A possible generation mechanism for the IBEX ribbon from outside the heliosphere

Abstract

The brightest and most surprising feature in the first all-sky maps of Energetic Neutral Atoms (ENA) emissions (0.2-6 keV) produced by the Interstellar Boundary Explorer (IBEX) is an almost circular ribbon of a ~140° opening angle, centered at (l,b) = (33°, 55°), 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 of 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_H = 0.2 cm^-3, T = 6000-7000 K) and the LB protons (n_p = 0.005 cm^-3, T ~ 10^6 K), together with 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^-3, and the LB contains ~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 from beyond the confines of the heliosphere and can directly diagnose the plasma conditions in the LB.

Accepted by Ap.J.Lett.

References in corpus (5)

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• The Trouble with the Local Bubble
• Neutral H density at the termination shock: a consolidation of recent results
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• The Interstellar Magnetic Field Close to the Sun II
• The helium Warm Breeze in IBEX observations as a result of charge exchange collisions in the outer heliosheath
• Distance to the IBEX Ribbon Source Inferred from Parallax
• Ionization rates in the heliosheath and in astrosheaths
• Can IBEX Identify Variations in the Galactic Environment of the Sun using Energetic Neutral Atom (ENAs)?
• Helium Energetic Neutral Atoms from the Heliosphere: Perspectives for Future Observations
• On the Geometry of the IBEX Ribbon
• Assessment of energetic neutral He atom intensities expected from the IBEX Ribbon
• The Interstellar Boundary Explorer (IBEX): Tracing the Interaction between the Heliosphere and Surrounding Interstellar Material with Energetic Neutral Atoms
• Modeling Emission of Heavy Energetic Neutral Atoms from the Heliosphere