Synopsis: Anatomy of the Cosmic Ray Energy Spectrum

A new experiment finds structure in the cosmic ray spectrum at very high energies, supporting theories about the origin and propagation of cosmic rays.
Synopsis figure
Dinoj via Wikipedia Commons

High-energy cosmic rays reaching the Earth are only measured indirectly—through the cascade of particles, called air showers, that result from the collision of cosmic rays with atoms in the atmosphere. The spectrum of cosmic rays thus obtained contains a kink, or “knee,” where the spectrum, which falls steeply with energy, changes slope and begins to fall even more sharply. Past experiments have indicated that the knee results from a decrease in the flux of light nuclei. Astrophysical models indicate that this is the end of light-nuclei cosmic rays originating in our own Milky Way. The same models expect that heavier nuclei in the cosmic rays from our Galaxy will have a similar drop at a higher energy. Above this energy, the remaining cosmic rays should be of extragalactic origin.

Now, the air-shower experiment KASCADE-Grande is reporting in Physical Review Letters the observation of a second “knee.” The analysis separates “electron rich” showers (which should be the result of incoming light-nuclei cosmic rays) from “electron poor” showers (from heavy-nuclei cosmic rays), and finds that the second knee is enhanced in the spectrum from electron-poor events. This finding supports the interpretation that the second knee results from a decrease of the flux of heavy nuclei. Moreover, this structure occurs in the energy range expected for such heavy nuclei by astrophysical models. The result strongly supports these models of the origin of Galactic cosmic rays and gives important input for the study of extragalactic ultrahigh-energy cosmic rays. – Stanley Brown


Announcements

More Announcements »

Subject Areas

Astrophysics

Previous Synopsis

Particles and Fields

When Symmetries Conform to Theories

Read More »

Next Synopsis

Nanophysics

Meniscus Lithography

Read More »

Related Articles

Synopsis: Gravitational Waves May Hold Dark Matter Secret
Astrophysics

Synopsis: Gravitational Waves May Hold Dark Matter Secret

A theoretical analysis examines the possibility that the black holes detected by LIGO serve as dark matter. Read More »

Synopsis: Cosmic Magnetism Revisited
Cosmology

Synopsis: Cosmic Magnetism Revisited

An analysis of the polarized emission from some 3000 distant radio sources places a stringent upper limit on the strength of the cosmological magnetic field. Read More »

Viewpoint: Black Holes Produce Complexity Fastest
Astrophysics

Viewpoint: Black Holes Produce Complexity Fastest

Theoretical results suggest a precise speed limit on the growth of complexity in quantum gravity, set by fundamental laws and saturated by black holes. Read More »

More Articles