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 =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 spectralmore » 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:

Desai, M. I. ^[1]; Allegrini, F. ^[1]; Dayeh, M. A. ^[2]; Funsten, H. ^[3]; Heerikhuisen, J. ^[4]; McComas, D. J. ^[1]; Fuselier, S. A. ^[1]; Pogorelov, N. ^[4]; Schwadron, N. A. ^[5]; Zank, G. P. ^[4]; Zirnstein, E. J. ^[6]

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+ Show Author Affiliations

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:

Mon Mar 30 00:00:00 EDT 2015

Research Org.:

Univ. of Alabama, Huntsville, AL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Fusion Energy Sciences (FES); National Science Foundation (NSF); National Aeronautics and Space Administration (NASA)

OSTI Identifier:

1326074

Grant/Contract Number:  

SC0008334; NNX11AB48G; NNX12AH44G; NNX12AB30G; NNX14AJ53G; OCI-1144120

Resource Type:

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