Galactic cosmic rays consist of protons, electrons and ions, most of which are believed to be accelerated to relativistic speeds in supernova remnants. All components of the cosmic rays show an intensity that decreases as a power law with increasing energy (for example as E(-2.7)). Electrons in particular lose energy rapidly through synchrotron and inverse Compton processes, resulting in a relatively short lifetime (about 10(5) years) and a rapidly falling intensity, which raises the possibility of seeing the contribution from individual nearby sources (less than one kiloparsec away). Here we report an excess of galactic cosmic-ray electrons at energies of approximately 300-800 GeV, which indicates a nearby source of energetic electrons. Such a source could be an unseen astrophysical object (such as a pulsar or micro-quasar) that accelerates electrons to those energies, or the electrons could arise from the annihilation of dark matter particles (such as a Kaluza-Klein particle with a mass of about 620 GeV).

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 ~200GeV/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 ~10 15 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.

We present new measurements of the energy spectra of cosmic-ray (CR) nuclei from the second flight of the balloon-borne experiment Cosmic Ray Energetics And Mass (CREAM). The instrument included different particle detectors to provide redundant charge identification and measure the energy of CRs up to several hundred TeV. The measured individual energy spectra of C, O, Ne, Mg, Si, and Fe are presented up to ∼ 10 14 eV. The spectral shape looks nearly the same for these primary elements and it can be fitted to an E −2.66±0.04 power law in energy. Moreover, a new measurement of the absolute intensity of nitrogen in the 100-800 GeV/n energy range with smaller errors than previous observations, clearly indicates a hardening of the spectrum at high energy. The relative abundance of N/O at the top of the atmosphere is measured to be 0.080 ± 0.025 (stat.) ±0.025 (sys.) at ∼ 800 GeV/n, in good agreement with a recent result from the first CREAM flight.

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We present new measurements of heavy cosmic-ray nuclei at high energies performed during the first flight of the balloon-borne cosmic-ray experiment CREAM (Cosmic-Ray Energetics And Mass). This instrument uses multiple charge detectors Preprint submitted to Elsevier 12 August 2008and a transition radiation detector to provide the first high accuracy measurements of the relative abundances of elements from boron to oxygen up to energies around 1 TeV/n. The data agree with previous measurements at lower energies and show a relatively steep decline (∼ E −0.6 to E −0.5 ) at high energies. They further show the source abundance of nitrogen relative to oxygen is ∼ 10% in the TeV/n region.

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The Cosmic Ray Energetics And Mass (CREAM) experiment is designed to investigate high energy (10 12 ~ 10 15 eV) cosmic rays over the elemental range from hydrogen to iron (1 ≤ Z ≤ 26), through a series of long balloon flights. Originally planned to be flown on the first of the new Ultra Long Duration Balloon (ULDB) being developed by NASA, the CREAM instrument was launched as a long duration balloons (LDB) payload from McMurdo Station, Antarctica on December 16, 2004 and flew for a record-breaking 42 days. A second CREAM flight one year later lasted 28 days. The CREAM design is unique in that it obtains two independent energy measurements using a tungsten/scintillator sampling calorimeter and a Transition Radiation Detector (TRD) with up to four independent charge measurements of incident particles using a novel Timing-based scintillator Charge Detector (TCD), a plastic Cherenkov Detector (CD), scintillating fiber hodoscopes, and a Silicon Charge Detector (SCD). The energy limits are determined by trigger efficiency and telemetry bandwidth at the low end and by statistics at the high end.

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