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.

21 pages, 5 figures, published in ApJL (corresponding author: [email protected])

References in corpus (7)

• Observation of an anomalous positron abundance in the cosmic radiation
• Measurement of the Cosmic Ray e+ plus e- spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope
• Measurements of cosmic-ray secondary nuclei at high energies with the first flight of the CREAM balloon-borne experiment
• Composition of Primary Cosmic-Ray Nuclei at High Energies
• Evidence of a Curved Synchrotron Spectrum in the Supernova Remnant SN 1006
• A Cosmic Ray Resolution to the Superbubble Energy-Crisis
• OB Associations, Wolf-Rayet Stars, and the Origin of Galactic Cosmic Rays

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• p, He, and C to Fe cosmic-ray primary fluxes in diffusion models: Source and transport signatures on fluxes and ratios
• Discriminating the source of high-energy positrons with AMS-02
• "Discrepant hardenings" in cosmic ray spectra: a first estimate of the effects on secondary antiproton and diffuse gamma-ray yields
• Impact of the spectral hardening of TeV cosmic rays on the prediction of the secondary positron flux
• The XMM-Newton X-ray Spectra of the Most X-ray Luminous Radio-quiet ROSAT Bright Survey-QSOs: A Reference Sample for the Interpretation of High-redshift QSO Spectra