-4.3 keV. We show (1) a persistent flattening of the ENA spectrum between ~1 and 2 keV, (2) significantly different modes (2.31, 1.58, 0.97, and 1.44) for the distributions of the slopes in the four different energy bands, and (3) a general decrease with increasing energy in the widths (FWHM) and mode fluctuations (their spread) of the slope distributions. We also compare the averaged ENA spectra measured at the south pole and at mid-latitudes. We conclude that the flattening between ~1 and 2 keV in the polar spectrum (spectral break) is produced by an enhancement of ENAs created by charge exchange between interstellar Neutrals and pick-up ions in the fast solar wind.
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two wide angle imaging Neutral Atom spectrometers and interstellar boundary explorer energetic Neutral Atom imaging of the 5 april 2010 substorm
Journal of Geophysical Research, 2012Co-Authors: D J Mccomas, N Buzulukova, Martin Connors, M A Dayeh, J Goldstein, H O FunstenAbstract:[1] This study is the first to combine energetic Neutral Atom (ENA) observations from Two Wide-Angle Imaging Neutral-Atom Spectrometers (TWINS) and Interstellar Boundary Explorer (IBEX). Here we examine the arrival of an interplanetary shock and the subsequent geomagnetically effective substorm on 5 April 2010, which was associated with the Galaxy 15 communications satellite anomaly. IBEX shows sharply enhanced ENA emissions immediately upon compression of the dayside magnetosphere at 08:26:17+/−9 s UT. The compression drove a markedly different spectral shape for the dayside emissions, with a strong enhancement at energies >1 keV, which persisted for hours after the shock arrival, consistent with the higher solar wind speed, density, and dynamic pressure (∼10 nPa) after the shock. TWINS ENA observations indicate a slower response of the ring current and precipitation of ring current ions as low-altitude emissions ∼15 min later, with the >50 keV ion precipitation leading the <10 keV precipitation by ∼20 min. These observations suggest internal magnetospheric processes are occurring after compression of the magnetosphere and before the ring current ions end up in the loss cone and precipitate into the ionosphere. We also compare MHD simulation results with both the TWINS and IBEX ENA observations; while the overall fluxes and distributions of emissions were generally similar, there were significant quantitative differences. Such differences emphasize the complexity of the magnetospheric system and importance of the global perspective for macroscopic magnetospheric studies. Finally, Appendix A documents important details of the TWINS data processing, including improved binning procedures, smoothing of images to a given level of statistical accuracy, and differential background subtraction.
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Neutral Atom imaging of the magnetospheric cusps
Journal of Geophysical Research, 2011Co-Authors: S M Petrinec, D J Mccomas, S A Fuselier, H O Funsten, D Heirtzler, P H Janzen, M A Dayeh, H Kucharek, E MobiusAbstract:[1] The magnetospheric cusps separate closed dayside magnetospheric field lines from open field lines of the magnetotail mantle and lobes. All magnetospheric field lines that map to the magnetopause also pass through the cusp regions. Thus whenever magnetic reconnection occurs at the magnetopause, magnetosheath plasma can enter one or both of the cusp regions and charge exchange with the geocorona. The resulting energetic Neutral Atoms (ENAs) resulting from this charge exchange process propagate away from the cusps and are observed remotely by the Interstellar Boundary Explorer (IBEX). The asymmetry of the ENA intensities between the northern and southern cusps are strongly dependent upon the Earth's dipole tilt angle and are consistent with in situ cusp observations. These asymmetric fluxes in the cusp regions are suggested to be explained by the regions at the magnetopause where magnetic reconnection is expected.
H O Funsten - One of the best experts on this subject based on the ideXlab platform.
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symmetry of the ibex ribbon of enhanced energetic Neutral Atom ena flux
The Astrophysical Journal, 2015Co-Authors: H O Funsten, J Heerikhuisen, M Bzowski, P H Janzen, R Demajistre, M A Dayeh, D M Cai, P C Frisch, Dave Higdon, B A LarsenAbstract:The circular ribbon of enhanced energetic Neutral Atom (ENA) emission observed by the Interstellar Boundary Explorer (IBEX) mission remains a critical signature for understanding the interaction between the heliosphere and the interstellar medium. We study the symmetry of the ribbon flux and find strong, spectrally dependent reflection symmetry throughout the energy range 0.7-4.3?keV. The distribution of ENA flux around the ribbon is predominantly unimodal at 0.7 and 1.1?keV, distinctly bimodal at 2.7 and 4.3?keV, and a mixture of both at 1.7?keV. The bimodal flux distribution consists of partially opposing bilateral flux lobes, located at highest and lowest heliographic latitude extents of the ribbon. The vector between the ribbon center and heliospheric nose (which defines the so-called BV plane) appears to play an organizing role in the spectral dependence of the symmetry axis locations as well as asymmetric contributions to the ribbon flux. The symmetry planes at 2.7 and 4.3?keV, derived by projecting the symmetry axes to a great circle in the sky, are equivalent to tilting the heliographic equatorial plane to the ribbon center, suggesting a global heliospheric ordering. The presence and energy dependence of symmetric unilateral and bilateral flux distributions suggest strong spectral filtration from processes encountered by an ion along its journey from the source plasma to its eventual detection at IBEX.
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circularity of the interstellar boundary explorer ribbon of enhanced energetic Neutral Atom ena flux
The Astrophysical Journal, 2013Co-Authors: H O Funsten, J Heerikhuisen, D J Mccomas, P H Janzen, R Demajistre, P C Frisch, B A Larsen, David Higdon, G LivadiotisAbstract:As a sharp feature in the sky, the ribbon of enhanced energetic Neutral Atom (ENA) flux observed by the Interstellar Boundary Explorer (IBEX) mission is a key signature for understanding the interaction of the heliosphere and the interstellar medium through which we are moving. Over five nominal IBEX energy passbands (0.7, 1.1, 1.7, 2.7, and 4.3 keV), the ribbon is extraordinarily circular, with a peak location centered at ecliptic (λRC, βRC) = (219.°2 ± 1.°3, 39.°9 ± 2.°3) and a half cone angle of C = 74.°5 ± 2.°0. A slight elongation of the ribbon, generally perpendicular to the ribbon center-heliospheric nose vector and with eccentricity ~0.3, is observed over all energies. At 4.3 keV, the ribbon is slightly larger and displaced relative to lower energies. For all ENA energies, a slice of the ribbon flux peak perpendicular to the circular arc is asymmetric and systematically skewed toward the ribbon center. We derive a spatial coherence parameter δC ≤ 0.014 that characterizes the spatial uniformity of the ribbon over its extent in the sky and is a key constraint for understanding the underlying processes and structure governing the ribbon ENA emission.
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heliospheric Neutral Atom spectra between 0 01 and 6 kev from ibex
The Astrophysical Journal, 2012Co-Authors: S A Fuselier, F Allegrini, M Bzowski, H O Funsten, A G Ghielmetti, G Gloeckler, D Heirtzler, P H JanzenAbstract: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 locationtolocationinthesky,includinginthedirectionoftheIBEXRibbon.Neutralfluxesareusedtoshowthatlow 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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exploring the time dispersion of the ibex hi energetic Neutral Atom spectra at the ecliptic poles
The Astrophysical Journal, 2012Co-Authors: S A Fuselier, F Allegrini, M Bzowski, H O Funsten, R Demajistre, M A Dayeh, M I DesaiAbstract:The Interstellar Boundary Explorer (IBEX) has observed energetic Neutral Atom (ENA) hydrogen emissions from the edge of the solar system for more than three years. The observations span energies from 0.01 to 6?keV FWHM. At energies greater than 0.5-6?keV, and for a travel distance of ~100?AU, the travel time difference between the slowest and the fastest ENA is more than a year. Therefore, we construct spectra including the effect that slower ENAs left the source at an earlier time than faster ones. If the source produces a steady rate of ENAs and the extinction does not vary, then we expect that the spectral shape would be time independent. However, while the extinction of ENAs has been fairly constant during the first two and a half years, the source appears to have changed, and thus the spectra at a single time may not represent the conditions at the source. IBEX's viewing allows continuous sampling of the ecliptic poles where fluxes can be continuously monitored. For a given source distance we construct spectra assuming that the measured ENAs left the source at roughly the same time. To accomplish this construction, we apply time lag corrections to the signal at different ENA energies that take into account the travel time difference. We show that the spectral shape at the poles exhibits a statistically significant change with time.
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effects of fast and slow solar wind on the energetic Neutral Atom ena spectra measured by the interstellar boundary explorer ibex at the heliospheric poles
The Astrophysical Journal, 2012Co-Authors: M A Dayeh, D J Mccomas, F Allegrini, H O Funsten, M I Desai, B De Majistre, P H JanzenAbstract:We study the energy dependence of ~0.5-6 keV energetic Neutral Atom (ENA) spectra in the southern heliospheric polar region obtained during five six-month sky maps measured by IBEX-Hi. We calculate the spectral slopes in the south pole in four different energy bands, namely, ~0.7-1.1 keV, ~1.1-1.7 keV, ~1.7-2.7 keV, and ~2.7-4.3 keV. We show (1) a persistent flattening of the ENA spectrum between ~1 and 2 keV, (2) significantly different modes (2.31, 1.58, 0.97, and 1.44) for the distributions of the slopes in the four different energy bands, and (3) a general decrease with increasing energy in the widths (FWHM) and mode fluctuations (their spread) of the slope distributions. We also compare the averaged ENA spectra measured at the south pole and at mid-latitudes. We conclude that the flattening between ~1 and 2 keV in the polar spectrum (spectral break) is produced by an enhancement of ENAs created by charge exchange between interstellar Neutrals and pick-up ions in the fast solar wind.
F Allegrini - One of the best experts on this subject based on the ideXlab platform.
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heliospheric Neutral Atom spectra between 0 01 and 6 kev from ibex
The Astrophysical Journal, 2012Co-Authors: S A Fuselier, F Allegrini, M Bzowski, H O Funsten, A G Ghielmetti, G Gloeckler, D Heirtzler, P H JanzenAbstract: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 locationtolocationinthesky,includinginthedirectionoftheIBEXRibbon.Neutralfluxesareusedtoshowthatlow 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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exploring the time dispersion of the ibex hi energetic Neutral Atom spectra at the ecliptic poles
The Astrophysical Journal, 2012Co-Authors: S A Fuselier, F Allegrini, M Bzowski, H O Funsten, R Demajistre, M A Dayeh, M I DesaiAbstract:The Interstellar Boundary Explorer (IBEX) has observed energetic Neutral Atom (ENA) hydrogen emissions from the edge of the solar system for more than three years. The observations span energies from 0.01 to 6?keV FWHM. At energies greater than 0.5-6?keV, and for a travel distance of ~100?AU, the travel time difference between the slowest and the fastest ENA is more than a year. Therefore, we construct spectra including the effect that slower ENAs left the source at an earlier time than faster ones. If the source produces a steady rate of ENAs and the extinction does not vary, then we expect that the spectral shape would be time independent. However, while the extinction of ENAs has been fairly constant during the first two and a half years, the source appears to have changed, and thus the spectra at a single time may not represent the conditions at the source. IBEX's viewing allows continuous sampling of the ecliptic poles where fluxes can be continuously monitored. For a given source distance we construct spectra assuming that the measured ENAs left the source at roughly the same time. To accomplish this construction, we apply time lag corrections to the signal at different ENA energies that take into account the travel time difference. We show that the spectral shape at the poles exhibits a statistically significant change with time.
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effects of fast and slow solar wind on the energetic Neutral Atom ena spectra measured by the interstellar boundary explorer ibex at the heliospheric poles
The Astrophysical Journal, 2012Co-Authors: M A Dayeh, D J Mccomas, F Allegrini, H O Funsten, M I Desai, B De Majistre, P H JanzenAbstract:We study the energy dependence of ~0.5-6 keV energetic Neutral Atom (ENA) spectra in the southern heliospheric polar region obtained during five six-month sky maps measured by IBEX-Hi. We calculate the spectral slopes in the south pole in four different energy bands, namely, ~0.7-1.1 keV, ~1.1-1.7 keV, ~1.7-2.7 keV, and ~2.7-4.3 keV. We show (1) a persistent flattening of the ENA spectrum between ~1 and 2 keV, (2) significantly different modes (2.31, 1.58, 0.97, and 1.44) for the distributions of the slopes in the four different energy bands, and (3) a general decrease with increasing energy in the widths (FWHM) and mode fluctuations (their spread) of the slope distributions. We also compare the averaged ENA spectra measured at the south pole and at mid-latitudes. We conclude that the flattening between ~1 and 2 keV in the polar spectrum (spectral break) is produced by an enhancement of ENAs created by charge exchange between interstellar Neutrals and pick-up ions in the fast solar wind.
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separation of the interstellar boundary explorer ribbon from globally distributed energetic Neutral Atom flux
The Astrophysical Journal, 2011Co-Authors: F Allegrini, M Bzowski, R Demajistre, M A Dayeh, N A Schwadron, E R Christian, G Crew, P C FrischAbstract:The Interstellar Boundary Explorer (IBEX) observes a remarkable feature, the IBEX ribbon, which has energetic Neutral Atom (ENA) flux over a narrow region ~20° wide, a factor of 2-3 higher than the more globally distributed ENA flux. Here, we separate ENA emissions in the ribbon from the distributed flux by applying a transparency mask over the ribbon and regions of high emissions, and then solve for the distributed flux using an interpolation scheme. Our analysis shows that the energy spectrum and spatial distribution of the ribbon are distinct from the surrounding globally distributed flux. The ribbon energy spectrum shows a knee between ~1 and 4 keV, and the angular distribution is approximately independent of energy. In contrast, the distributed flux does not show a clear knee and more closely conforms to a power law over much of the sky. Consistent with previous analyses, the slope of the power law steepens from the nose to tail, suggesting a weaker termination shock toward the tail as compared to the nose. The knee in the energy spectrum of the ribbon suggests that its source plasma population is generated via a distinct physical process. Both the slope in the energy distribution of the distributed flux and the knee in the energy distribution of the ribbon are ordered by latitude. The heliotail may be identified in maps of globally distributed flux as a broad region of low flux centered ~44°W of the interstellar downwind direction, suggesting heliotail deflection by the interstellar magnetic field.
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The Interstellar Boundary Explorer High Energy (IBEX-Hi) Neutral Atom Imager
Space Science Reviews, 2009Co-Authors: H O Funsten, S A Fuselier, F Allegrini, P. Bochsler, G. Dunn, S. Ellis, D. Everett, M. J. Fagan, M. Granoff, M. GruntmanAbstract: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 to 6 keV and shares significant energy overlap and overall design philosophy with the IBEX-Lo 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° swath 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.
S A Fuselier - One of the best experts on this subject based on the ideXlab platform.
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heliospheric Neutral Atom spectra between 0 01 and 6 kev from ibex
The Astrophysical Journal, 2012Co-Authors: S A Fuselier, F Allegrini, M Bzowski, H O Funsten, A G Ghielmetti, G Gloeckler, D Heirtzler, P H JanzenAbstract: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 locationtolocationinthesky,includinginthedirectionoftheIBEXRibbon.Neutralfluxesareusedtoshowthatlow 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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exploring the time dispersion of the ibex hi energetic Neutral Atom spectra at the ecliptic poles
The Astrophysical Journal, 2012Co-Authors: S A Fuselier, F Allegrini, M Bzowski, H O Funsten, R Demajistre, M A Dayeh, M I DesaiAbstract:The Interstellar Boundary Explorer (IBEX) has observed energetic Neutral Atom (ENA) hydrogen emissions from the edge of the solar system for more than three years. The observations span energies from 0.01 to 6?keV FWHM. At energies greater than 0.5-6?keV, and for a travel distance of ~100?AU, the travel time difference between the slowest and the fastest ENA is more than a year. Therefore, we construct spectra including the effect that slower ENAs left the source at an earlier time than faster ones. If the source produces a steady rate of ENAs and the extinction does not vary, then we expect that the spectral shape would be time independent. However, while the extinction of ENAs has been fairly constant during the first two and a half years, the source appears to have changed, and thus the spectra at a single time may not represent the conditions at the source. IBEX's viewing allows continuous sampling of the ecliptic poles where fluxes can be continuously monitored. For a given source distance we construct spectra assuming that the measured ENAs left the source at roughly the same time. To accomplish this construction, we apply time lag corrections to the signal at different ENA energies that take into account the travel time difference. We show that the spectral shape at the poles exhibits a statistically significant change with time.
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Neutral Atom imaging of the magnetospheric cusps
Journal of Geophysical Research, 2011Co-Authors: S M Petrinec, D J Mccomas, S A Fuselier, H O Funsten, D Heirtzler, P H Janzen, M A Dayeh, H Kucharek, E MobiusAbstract:[1] The magnetospheric cusps separate closed dayside magnetospheric field lines from open field lines of the magnetotail mantle and lobes. All magnetospheric field lines that map to the magnetopause also pass through the cusp regions. Thus whenever magnetic reconnection occurs at the magnetopause, magnetosheath plasma can enter one or both of the cusp regions and charge exchange with the geocorona. The resulting energetic Neutral Atoms (ENAs) resulting from this charge exchange process propagate away from the cusps and are observed remotely by the Interstellar Boundary Explorer (IBEX). The asymmetry of the ENA intensities between the northern and southern cusps are strongly dependent upon the Earth's dipole tilt angle and are consistent with in situ cusp observations. These asymmetric fluxes in the cusp regions are suggested to be explained by the regions at the magnetopause where magnetic reconnection is expected.
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The Interstellar Boundary Explorer High Energy (IBEX-Hi) Neutral Atom Imager
Space Science Reviews, 2009Co-Authors: H O Funsten, S A Fuselier, F Allegrini, P. Bochsler, G. Dunn, S. Ellis, D. Everett, M. J. Fagan, M. Granoff, M. GruntmanAbstract: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 to 6 keV and shares significant energy overlap and overall design philosophy with the IBEX-Lo 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° swath 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.
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an unexplained 10 40 shift in the location of some diverse Neutral Atom data at 1 au
Advances in Space Research, 2004Co-Authors: M R Collier, Peter Wurz, T E Moore, S A Fuselier, D G Simpson, Aaron Roberts, A Szabo, Martin A Lee, B T TsurutaniAbstract:Abstract Four different data sets pertaining to the Neutral Atom environment at 1 AU are presented and discussed. These data sets include Neutral solar wind and interstellar Neutral Atom data from IMAGE/LENA, energetic hydrogen Atom data from SOHO/HSTOF and plasma wave data from the magnetometer on ISEE-3. Surprisingly, these data sets are centered between 262° and 292° ecliptic longitude, ∼10–40° from the upstream interstellar Neutral (ISN) flow direction at 254° resulting from the motion of the Sun relative to the local interstellar cloud (LIC). Some possible explanations for this offset, none of which is completely satisfactory, are discussed.
R Demajistre - One of the best experts on this subject based on the ideXlab platform.
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symmetry of the ibex ribbon of enhanced energetic Neutral Atom ena flux
The Astrophysical Journal, 2015Co-Authors: H O Funsten, J Heerikhuisen, M Bzowski, P H Janzen, R Demajistre, M A Dayeh, D M Cai, P C Frisch, Dave Higdon, B A LarsenAbstract:The circular ribbon of enhanced energetic Neutral Atom (ENA) emission observed by the Interstellar Boundary Explorer (IBEX) mission remains a critical signature for understanding the interaction between the heliosphere and the interstellar medium. We study the symmetry of the ribbon flux and find strong, spectrally dependent reflection symmetry throughout the energy range 0.7-4.3?keV. The distribution of ENA flux around the ribbon is predominantly unimodal at 0.7 and 1.1?keV, distinctly bimodal at 2.7 and 4.3?keV, and a mixture of both at 1.7?keV. The bimodal flux distribution consists of partially opposing bilateral flux lobes, located at highest and lowest heliographic latitude extents of the ribbon. The vector between the ribbon center and heliospheric nose (which defines the so-called BV plane) appears to play an organizing role in the spectral dependence of the symmetry axis locations as well as asymmetric contributions to the ribbon flux. The symmetry planes at 2.7 and 4.3?keV, derived by projecting the symmetry axes to a great circle in the sky, are equivalent to tilting the heliographic equatorial plane to the ribbon center, suggesting a global heliospheric ordering. The presence and energy dependence of symmetric unilateral and bilateral flux distributions suggest strong spectral filtration from processes encountered by an ion along its journey from the source plasma to its eventual detection at IBEX.
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circularity of the interstellar boundary explorer ribbon of enhanced energetic Neutral Atom ena flux
The Astrophysical Journal, 2013Co-Authors: H O Funsten, J Heerikhuisen, D J Mccomas, P H Janzen, R Demajistre, P C Frisch, B A Larsen, David Higdon, G LivadiotisAbstract:As a sharp feature in the sky, the ribbon of enhanced energetic Neutral Atom (ENA) flux observed by the Interstellar Boundary Explorer (IBEX) mission is a key signature for understanding the interaction of the heliosphere and the interstellar medium through which we are moving. Over five nominal IBEX energy passbands (0.7, 1.1, 1.7, 2.7, and 4.3 keV), the ribbon is extraordinarily circular, with a peak location centered at ecliptic (λRC, βRC) = (219.°2 ± 1.°3, 39.°9 ± 2.°3) and a half cone angle of C = 74.°5 ± 2.°0. A slight elongation of the ribbon, generally perpendicular to the ribbon center-heliospheric nose vector and with eccentricity ~0.3, is observed over all energies. At 4.3 keV, the ribbon is slightly larger and displaced relative to lower energies. For all ENA energies, a slice of the ribbon flux peak perpendicular to the circular arc is asymmetric and systematically skewed toward the ribbon center. We derive a spatial coherence parameter δC ≤ 0.014 that characterizes the spatial uniformity of the ribbon over its extent in the sky and is a key constraint for understanding the underlying processes and structure governing the ribbon ENA emission.
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exploring the time dispersion of the ibex hi energetic Neutral Atom spectra at the ecliptic poles
The Astrophysical Journal, 2012Co-Authors: S A Fuselier, F Allegrini, M Bzowski, H O Funsten, R Demajistre, M A Dayeh, M I DesaiAbstract:The Interstellar Boundary Explorer (IBEX) has observed energetic Neutral Atom (ENA) hydrogen emissions from the edge of the solar system for more than three years. The observations span energies from 0.01 to 6?keV FWHM. At energies greater than 0.5-6?keV, and for a travel distance of ~100?AU, the travel time difference between the slowest and the fastest ENA is more than a year. Therefore, we construct spectra including the effect that slower ENAs left the source at an earlier time than faster ones. If the source produces a steady rate of ENAs and the extinction does not vary, then we expect that the spectral shape would be time independent. However, while the extinction of ENAs has been fairly constant during the first two and a half years, the source appears to have changed, and thus the spectra at a single time may not represent the conditions at the source. IBEX's viewing allows continuous sampling of the ecliptic poles where fluxes can be continuously monitored. For a given source distance we construct spectra assuming that the measured ENAs left the source at roughly the same time. To accomplish this construction, we apply time lag corrections to the signal at different ENA energies that take into account the travel time difference. We show that the spectral shape at the poles exhibits a statistically significant change with time.
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separation of the interstellar boundary explorer ribbon from globally distributed energetic Neutral Atom flux
The Astrophysical Journal, 2011Co-Authors: F Allegrini, M Bzowski, R Demajistre, M A Dayeh, N A Schwadron, E R Christian, G Crew, P C FrischAbstract:The Interstellar Boundary Explorer (IBEX) observes a remarkable feature, the IBEX ribbon, which has energetic Neutral Atom (ENA) flux over a narrow region ~20° wide, a factor of 2-3 higher than the more globally distributed ENA flux. Here, we separate ENA emissions in the ribbon from the distributed flux by applying a transparency mask over the ribbon and regions of high emissions, and then solve for the distributed flux using an interpolation scheme. Our analysis shows that the energy spectrum and spatial distribution of the ribbon are distinct from the surrounding globally distributed flux. The ribbon energy spectrum shows a knee between ~1 and 4 keV, and the angular distribution is approximately independent of energy. In contrast, the distributed flux does not show a clear knee and more closely conforms to a power law over much of the sky. Consistent with previous analyses, the slope of the power law steepens from the nose to tail, suggesting a weaker termination shock toward the tail as compared to the nose. The knee in the energy spectrum of the ribbon suggests that its source plasma population is generated via a distinct physical process. Both the slope in the energy distribution of the distributed flux and the knee in the energy distribution of the ribbon are ordered by latitude. The heliotail may be identified in maps of globally distributed flux as a broad region of low flux centered ~44°W of the interstellar downwind direction, suggesting heliotail deflection by the interstellar magnetic field.
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The Two Wide-angle Imaging Neutral-Atom Spectrometers (TWINS) NASA Mission-of-Opportunity
Space Science Reviews, 2009Co-Authors: D J Mccomas, F Allegrini, J. Baldonado, B. Blake, P. C. Brandt, J. Burch, J. Clemmons, W. Crain, D. Delapp, R DemajistreAbstract:T wo W ide-angle I maging N eutral-Atom S pectrometers (TWINS) is a NASA Explorer Mission-of-Opportunity to stereoscopically image the Earth’s magnetosphere for the first time. TWINS extends our understanding of magnetospheric structure and processes by providing simultaneous Energetic Neutral Atom (ENA) imaging from two widely separated locations. TWINS observes ENAs from 1–100 keV with high angular (∼4°×4°) and time (∼1-minute) resolution. The TWINS Ly- α monitor measures the geocoronal hydrogen density to aid in ENA analysis while environmental sensors provide contemporaneous measurements of the local charged particle environments. By imaging ENAs with identical instruments from two widely spaced, high-altitude, high-inclination spacecraft, TWINS enables three-dimensional visualization of the large-scale structures and dynamics within the magnetosphere for the first time. This “instrument paper” documents the TWINS design, construction, calibration, and initial results. Finally, the appendix of this paper describes and documents the Southwest Research Institute (SwRI) instrument calibration facility; this facility was used for all TWINS instrument-level calibrations.
