University of Wisconsin-Madison

IceCube cosmic ray data contributes to understanding of interstellar space

In a paper recently published in Science Express, cosmic ray data from IceCube was used alongside observations from NASA's Interstellar Boundary Explorer, or IBEX, in a study of the magnetic fields that surround our solar system.

IBEX orbits the Earth looking at interstellar space beyond the heliosphere, a magnetized bubble of charged particles around the sun. The satellite detects energetic neutral atoms generated during interactions at the heliosphere border. Some energetic neutral atoms observed by IBEX are thought to have originated from the electron-stripped ions trapped by the interstellar magnetic field outside the heliosphere.

While IceCube is primarily designed to record high-energy neutrino interactions, the detector is constantly bombarded by cosmic ray muons. In 2010, the IceCube Collaboration published a study reporting evidence of an anisotropy in the arrival direction of cosmic rays. Subsequent studies have reinforced the influence of magnetic fields on cosmic ray particles.

Based on IBEX data on energetic neutral atoms, researchers developed a model of the magnetic system in interstellar space. Cosmic ray data from IceCube and the Tibet AS-gamma experiment confirmed their model.

On the left, a map of cosmic ray arrival data gathered by IceCube and Tibet AS-gamma.  On the right, an IBEX prediction of cosmic ray data.  Red signifies a concentration of cosmic rays, and blue a deficit. Credit: NASA/IBEX/UNH
On the left, a map of cosmic ray arrival data gathered by IceCube and Tibet AS-gamma. On the right, an IBEX prediction of cosmic ray data. Red signifies a concentration of cosmic rays, and blue a deficit. Credit: NASA/IBEX/UNH

“The magnetic field that drapes around the heliosphere has a similar influence on low-energy particles, like those that produce energetic neutral atoms in the KeV range, and high-energy particles like the TeV cosmic rays that IceCube sees,” says Paolo Desiati, an IceCube researcher at the Wisconsin IceCube Particle Astrophysics Center. High-energy cosmic rays are generated in unknown sources in the galaxy but interact with the magnetic system around the heliosphere in a similar way to particles created at its edge.

“It’s interesting to use IceCube data in a different way,” explains Desiati. “Traditionally, we are looking at astrophysical sources of neutrinos and cosmic rays. The interstellar medium is a much closer environment.”

  1. Info: “Global Anisotropies in TeV Cosmic Rays Related to the Sun’s Local Galactic Environment from IBEX,” N.A. Schwadron, et al. Science, 1245026 (2014). DOI: 10.1126/science.1245026