The energy-dependent position of the IBEX ribbon

[CosmicLettuce]

The energy-dependent position of the IBEX ribbon due to the solar wind structure

http://arxiv.org/abs/1604.05079

Observations of energetic neutral atoms (ENAs) allow for remote studies of the plasma condition in the heliosphere and the neighboring local interstellar medium. The first IBEX results revealed an arc-like enhancement of the ENA flux in the sky, known as the ribbon. The ribbon was not expected from the heliospheric models prior to the IBEX launch. One of the proposed explanations of the ribbon is the mechanism of the secondary ENA emission. The ribbon reveals energy-dependent structure in the relative intensity along its circumference and in the position. Namely, the ribbon geometric center varies systematically by about 10∘ in the energy range 0.7-4.3 keV. Here, we show by analytic modeling that this effect is a consequence of the helio-latitudinal structure of the solar wind reflected in the secondary ENAs. Along with a recently measured distance to the ribbon source just beyond the heliopause, our findings support the connection of the ribbon with the local interstellar magnetic field by the mechanism of the secondary ENA emission. However, the magnitude of the center shift in the highest IBEX energy channel is much larger in the observations than expected from the modeling. This may be due to another, not currently recognized, process of ENA generation.

[Cargo]

Science can only progress if we cast aside such silly words like "wind" in space.

[The Great Dog]

Picture of the Day from 4.15.16: Reflections

One important thing to remember is that the ISM contains ionized particles. It is those electrons and positive ions that are critical to understanding the behavior of the ISM and how the Solar System interacts with it. If electric charge separation takes place in different regions of the ISM, a weak electric field will develop. An electric field, no matter how weak, initiates electric charge flow, or electric current. Since the ISM is not electrically neutral, it should be thought of as a plasma.

In the consensus view, solar wind protons acquire electrons in collisions with hydrogen atoms already located in the heliosheath. If it is teardrop shaped, ENAs would be distributed around the sky in a more-or-less uniform pattern. IBEX observations revealed a “ribbon” of increased ENAs perpendicular to the galactic magnetic field. The teardrop is a sphere.

Langmuir sheaths are electrically charged double layers of plasma, in which opposite charges build up near each other, creating an electric field between them. Double layers can accelerate ions to extreme velocities. Where the solar magnetosphere, or heliosphere, meets the dissimilar charge of the ISM, two regions of dissimilar plasma will form a Langmuir sheath between them, which leads to a spherical formation.