Constraining the Low-Energy Cosmic Ray Spectrum

Details Constraining the Low-Energy Cosmic Ray Spectrum Constraining the Low-Energy Cosmic Ray Spectrum

May 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...212.0504i&link_type=abstract

American Astronomical Society, AAS Meeting #212, #5.04; Bulletin of the American Astronomical Society, Vol. 40, p.194

Astronomy and Astrophysics

Astronomy

Scientific paper

While the cosmic ray spectrum is easily observed at high energies, below about 100 MeV cosmic rays are excluded from the inner solar system by the magnetic field coupled to the solar wind. This means that the cosmic ray spectrum below 100 MeV cannot be directly observed. However, there are several secondary observables which can tell us about low-energy cosmic rays, including certain interstellar molecules, the abundances of light element isotopes such as 6Li, 7Li, 9Be, 10B, and 11B, and gamma rays. These observables arise as the result of cosmic ray ionization, spallation, and the excitation of nuclear states, respectively. We are attempting to devise a low-energy spectrum that is both physically motivated and able to reproduce the above observables.
Recent results from H3+ have shown that the average cosmic-ray ionization rate in diffuse interstellar clouds is about 2×10-16 s-1, an order of magnitude larger than previously thought. Using a proton spectrum that is composed of a propagated source spectrum and a low-energy component with high flux, we are able to reproduce the above result. This spectrum, combined with its alpha particle analog, generates light element abundances that are in rough accord with meteoritic values. For gamma rays, we predict a diffuse Galactic flux that is slightly below observable limits using current telescopes. We estimate that the energy budget in low-energy cosmic rays (those primarily responsible for ionization) is comparable to that in the observed (> 1 GeV) cosmic rays and thus represents a significant fraction of the mechanical power in Galactic supernovae.

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