E. Moebius

University of Montana, Missoula, Montana, United States

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Publications (500)1323.91 Total impact

  • [Show abstract] [Hide abstract] ABSTRACT: We present an improved analysis of the energy spectrum of energetic neutral hydrogen from the heliosheath observed with the IBEX-Lo sensor on the Interstellar Boundary EXplorer from the years 2009 to 2012. This analysis allows us to study the lowest energies between 10 and 100 eV although various background sources are more intense than the targeted signal over broad areas of the sky. The results improve our knowledge of the interaction region between our heliosphere and the interstellar plasma because these neutral atoms are direct messengers from the low-energy plasma in the heliosheath. We find a roll-over of the energy spectrum below 100 eV, which has major implications for the pressure balance of the plasma in the inner heliosheath. The results can also be compared directly with in situ observations of the Voyager 1 and 2 spacecraft.
    No preview · Article · Apr 2016 · The Astrophysical Journal
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    [Show abstract] [Hide abstract] ABSTRACT: With the velocity vector and temperature of the pristine interstellar neutral (ISN) He recently obtained with high precision from a coordinated analysis summarized by McComas et al.2015b, we analyzed the IBEX observations of neutral He left out from this analysis. These observations were collected during the ISN observation seasons 2010---2014 and cover the region in the Earth's orbit where the Warm Breeze persists. We used the same simulation model and a very similar parameter fitting method to that used for the analysis of ISN He. We approximated the parent population of the Warm Breeze in front of the heliosphere with a homogeneous Maxwell-Boltzmann distribution function and found a temperature of $\sim 9\,500$ K, an inflow speed of 11.3 km s$^{-1}$, and an inflow longitude and latitude in the J2000 ecliptic coordinates $251.6^\circ$, $12.0^\circ$. The abundance of the Warm Breeze relative to the interstellar neutral He is 5.7\% and the Mach number is 1.97. The newly found inflow direction of the Warm Breeze, the inflow directions of ISN H and ISN He, and the direction to the center of IBEX Ribbon are almost perfectly co-planar, and this plane coincides within relatively narrow statistical uncertainties with the plane fitted only to the inflow directions of ISN He, ISN H, and the Warm Breeze. This co-planarity lends support to the hypothesis that the Warm Breeze is the secondary population of ISN He and that the center of the Ribbon coincides with the direction of the local interstellar magnetic field. The common plane for the direction of inflow of ISN gas, ISN H, the Warm Breeze, and the local interstellar magnetic field %includes the Sun and is given by the normal direction: ecliptic longitude $349.7^\circ \pm 0.6^\circ$ and latitude $35.7^\circ \pm 0.6^\circ$ in the J2000 coordinates, with the correlation coefficient of 0.85.
    Full-text · Article · Apr 2016 · The Astrophysical Journal Supplement Series
  • Eberhard Möbius · Martin A. Lee · Christian Drews · George Gloeckler
    [Show abstract] [Hide abstract] ABSTRACT: The precise interstellar neutral (ISN) flow direction is important because of its strong leverage on the plane subtended by the ISN and magnetic field vectors, which controls the heliospheric shape and interaction with the interstellar medium. IBEX measurements provide a very precise relation between ISN flow longitude and speed via the hyperbolic trajectory equation, forming a 4-dimensional tube in the ISN parameter space, with substantially larger uncertainty along this tube and thus for the longitude alone. As demonstrated before, the interstellar pickup ion (PUI) cut-off speed is a function of the ratio of the radial ISN flow component and the solar wind speed at the observer location. The former is largest precisely upwind and decreases symmetrically with the angle from the upwind direction. Using this functional dependence and the observed solar wind speed, the PUI cut-off can be constructed solely as a function of the ISN flow longitude. From ACE SWICS and STEREO PLASTIC, data sets that span 18+ years are available. We will show, in particular, that by selecting observations for local interplanetary magnetic fields perpendicular to the solar wind and transforming the observed distributions into the solar wind frame, a comparison with data can be devised that is much less sensitive to PUI production and transport effects than methods that rely on pickup ion fluxes.
    No preview · Conference Paper · Mar 2016
  • [Show abstract] [Hide abstract] ABSTRACT: Since launch in Oct. 2008, IBEX, with its two energetic neutral atom (ENA) cameras, has provided humankind with the first-ever global images of the complex boundary separating the heliosphere from the local interstellar medium (LISM). IBEX’s energy-resolved all-sky maps, collected every six months, are yielding remarkable new insights into the heliospheres structure as it is shaped by the combined forces of the local interstellar flow, the local interstellar magnetic field (LISMF), and the evolving solar wind. IBEX has also acquired the first images of ENAs backscattered from the surface of the moon as well as global images of the magnetospheric response to solar wind disturbances. IBEX thus addresses all three Heliophysics science objectives set forth in the 2014 Science Plan for NASAs Science Mission Directorate (SMD) as well as the goals in the recent Solar and Space Physics Decadal Survey (NRC 2012). In addition, with the information it provides on the properties of the LISM and the LISMF, IBEX represents a unique bridge between heliophysics and astrophysics, and fills in critical knowledge for understanding the habitability of exoplanetary systems and the future habitability of Earth and the solar system. Because of the few-year time lag due to solar wind and ENA transport, IBEX observed the solar wind/ LISM interaction characteristic of declining phase/solar minimum conditions. In the continuing mission, IBEX captures the response of the interstellar boundaries to the changing structure of the solar wind in its transition toward the “mini” solar maximum and possibly the decline into the next solar minimum. The continuing IBEX mission affords never-to-be-repeated opportunities to coordinate global imaging of the heliospheric boundary with in-situ measurements by the Voyagers as they pass beyond the heliopause and start to directly sample the LISM.
    No preview · Article · Mar 2016
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    [Show abstract] [Hide abstract] ABSTRACT: We simulated the modulation of the interstellar neutral (ISN) He, Ne, and O density and pick-up ion (PUI) production rate and count rate along the Earth's orbit over the solar cycle from 2002 to 2013 to verify if solar cycle-related effects may modify the inferred ecliptic longitude of the ISN inflow direction. We adopted the classical PUI model with isotropic distribution function and adiabatic cooling, modified by time- and heliolatitude-dependent ionization rates and non-zero injection speed of PUIs. We found that the ionization losses have a noticeable effect on the derivation of the ISN inflow longitude based on the Gaussian fit to the crescent and cone peak locations. We conclude that the non-zero radial velocity of the ISN flow and the energy range of the PUI distribution function that is accumulated are of importance for a precise reproduction of the PUI count rate along the Earth orbit. However, the temporal and latitudinal variations of the ionization in the heliosphere, and particularly their variation on the solar cycle time scale, may significantly modify the shape of PUI cone and crescent and also their peak positions from year to year and thus bias by a few degrees the derived longitude of the ISN gas inflow direction.
    Preview · Article · Mar 2016 · Monthly Notices of the Royal Astronomical Society
  • E. Möbius · M. A. Lee · C. Drews
    [Show abstract] [Hide abstract] ABSTRACT: We provide a proof of concept that the pickup ion (PUI) cutoff speed variation with ecliptic longitude can provide the interstellar neutral (ISN) flow longitude outside the heliosphere with a precision of the order of 01. We compare 2007–2014 STEREO A PLASTIC observations in the solar wind frame with a simple analytical cutoff model and perform a Pearson correlation of the cutoff as a function of longitude with those values mirrored about a location λM that slides in longitude. The resulting maximum correlation at λM = 25521 ± 004 reflects the ISN upwind direction with a purely statistical uncertainty. This result is consistent with recent ISN flow longitude values, but a precision determination requires the evaluation of underlying systematic effects. Obtaining a precision ISN flow longitude is highly complementary to the IBEX ISN observations, which return a narrow tube in the ISN parameter space that couples flow speed and longitude tightly, but leaves a substantially larger error bar along the tube. The ISN flow provides one cardinal axis of the heliosphere, with a strong leverage on the plane subtended by the ISN velocity and the interstellar magnetic field vector, which controls the shape of the heliosphere and its interaction with the interstellar medium. In addition, a discussion about potential temporal variations of the ISN flow has started. Both issues require a precision determination of the ISN flow velocity over decade-long time intervals. ACE SWICS, STEREO PLASTIC, and SOHO CTOF PUI data allow such long-term studies over almost two decades.
    No preview · Article · Dec 2015 · The Astrophysical Journal
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    [Show abstract] [Hide abstract] ABSTRACT: Determining the direction of the local interstellar magnetic field (LISMF) is important for understanding the heliosphere's global structure, the properties of the interstellar medium, and the propagation of cosmic rays in the local galactic medium. Measurements of interstellar neutral atoms by Ulysses for He and by SOHO/SWAN for H provided some of the first observational insights into the LISMF direction. Because secondary neutral H is partially deflected by the interstellar flow in the outer heliosheath and this deflection is influenced by the LISMF, the relative deflection of H versus He provides a plane - the so-called B-V plane in which the LISMF direction should lie. Interstellar Boundary Explorer (IBEX) subsequently discovered a ribbon, the center of which is conjectured to be the LISMF direction. The most recent He velocity measurements from IBEX and those from Ulysses yield a B-V plane with uncertainty limits that contain the centers of the IBEX ribbon at 0.7-2.7 keV. The possibility that Voyager 1 has moved into the outer heliosheath now suggests that Voyager 1's direct observations provide another independent determination of the LISMF. We show that LISMF direction measured by Voyager 1 is >40.
    Preview · Article · Oct 2015
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    [Show abstract] [Hide abstract] ABSTRACT: This paper is one of three companion papers presenting the results of our in-depth analysis of the interstellar neutral helium (ISN He) observations carried out using the IBEX-Lo during the first six Interstellar Boundary Explorer (IBEX) observation seasons. We derive corrections for losses due to the limited throughput of the interface buffer and determine the IBEX spin-axis pointing. We develop an uncertainty system for the data, taking into account the resulting correlations between the data points. This system includes uncertainties due to Poisson statistics, background, spin-axis determination, systematic deviation of the boresight from the prescribed position, correction for the interface buffer losses, and the expected Warm Breeze (WB) signal. Subsequently, we analyze the data from 2009 to examine the role of various components of the uncertainty system. We show that the ISN He flow parameters are in good agreement with the values obtained by the original analysis. We identify the WB as the principal contributor to the global $\chi^2$ values in previous analyses. Other uncertainties have a much milder role and their contributions are comparable to each other. The application of this uncertainty system reduced the minimum $\chi^2$ value 4-fold. The obtained $\chi^2$ value, still exceeding the expected value, suggests that either the uncertainty system may still be incomplete or the adopted physical model lacks a potentially important element, which is likely an imperfect determination of the WB parameters. The derived corrections and uncertainty system are used in the accompanying paper by Bzowski et al. in an analysis of the data from six seasons.
    Full-text · Article · Oct 2015 · The Astrophysical Journal Supplement Series
  • Martin A. Lee · Eberhard Möbius · Trevor W. Leonard
    [Show abstract] [Hide abstract] ABSTRACT: A new analytical model based on the previous work of Lee et al. is presented for the distribution of interstellar helium in the heliosphere. The model is tailored for comparison with the IBEX-Lo observations in order to determine the bulk velocity and temperature of helium in the local interstellar cloud. The model includes solar gravity, spherically symmetric stationary ionization rates, transformation to the Earth/IBEX frame of reference, the IBEX viewing geometry with small spin-axis tilt, and integration of the atom differential intensity over energy and the instrument collimator solid angle. The analysis employs an expansion of the count rate about the peak of the velocity distribution to second order in the magnitudes of several small quantities: the ratio of the helium thermal speed to its bulk speed, the angle between the bulk velocity and the ecliptic, the two angles describing the tilt of the IBEX spin-axis away from Sun-pointing, the collimator angular width, and the angular difference between the observing longitude and the longitude where the projection of the bulk velocity onto the ecliptic is tangential to Earth's orbit. The model reveals the evolving ellipsoidal shape of the helium distribution as it moves along its average hyperbolic orbit. For specified interstellar parameters, the model predicts the latitudinal and longitudinal structure of the helium distribution. The model is in reasonable agreement with IBEX observations and the predictions of the other available models. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Oct 2015 · The Astrophysical Journal Supplement Series
  • [Show abstract] [Hide abstract] ABSTRACT: To better constrain the parameters of the interstellar neutral flow, we searched the Interstellar Boundary EXplorer (IBEX)-Lo database for helium and oxygen from the interstellar medium in the anti-ram direction in the three years (2009-2011) with the lowest background rates. We found that IBEX-Lo cannot observe interstellar helium from the anti-ram direction because the helium energy is too low for indirect detection by sputtering off the IBEX-Lo conversion surface. Our results show that this sputtering process has a low energy threshold between 25 and 30 eV, whereas the energy of the incident helium is only 10 eV for these observations. Interstellar oxygen, on the other hand, could in principle be detected in the anti-ram hemisphere, but the expected magnitude of the signal is close to the detection limit imposed by counting statistics and by the magnetospheric foreground. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Oct 2015 · The Astrophysical Journal Supplement Series
  • [Show abstract] [Hide abstract] ABSTRACT: We investigate the directional distribution of heavy neutral atoms in the heliosphere by using heavy neutral maps generated with the IBEX-Lo instrument over three years from 2009 to 2011. The interstellar neutral (ISN) O&Ne gas flow was found in the first-year heavy neutral map at 601 keV and its flow direction and temperature were studied. However, due to the low counting statistics, researchers have not treated the full sky maps in detail. The main goal of this study is to evaluate the statistical significance of each pixel in the heavy neutral maps to get a better understanding of the directional distribution of heavy neutral atoms in the heliosphere. Here, we examine three statistical analysis methods: the signal-to-noise filter, the confidence limit method, and the cluster analysis method. These methods allow us to exclude background from areas where the heavy neutral signal is statistically significant. These methods also allow the consistent detection of heavy neutral atom structures. The main emission feature expands toward lower longitude and higher latitude from the observational peak of the ISN O&Ne gas flow. We call this emission the extended tail. It may be an imprint of the secondary oxygen atoms generated by charge exchange between ISN hydrogen atoms and oxygen ions in the outer heliosheath. © 2015. The American Astronomical Society. All rights reserved..
    No preview · Article · Oct 2015 · The Astrophysical Journal Supplement Series
  • [Show abstract] [Hide abstract] ABSTRACT: Measurements of energetic neutral atoms (ENAs) have been extremely successful in providing very important information on the physical processes inside and outside of our heliosphere. For instance, recent Interstellar Boundary Explorer (IBEX) observations have provided new insights into the local interstellar environment and improved measurements of the interstellar He temperature, velocity, and direction of the interstellar flow vector. Since particle collisions are rare, and radiation pressure is negligible for these neutrals, gravitational forces mainly determine the trajectories of neutral He atoms. Depending on the distance of an ENA to the source of a gravitational field and its relative speed and direction, this can result in significant deflection and acceleration. In this paper, we investigate the impact of the gravitational effects of Earth, the Moon, and Jupiter on ENA measurements performed in Earth's orbit. The results show that current analysis of the interstellar neutral parameters by IBEX is not significantly affected by planetary gravitational effects. We further studied the possibility of whether or not the Helium focusing cone of the Sun and Jupiter could be measured by IBEX and whether or not these cones could be used as an independent measure of the temperature of interstellar Helium. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Oct 2015 · The Astrophysical Journal Supplement Series
  • [Show abstract] [Hide abstract] ABSTRACT: We explore the possibility that interstellar O and Ne may be contributing to the particle signal from the GAS instrument on Ulysses, which is generally assumed to be entirely He. Motivating this study is the recognition that an interstellar temperature higher than any previously estimated from Ulysses data could potentially resolve a discrepancy between Ulysses He measurements and those from the Interstellar Boundary Explorer (IBEX). Contamination by O and Ne could lead to Ulysses temperature measurements that are too low. We estimate the degree of O and Ne contamination necessary to increase the inferred Ulysses temperature to 8500 K, which would be consistent with both the Ulysses and IBEX data given the same interstellar flow speed. We find that producing the desired effect requires a heavy element contamination level of ∼9% of the total Ulysses/GAS signal. However, this degree of heavy element contribution is about an order of magnitude higher than expected based on our best estimates of detection efficiencies, ISM abundances, and heliospheric survival probabilities, making it unlikely that heavy element contamination is significantly affecting temperatures derived from Ulysses data. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Oct 2015 · The Astrophysical Journal Supplement Series
  • [Show abstract] [Hide abstract] ABSTRACT: The Interstellar Boundary Explorer (IBEX) has been directly observing neutral atoms from the local interstellar medium for the last six years (2009-2014). This paper ties together the 14 studies in this Astrophysical Journal Supplement Series Special Issue, which collectively describe the IBEX interstellar neutral results from this epoch and provide a number of other relevant theoretical and observational results. Interstellar neutrals interact with each other and with the ionized portion of the interstellar population in the "pristine" interstellar medium ahead of the heliosphere. Then, in the heliosphere's close vicinity, the interstellar medium begins to interact with escaping heliospheric neutrals. In this study, we compare the results from two major analysis approaches led by IBEX groups in New Hampshire and Warsaw. We also directly address the question of the distance upstream to the pristine interstellar medium and adjust both sets of results to a common distance of ∼1000 AU. The two analysis approaches are quite different, but yield fully consistent measurements of the interstellar He flow properties, further validating our findings. While detailed error bars are given for both approaches, we recommend that for most purposes, the community use "working values" of ∼25.4 km s-1, ∼75.°7 ecliptic inflow longitude, ∼ -5.°1 ecliptic inflow latitude, and ∼7500 K temperature at ∼1000 AU upstream. Finally, we briefly address future opportunities for even better interstellar neutral observations to be provided by the Interstellar Mapping and Acceleration Probe mission, which was recommended as the next major Heliophysics mission by the NRC's 2013 Decadal Survey. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Oct 2015 · The Astrophysical Journal Supplement Series
  • [Show abstract] [Hide abstract] ABSTRACT: The Interstellar Boundary Explorer (IBEX) samples the interstellar neutral (ISN) gas flow of several species every year from December through late March when the Earth moves into the incoming flow. The first quantitative analyses of these data resulted in a narrow tube in four-dimensional interstellar parameter space, which couples speed, flow latitude, flow longitude, and temperature, and center values with approximately 3° larger longitude and 3 km s-1 lower speed, but with temperatures similar to those obtained from observations by the Ulysses spacecraft. IBEX has now recorded six years of ISN flow observations, providing a large database over increasing solar activity and using varying viewing strategies. In this paper, we evaluate systematic effects that are important for the ISN flow vector and temperature determination. We find that all models in use return ISN parameters well within the observational uncertainties and that the derived ISN flow direction is resilient against uncertainties in the ionization rate. We establish observationally an effective IBEX-Lo pointing uncertainty of ±0.°18 in spin angle and confirm an uncertainty of ±0.°1 in longitude. We also show that the IBEX viewing strategy with different spin-axis orientations minimizes the impact of several systematic uncertainties, and thus improves the robustness of the measurement. The Helium Warm Breeze has likely contributed substantially to the somewhat different center values of the ISN flow vector. By separating the flow vector and temperature determination, we can mitigate these effects on the analysis, which returns an ISN flow vector very close to the Ulysses results, but with a substantially higher temperature. Due to coupling with the ISN flow speed along the ISN parameter tube, we provide the temperature K for for comparison, where most of the uncertainty is systematic and likely due to the presence of the Warm Breeze. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Oct 2015 · The Astrophysical Journal Supplement Series
  • [Show abstract] [Hide abstract] ABSTRACT: Interstellar He represents a key sample of interstellar matter that, due to its high first ionization potential, survives the journey from beyond our solar system's heliospheric boundaries to Earth. Ongoing analysis of interstellar neutral (ISN) He atoms by the Interstellar Boundary Explorer (IBEX) has resulted in a growing sophistication in our understanding of the local interstellar flow. A key feature of the IBEX observations near perihelion of the ISN trajectories is a narrow "tube" of approximately degenerate interstellar parameters. These degenerate solutions provide a tightly coupled relationship between the interstellar flow longitude and latitude, speed, and temperature. However, the IBEX analysis resulting in a specific solution for the inflow longitude, inflow speed, temperature, and inflow latitude was accompanied by a sizeable uncertainty along the parameter tube. Here, we use the three-step method to find the interstellar parameters: (1) the ISN He peak rate in ecliptic longitude uniquely determines a relation (as part of the tube in parameter space) between the longitude and the speed of the He ISN flow at infinity; (2) the ISN He peak latitude (on the great circle swept out in each spin) is compared to simulations to derive unique values for and along the parameter tube; and (3) the angular width of the He flow distributions as a function of latitude is used to derive the interstellar He temperature. For simulated peak latitudes, we use a relatively new analytical tool that traces He atoms from beyond the termination shock into the position of IBEX and incorporates the detailed response function of IBEX-Lo. By varying the interstellar parameters along the IBEX parameter tube, we find the specific parameters that minimize the chi-square difference between observations and simulations. The new computational tool for simulating neutral atoms through the integrated IBEX-Lo response function makes no assumptions or expansions with respect to the spin-axis pointing or frame of reference. Thus, we are able to move beyond closed-form approximations and utilize observations of interstellar He during the complete five year period from 2009 to 2013 when the primary component of interstellar He is most prominent. Chi-square minimization of simulations compared to observations results in a He ISN flow longitude of 75.°6 ± 1.°4, latitude of -5.°12 ± 0.°27, speed of 25.4 ± 1.1 km s-1, and temperature of 8000 ± 1300 K, where the uncertainties are related and apply along the IBEX parameter tube. This paper also provides documentation for a new release of ISN data and associated model runs. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Oct 2015 · The Astrophysical Journal Supplement Series
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    [Show abstract] [Hide abstract] ABSTRACT: We analyzed observations of interstellar neutral helium (ISN~He) obtained from the Interstellar Boundary Explorer (IBEX) satellite during its first six years of operation. We used a refined version of the ISN~He simulation model, presented in the companion paper by Sokol_et al. 2015, and a sophisticated data correlation and uncertainty system and parameter fitting method, described in the companion paper by Swaczyna et al 2015. We analyzed the entire data set together and the yearly subsets, and found the temperature and velocity vector of ISN~He in front of the heliosphere. As seen in the previous studies, the allowable parameters are highly correlated and form a four-dimensional tube in the parameter space. The inflow longitudes obtained from the yearly data subsets show a spread of ~6 degree, with the other parameters varying accordingly along the parameter tube, and the minimum chi-square value is larger than expected. We found, however, that the Mach number of the ISN~He flow shows very little scatter and is thus very tightly constrained. It is in excellent agreement with the original analysis of ISN~He observations from IBEX and recent reanalyses of observations from Ulysses. We identify a possible inaccuracy in the Warm Breeze parameters as the likely cause of the scatter in the ISN~He parameters obtained from the yearly subsets, and we suppose that another component may exist in the signal, or a process that is not accounted for in the current physical model of ISN~He in front of the heliosphere. From our analysis, the inflow velocity vector, temperature, and Mach number of the flow are equal to lambda_ISNHe = 255.8 +/- 0.5 degree, beta_ISNHe = 5.16 +/- 0.10 degree, T_ISNHe = 7440 +/- 260 K, v_ISNHe = 25.8 +/- 0.4$ km/s, and M_ISNHe = 5.079 +/- 0.028, with uncertainties strongly correlated along the parameter tube.
    Full-text · Article · Oct 2015 · The Astrophysical Journal Supplement Series
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    [Show abstract] [Hide abstract] ABSTRACT: Neutral interstellar helium has been observed by the Interstellar Boundary Explorer (IBEX) since 2009 with a signal-to-noise ratio well above 1000. Because of the geometry of the observations, the signal observed from January to March each year is the easiest to identify. However, as we show via simulations, the portion of the signal in the range of intensities from 10^{-3} to 10^{-2} of the peak value, previously mostly left out from the analysis, may bring important information about the details of the distribution function of interstellar He gas in front of the heliosphere. In particular, these observations may inform us about possible departures of the parent interstellar He population from equilibrium. We compare the expected distribution of the signal for the canonical assumption of a single Maxwell-Boltzmann population with the distributions for a superposition of the Maxwell-Boltzmann primary population and the recently discovered Warm Breeze, and for a single primary population given by a kappa function. We identify the regions on the sky where the differences between those cases are expected to be the most visible against the background. We discuss the diagnostic potential of the fall peak of the interstellar signal, reduced by a factor of 50 due to the Compton-Getting effect but still above the detection limit of IBEX. We point out the strong energy dependence of the fall signal and suggest that searching for this signal in the data could bring an independent assessment of the low-energy measurement threshold of the IBEX-Lo sensor.
    Full-text · Article · Oct 2015 · The Astrophysical Journal Supplement Series
  • [Show abstract] [Hide abstract] ABSTRACT: The Interstellar Boundary Explorer (IBEX) observes enhanced ~ keV energy Energetic Neutral Atoms (ENAs) from a narrow "ribbon" that stretches across the sky and appears to be centered on the direction of the local interstellar magnetic field. The Milagro collaboration, the Asγ collaboration and the IceCube observatory have made global maps of TeV cosmic rays. This paper provides links between these disparate observations. We develop a simple diffusive model of the propagation of cosmic rays and the associated cosmic ray anisotropy due to cosmic ray streaming against the local interstellar flow. We show that the local plasma and field conditions sampled by IBEX provide characteristics that consistently explain TeV cosmic ray anisotropies. These results support models that place the interstellar magnetic field direction near the center of the IBEX ribbon.
    No preview · Article · Sep 2015
  • J. H. Chen · N. A. Schwadron · E. Möbius · M. Gorby
    [Show abstract] [Hide abstract] ABSTRACT: We present a modeling study of interstellar pickup ion (PUI) distributions in co-rotating interaction regions (CIRs). We consider gradual compressions associated with CIRs formed when fast speed streams overtake slower streams in the inner heliosphere. For the analysis, we adopt a simplified magnetohydrodynamic model of a CIR [Giacalone et al., 2002]. The Energetic Particle Radiation Environment Module (EPREM) [Schwadron et al., 2010], a parallelized particle numerical kinetic code, is used to model PUI distributions using the focused transport equation, including adiabatic cooling/heating, adiabatic focusing, and parallel and perpendicular diffusion. The continuous injection of PUIs is handled as a source term with a ring distribution in velocity space that is produced from the local neutral density obtained from a hot model of the interstellar neutral gas. The simulated distributions exhibit a harder spectrum in the compression region and a softer spectrum in the rarefaction region than that in undisturbed solar wind. As an additional result, a v−5 power-law tail distribution above the PUI cut-off speed (a knee in the distribution) emerges for a particular velocity gradient in the CIR. The tail above the PUI cut-off is sensitive to the CIR velocity gradient, and in one observational case studied, this relationship adequately explains the observed spectrum from 2 to 4 times the solar wind speed. This suggests that the velocity gradient associated with the CIR formation can efficiently create a seed population of PUIs before a shock forms even without stochastic acceleration. Thus, local CIR compressions without shocks may play a significant role in the acceleration process as suggested previously [e.g., Chotoo et al., 2001; Giacalone et al., 2002; Ebert et al., 2012].
    No preview · Article · Sep 2015 · Journal of Geophysical Research: Space Physics

Publication Stats

9k Citations
1,323.91 Total Impact Points

Institutions

  • 2014
    • University of Montana
      • Department of Physics and Astronomy
      Missoula, Montana, United States
  • 2013
    • Los Alamos National Laboratory
      Лос-Аламос, California, United States
    • University of Texas at San Antonio
      • Department of Physics and Astronomy
      San Antonio, Texas, United States
  • 1-2011
    • University of New Hampshire
      • • Space Science Center
      • • Institute for the Study of Earth, Oceans, and Space
      Durham, NH, United States
  • 2010
    • Christian-Albrechts-Universität zu Kiel
      • Institute of Experimental and Applied Physics (IEAP)
      Kiel, Schleswig-Holstein, Germany
  • 2002
    • Rikkyo University
      • Department of Physics
      Edo, Tōkyō, Japan
  • 1999
    • University of California, Berkeley
      Berkeley, California, United States
    • Durham University
      Durham, England, United Kingdom
  • 1998
    • The University of Arizona
      • Department of Physics
      Tucson, Arizona, United States
    • Technische Universität Braunschweig
      Brunswyck, Lower Saxony, Germany
  • 1986-1991
    • Max Planck Institute for Extraterrestrial Physics
      Arching, Bavaria, Germany
  • 1986-1990
    • Loyola University Maryland
      Baltimore, Maryland, United States
  • 1986-1987
    • University of Maryland, College Park
      • Department of Physics
      CGS, Maryland, United States