Sources and Formation of the Ribbon Observed by IBEX: ``... Good Things may be Close by''

Details Sources and Formation of the Ribbon Observed by IBEX: ``... Good Things may be Close by'' Sources and Formation of the Ribbon Observed by IBEX: ``... Good Things may be Close by''

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsh24a..08k&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SH24A-08

Physics

[2124] Interplanetary Physics / Heliopause And Solar Wind Termination, [2126] Interplanetary Physics / Heliosphere/Interstellar Medium Interactions, [2134] Interplanetary Physics / Interplanetary Magnetic Fields, [2151] Interplanetary Physics / Neutral Particles

Scientific paper

Taking the first images of heliospheric boundary with Energetic Neutral Atoms (ENAs), the Interstellar Boundary EXplorer (IBEX) discovered a giant structure across the sky, called “the Ribbon”. The location and the orientation of the Ribbon seem to be associated with the interstellar magnetic field. Fine structures as well as temporal variations^{1} have been found in the Ribbon. While there are first model attempts to explain its location in the sky and its possible formation, the source of this Ribbon is not yet known. It could well consist of several components, for instance, a static component whose source is deeper in the heliosheath or beyond and a dynamic component that is close to or at the termination shock. IBEX data show that the peak energy is around 1 keV, which strongly indicates a close association with the solar wind, either the bulk ions or the entrained pickup ions. Models have been proposed using a distant source region well beyond the heliopause (HP) that extend over several hundred AU into the interstellar medium, in which pickup ions from neutral solar wind produce ENAs by charge exchange. Such a model could produce a ribbon structure, however, temporal variations are difficult to explain. In this alternative model, we concentrate on a population of reflected solar wind ions reflected and gyrating at the termination shock (TS). A large fraction of the incident ions forms a gyrotropic distribution concentrated perpendicular to the upstream magnetic field direction. These ions will charge exchange with interstellar neutral atoms and thus may form a major source for the observed ENA flux, which forms the Ribbon. One advantage of such a model is that it allows relatively rapid time variations of the observed ENA flux. In this model, it is the global shape of the TS, mediated by the interstellar magnetic field, which controls the location of the enhanced ENA intensity as well as the width of the ribbon. The model assumption is that the external magnetic and/or gas dynamic pressure in the outer heliosheath shifts the HP and the TS closer to the Sun. This may result in a narrow ridge of pressure on the inner side of the heliopause. Hence, this would also provide a possibility to remotely sense the global structure of the TS with the Ribbon. We will discuss advantages, limitations, and new possibilities of such a model for the ribbon formation. ^{1} McComas et al, JGR, 2010, in press

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