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Title: Seven Years of Imaging the Global Heliosphere with IBEX

Abstract

The Interstellar Boundary Explorer ( IBEX ) has now operated in space for 7 years and returned nearly continuous observations that have led to scientific discoveries and reshaped our entire understanding of the outer heliosphere and its interaction with the local interstellar medium. Here we extend prior work, adding the 2014–2015 data for the first time, and examine, validate, initially analyze, and provide a complete 7-year set of Energetic Neutral Atom (ENA) observations from ∼0.1 to 6 keV. The data, maps, and documentation provided here represent the 10th major release of IBEX data and include improvements to various prior corrections to provide the citable reference for the current version of IBEX data. We are now able to study time variations in the outer heliosphere and interstellar interaction over more than half a solar cycle. We find that the Ribbon has evolved differently than the globally distributed flux (GDF), with a leveling off and partial recovery of ENAs from the GDF, owing to solar wind output flattening and recovery. The Ribbon has now also lost its latitudinal ordering, which reflects the breakdown of solar minimum solar wind conditions and exhibits a greater time delay than for the surrounding GDF. Together, themore » IBEX observations strongly support a secondary ENA source for the Ribbon, and we suggest that this be adopted as the nominal explanation of the Ribbon going forward.« less

Authors:
;  [1]; ; ;  [2]; ; ;  [3];  [4]; ;  [5]; ; ;  [6];  [7]
  1. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
  2. Space Research Centre of the Polish Academy of Sciences, Bartycka 18A, 00-716, Warsaw (Poland)
  3. Southwest Research Institute, P.O. Drawer 28510, San Antonio, TX 78228 (United States)
  4. Los Alamos National Laboratory, Intelligence and Space Research Division, P.O. Box 1663, Los Alamos, NM 87545 (United States)
  5. University of Montana, 32 Campus Drive, Missoula, MT 59812 (United States)
  6. University of New Hampshire, Space Science Center, Morse Hall Rm 407, Durham, NH 03824 (United States)
  7. Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601 (Japan)
Publication Date:
OSTI Identifier:
22661132
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal, Supplement Series; Journal Volume: 229; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ATOMS; CORRECTIONS; HELIOSPHERE; INTERSTELLAR SPACE; MAGNETIC FIELDS; SOLAR CYCLE; SOLAR WIND; SPACE; SUN; TIME DELAY; VARIATIONS

Citation Formats

McComas, D. J., Zirnstein, E. J., Bzowski, M., Kubiak, M. A., Sokół, J. M., Dayeh, M. A., Fuselier, S. A., Szalay, J. R., Funsten, H. O., Janzen, P. H., Reisenfeld, D. B., Kucharek, H., Möbius, E., Schwadron, N. A., and Tokumaru, M., E-mail: dmccomas@princeton.edu. Seven Years of Imaging the Global Heliosphere with IBEX. United States: N. p., 2017. Web. doi:10.3847/1538-4365/AA66D8.
McComas, D. J., Zirnstein, E. J., Bzowski, M., Kubiak, M. A., Sokół, J. M., Dayeh, M. A., Fuselier, S. A., Szalay, J. R., Funsten, H. O., Janzen, P. H., Reisenfeld, D. B., Kucharek, H., Möbius, E., Schwadron, N. A., & Tokumaru, M., E-mail: dmccomas@princeton.edu. Seven Years of Imaging the Global Heliosphere with IBEX. United States. doi:10.3847/1538-4365/AA66D8.
McComas, D. J., Zirnstein, E. J., Bzowski, M., Kubiak, M. A., Sokół, J. M., Dayeh, M. A., Fuselier, S. A., Szalay, J. R., Funsten, H. O., Janzen, P. H., Reisenfeld, D. B., Kucharek, H., Möbius, E., Schwadron, N. A., and Tokumaru, M., E-mail: dmccomas@princeton.edu. Sat . "Seven Years of Imaging the Global Heliosphere with IBEX". United States. doi:10.3847/1538-4365/AA66D8.
@article{osti_22661132,
title = {Seven Years of Imaging the Global Heliosphere with IBEX},
author = {McComas, D. J. and Zirnstein, E. J. and Bzowski, M. and Kubiak, M. A. and Sokół, J. M. and Dayeh, M. A. and Fuselier, S. A. and Szalay, J. R. and Funsten, H. O. and Janzen, P. H. and Reisenfeld, D. B. and Kucharek, H. and Möbius, E. and Schwadron, N. A. and Tokumaru, M., E-mail: dmccomas@princeton.edu},
abstractNote = {The Interstellar Boundary Explorer ( IBEX ) has now operated in space for 7 years and returned nearly continuous observations that have led to scientific discoveries and reshaped our entire understanding of the outer heliosphere and its interaction with the local interstellar medium. Here we extend prior work, adding the 2014–2015 data for the first time, and examine, validate, initially analyze, and provide a complete 7-year set of Energetic Neutral Atom (ENA) observations from ∼0.1 to 6 keV. The data, maps, and documentation provided here represent the 10th major release of IBEX data and include improvements to various prior corrections to provide the citable reference for the current version of IBEX data. We are now able to study time variations in the outer heliosphere and interstellar interaction over more than half a solar cycle. We find that the Ribbon has evolved differently than the globally distributed flux (GDF), with a leveling off and partial recovery of ENAs from the GDF, owing to solar wind output flattening and recovery. The Ribbon has now also lost its latitudinal ordering, which reflects the breakdown of solar minimum solar wind conditions and exhibits a greater time delay than for the surrounding GDF. Together, the IBEX observations strongly support a secondary ENA source for the Ribbon, and we suggest that this be adopted as the nominal explanation of the Ribbon going forward.},
doi = {10.3847/1538-4365/AA66D8},
journal = {Astrophysical Journal, Supplement Series},
number = 2,
volume = 229,
place = {United States},
year = {Sat Apr 01 00:00:00 EDT 2017},
month = {Sat Apr 01 00:00:00 EDT 2017}
}
  • We present a comprehensive study of energetic neutral atoms (ENAs) of 10 eV to 2.5 keV from the downwind hemisphere of the heliosphere. These ENAs are believed to originate mostly from pickup protons and solar wind protons in the inner heliosheath. This study includes all low-energy observations made with the Interstellar Boundary Explorer over the first 8 years. Since the protons around 0.1 keV dominate the plasma pressure in the inner heliosheath in downwind direction, these ENA observations offer the unique opportunity to constrain the plasma properties and dimensions of the heliosheath where no in-situ observations are available. We firstmore » derive energy spectra of ENA intensities averaged over time for 49 macropixels covering the entire downwind hemisphere. The results confirm previous studies regarding integral intensities and the roll-over around 0.1 keV energy. With the expanded dataset we now find that ENA intensities at 0.2 and 0.1 keV seem to anti-correlate with solar activity. We then derive the product of total plasma pressure and emission thickness of protons in the heliosheath to estimate lower limits on the thickness of the inner heliosheath. The temporally averaged ENA intensities support a rather spherical shape of the termination shock and a heliosheath thickness between 150 and 210 au for most regions of the downwind hemisphere. Around the nominal downwind direction of 76° ecliptic longitude, the heliosheath is at least 280 au thick. There, the neutral hydrogen density seems to be depleted compared to upwind directions by roughly a factor of 2.« less
  • 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 magnetosphericmore » 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.« less
  • The brightest and most surprising feature in the first all-sky maps of energetic neutral atom (ENA) emissions (0.2-6 keV) produced by the Interstellar Boundary Explorer (IBEX) is an almost circular ribbon of a {approx}140{sup 0} opening angle, centered at (l, b) = (33{sup 0}, 55{sup 0}), covering the part of the celestial sphere with the lowest column densities of the Local Interstellar Cloud (LIC). We propose a novel interpretation of the IBEX results based on the idea of ENA produced by charge exchange between the neutral H atoms at the nearby edge of the LIC and the hot protons ofmore » the Local Bubble (LB). These ENAs can reach the Sun's vicinity because of very low column density of the intervening LIC material. We show that a plane-parallel or slightly curved interface layer of contact between the LIC H atoms (n {sub H} = 0.2 cm{sup -3}, T = 6000-7000 K) and the LB protons (n {sub p} = 0.005 cm{sup -3}, T {approx} 10{sup 6} K), together with an indirect contribution coming from multiply scattered ENAs from the LB, may be able to explain both the shape of the ribbon and the observed intensities, provided that the edge is <(500-2000) AU away, the LIC proton density is (correspondingly) < (0.04-0.01) cm{sup -3}, and the LB contains {approx}1% of non-thermal protons over the IBEX energy range. If this model is correct, then IBEX, for the first time, has imaged in ENAs a celestial object beyond the confines of the heliosphere and can directly diagnose the plasma conditions in the LB.« less
  • Following the high-precision determination of the velocity vector and temperature of the pristine interstellar neutral (ISN) He via a coordinated analysis summarized by McComas et al., we analyzed the Interstellar Boundary Explorer (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 (WB) persists. We used the same simulation model and a parameter fitting method very similar to that used for the analysis of ISN He. We approximated the parent population of the WB in front of themore » heliosphere with a homogeneous Maxwell–Boltzmann distribution function and found a temperature of ∼9500 K, an inflow speed of 11.3 km s{sup −1}, and an inflow longitude and latitude in the J2000 ecliptic coordinates 251.°6, 12.°0. The abundance of the WB relative to ISN He is 5.7% and the Mach number is 1.97. The newly determined inflow direction of the WB, the inflow directions of ISN H and ISN He, and the direction to the center of the 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 WB. This co-planarity lends support to the hypothesis that the WB is the secondary population of ISN He and that the center of the Ribbon coincides with the direction of the local interstellar magnetic field (ISMF). The common plane for the direction of the inflow of ISN gas, ISN H, the WB, and the local ISMF is given by the normal direction: ecliptic longitude 349.°7 ± 0.°6 and latitude 35.°7 ± 0.6 in the J2000 coordinates, with a correlation coefficient of 0.85.« less
  • We have developed a refined and optimized version of the Warsaw Test Particle Model of interstellar neutral gas in the heliosphere, specially tailored for analysis of IBEX-Lo observations. The former version of the model was used in the analysis of neutral He observed by IBEX that resulted in an unexpected conclusion that the interstellar neutral He flow vector was different than previously thought and that a new population of neutral He, dubbed the Warm Breeze, exists in the heliosphere. It was also used in the reanalysis of Ulysses observations that confirmed the original findings on the flow vector, but suggestedmore » a significantly higher temperature. The present version of the model has two strains targeted for different applications, based on an identical paradigm, but differing in the implementation and in the treatment of ionization losses. We present the model in detail and discuss numerous effects related to the measurement process that potentially modify the resulting flux of ISN He observed by IBEX, and identify those of them that should not be omitted in the simulations to avoid biasing the results. This paper is part of a coordinated series of papers presenting the current state of analysis of IBEX-Lo observations of ISN He. Details of the analysis method are presented by Swaczyna et al. and results of the analysis are presented by Bzowski et al.« less