Discrepant hardening observed in cosmic-ray elemental spectra
Abstract
The balloon-borne Cosmic Ray Energetics And Mass (CREAM) experiment launched five times from Antarctica has achieved a cumulative flight duration of about 156 days above 99.5% of the atmosphere. The instrument is configured with complementary and redundant particle detectors designed to extend direct measurements of cosmic-ray composition to the highest energies practical with balloon flights. All elements from protons to iron nuclei are separated with excellent charge resolution. Here we report results from the first two flights of ~70 days, which indicate hardening of the elemental spectra above ~200 GeV/nucleon and a spectral difference between the two most abundant species, protons and helium nuclei. These results challenge the view that cosmic-ray spectra are simple power laws below the so-called knee at ~1015 eV. This discrepant hardening may result from a relatively nearby source, or it could represent spectral concavity caused by interactions of cosmic rays with the accelerating shock. Other possible explanations should also be investigated.
Keywords
Cite
@article{arxiv.1004.1123,
title = {Discrepant hardening observed in cosmic-ray elemental spectra},
author = {H. S. Ahn and P. Allison and M. G. Bagliesi and J. J. Beatty and G. Bigongiari and J. T. Childers and N. B. Conklin and S. Coutu and M. A. DuVernois and O. Ganel and J. H. Han and J. A. Jeon and K. C. Kim and M. H. Lee and L. Lutz and P. Maestro and A. Malinin and P. S. Marrocchesi and S. Minnick and S. I. Mognet and J. Nam and S. Nam and S. L. Nutter and I. H. Park and N. H. Park and E. S. Seo and R. Sina and J. Wu and J. Yang and Y. S. Yoon and R. Zei and S. Y. Zinn},
journal= {arXiv preprint arXiv:1004.1123},
year = {2010}
}
Comments
21 pages, 5 figures, published in ApJL (corresponding author: [email protected])