Title: Variability in the Position of the IBEX Ribbon over Nine Years: More Observational Evidence for a Secondary ENA Source

Abstract

The ribbon of enhanced energetic neutral atom flux, discovered by the Interstellar Boundary Explorer (IBEX) in 2009, has redefined our understanding of the heliosphere's interaction with the local interstellar medium (LISM). Yet, its origin continues to be a topic of scientific debate. The ribbon is circular and traces the region where the putative LISM magnetic field (B_LISM) is perpendicular to the radial direction from the Sun. Using nine years of IBEX-Hi observations, we investigate the ribbon circularity and location as functions of time and energy. We provide updated locations of the ribbon center at five energy passbands (centered at 0.7, 1.1, 1.7, 2.7, and 4.3 keV) in ecliptic coordinates [longitude, latitude]: [217$$_˙^°$$dg41 ± 0$$_˙^°$$dg95, 44$$_˙^°$$dg36 ± 0$$_˙^°$$dg93], [219$$_˙^°$$dg72 ± 0$$_˙^°$$dg95, 41$$_˙^°$$dg50 ± 0$$_˙^°$$dg87], [220$$_˙^°$$dg51 ± 1$$_˙^°$$dg19, 39$$_˙^°$$dg96 ± 1$$_˙^°$$dg00], [218$$_˙^°$$dg08 ± 1$$_˙^°$$dg66, 38$$_˙^°$$dg44 ± 1$$_˙^°$$dg24], and [214$$_˙^°$$dg68 ± 1$$_˙^°$$dg48, 34$$_˙^°$$dg13 ± 1$$_˙^°$$dg19] respectively. The weighted mean center location over all energies and all years is [218$$_˙^°$$dg33 ± 0$$_˙^°$$dg68, 40$$_˙^°$$dg38 ± 0$$_˙^°$$dg88] and its radius is 74$$_˙^°$$dg81 ± 0$$_˙^°$$dg65. As viewed by IBEX at 1 au, we find that (1) the ribbon is stable over time, with distinct centers at each energy; (2) ribbon centers exhibit small temporal variations, likely caused by the solar wind (SW) speed and density variations; and (3) ribbon location in the sky appears to be driven by (i) the inherent alignment of the ribbon centers along the plane connecting the presumed B_LISM and the heliospheric upwind direction, and (ii) the variable SW structure along the heliographic meridian, further emphasizing that the ribbon source is outside the heliosphere.

Authors:

Dayeh, Maher A. ^[1]; Zirnstein, E. ^[2]; Desai, M. I. ^[1]; Funsten, Herbert O. III  ^[3];

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Fuselier, S. A. ^[1]; Heerikhuisen, J. ^[4]; McComas, David J. ^[2]; Schwadron, N. A. ^[5]; Szalay, J. R. ^[2]

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+ Show Author Affiliations

1. Southwest Research Inst., San Antonio, TX (United States)
2. Princeton Univ., NJ (United States)
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
4. Univ. of Alabama, Huntsville, AL (United States)
5. Univ. of New Hampshire, Durham, NH (United States)

Publication Date:

2019-07-09

Research Org.:

Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

National Aeronautic and Space Administration (NASA)

OSTI Identifier:

1597367

Report Number(s):

LA-UR-19-31222
Journal ID: ISSN 1538-4357

Grant/Contract Number:  

89233218CNA000001; 80NSSC17K0597; NNX17AB98G

Resource Type:

Accepted Manuscript

Journal Name:

The Astrophysical Journal (Online)

Additional Journal Information:

Journal Name: The Astrophysical Journal (Online); Journal Volume: 879; 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; ISM: kinematics and dynamics; ISM: magnetic fields; ISM: structure; solar wind; Sun: heliosphere