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Title: Latittudinal and energy dependence of energetic neutral atom spectral indices measured by the Interstellar Boundary Explorer

Abstract

Here, we investigate the latitudinal and energy dependence of the globally distributed 0.5-6 keV energetic neutral atom (ENA) spectra measured by the Interstellar Boundary Explorer (IBEX) during the first 3 yrs of the mission. Our results are: (1) the ENA spectral indices at the two lowest energies (0.89 and 1.47 keV) exhibit no clear trend with ecliptic latitude θ, while those at ~2.29 and ~3.41 keV exhibit a clear latitudinal pattern; flatter spectra occur above 60° latitude and steeper spectra occur ±30° of the equator. (2) The latitudinal dependence of the spectral indices at different energies can be represented by the cosine function γ =a 0 + a 1 cos (a 2θ) with unique offsets, amplitudes, and phase angles; the higher energy ENA indices transition to successively larger amplitudes within ±45° of the equator. The results confirm the previously reported latitudinal organization of the ENA spectra and their remarkable similarity to that of the solar wind (SW) speed observed by Ulysses in the inner heliosphere. And while earlier studies showed that the ~0.5-6 keV globally distributed ENA spectral indices could be represented as single power laws over much of the sky, our new results indicate that this is an over-simplificationmore » because the spectral indices have an energy and latitude dependence. Furthermore, this dependence is an important factor that must be taken into consideration by models and simulations that seek to map the IBEX ENA observations back to the latitudinal profile of the SW speed structure observed in the inner heliosphere.« less

Authors:
 [1];  [1];  [2];  [3];  [4];  [1];  [1];  [4];  [5];  [4];  [6]
  1. Southwest Research Inst. (SwRI), San Antonio, TX (United States); Univ. of Texas, San Antonio, TX (United States). Dept. of Physics and Astronomy
  2. Southwest Research Inst. (SwRI), San Antonio, TX (United States)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  4. Univ. of Alabama, Huntsville, AL (United States). Center for space Plasma and Aeronomic Research and Dept. of Space Science
  5. Univ. of New Hampshire, Durham, NH (United States). Dept. of Physics and Space Science Center; Southwest Research Inst. (SwRI), San Antonio, TX (United States)
  6. Univ. of Alabama, Huntsville, AL (United States). Center for space Plasma and Aeronomic Research
Publication Date:
Research Org.:
Univ. of Alabama, Huntsville, AL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); National Science Foundation (NSF); National Aeronautic and Space Administration (NASA)
OSTI Identifier:
1326074
Grant/Contract Number:  
SC0008334; NNX11AB48G; NNX12AH44G; NNX12AB30G; NNX14AJ53G; OCI-1144120
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 802; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; ISM: atoms; magnetohydrodynamics (MHD); shock waves; solar wind; Sun: heliosphere

Citation Formats

Desai, M. I., Allegrini, F., Dayeh, M. A., Funsten, H., Heerikhuisen, J., McComas, D. J., Fuselier, S. A., Pogorelov, N., Schwadron, N. A., Zank, G. P., and Zirnstein, E. J.. Latittudinal and energy dependence of energetic neutral atom spectral indices measured by the Interstellar Boundary Explorer. United States: N. p., 2015. Web. doi:10.1088/0004-637X/802/2/100.
Desai, M. I., Allegrini, F., Dayeh, M. A., Funsten, H., Heerikhuisen, J., McComas, D. J., Fuselier, S. A., Pogorelov, N., Schwadron, N. A., Zank, G. P., & Zirnstein, E. J.. Latittudinal and energy dependence of energetic neutral atom spectral indices measured by the Interstellar Boundary Explorer. United States. doi:10.1088/0004-637X/802/2/100.
Desai, M. I., Allegrini, F., Dayeh, M. A., Funsten, H., Heerikhuisen, J., McComas, D. J., Fuselier, S. A., Pogorelov, N., Schwadron, N. A., Zank, G. P., and Zirnstein, E. J.. Mon . "Latittudinal and energy dependence of energetic neutral atom spectral indices measured by the Interstellar Boundary Explorer". United States. doi:10.1088/0004-637X/802/2/100. https://www.osti.gov/servlets/purl/1326074.
@article{osti_1326074,
title = {Latittudinal and energy dependence of energetic neutral atom spectral indices measured by the Interstellar Boundary Explorer},
author = {Desai, M. I. and Allegrini, F. and Dayeh, M. A. and Funsten, H. and Heerikhuisen, J. and McComas, D. J. and Fuselier, S. A. and Pogorelov, N. and Schwadron, N. A. and Zank, G. P. and Zirnstein, E. J.},
abstractNote = {Here, we investigate the latitudinal and energy dependence of the globally distributed 0.5-6 keV energetic neutral atom (ENA) spectra measured by the Interstellar Boundary Explorer (IBEX) during the first 3 yrs of the mission. Our results are: (1) the ENA spectral indices at the two lowest energies (0.89 and 1.47 keV) exhibit no clear trend with ecliptic latitude θ, while those at ~2.29 and ~3.41 keV exhibit a clear latitudinal pattern; flatter spectra occur above 60° latitude and steeper spectra occur ±30° of the equator. (2) The latitudinal dependence of the spectral indices at different energies can be represented by the cosine function γ =a0 + a1 cos (a2θ) with unique offsets, amplitudes, and phase angles; the higher energy ENA indices transition to successively larger amplitudes within ±45° of the equator. The results confirm the previously reported latitudinal organization of the ENA spectra and their remarkable similarity to that of the solar wind (SW) speed observed by Ulysses in the inner heliosphere. And while earlier studies showed that the ~0.5-6 keV globally distributed ENA spectral indices could be represented as single power laws over much of the sky, our new results indicate that this is an over-simplification because the spectral indices have an energy and latitude dependence. Furthermore, this dependence is an important factor that must be taken into consideration by models and simulations that seek to map the IBEX ENA observations back to the latitudinal profile of the SW speed structure observed in the inner heliosphere.},
doi = {10.1088/0004-637X/802/2/100},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 802,
place = {United States},
year = {Mon Mar 30 00:00:00 EDT 2015},
month = {Mon Mar 30 00:00:00 EDT 2015}
}

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