Letter

Nature 456, 362-365 (20 November 2008) | doi:10.1038/nature07477; Received 23 May 2008; Accepted 1 October 2008

An excess of cosmic ray electrons at energies of 300–800 GeV

J. Chang1,2, J. H. Adams3, H. S. Ahn4, G. L. Bashindzhagyan5, M. Christl3, O. Ganel4, T. G. Guzik6, J. Isbert6, K. C. Kim4, E. N. Kuznetsov5, M. I. Panasyuk5, A. D. Panov5, W. K. H. Schmidt2, E. S. Seo4, N. V. Sokolskaya5, J. W. Watts3, J. P. Wefel6, J. Wu4 & V. I. Zatsepin5

  1. Purple Mountain Observatory, CAS, 2 West Beijing Road, Nanjing 210008, China
  2. Max Planck Institute for Solar System Research, 2 Max Planck-Strasse, Katlenburg-Lindau 37191, Germany
  3. Marshall Space Flight Center, Huntsville, Alabama 35812, USA
  4. University of Maryland, Institute for Physical Science & Technology, College Park, Maryland 20742, USA
  5. Skobeltsyn Institute of Nuclear Physics, Moscow State University, Leninskie gory, GSP1, Moscow 119991, Russia
  6. Louisiana State University, Department of Physics and Astronomy, Baton Rouge, Louisiana 70803, USA

Correspondence to: J. P. Wefel6 Correspondence and requests for materials should be addressed to J.P.W. (Email: wefel@phunds.phys.lsu.edu).

Galactic cosmic rays consist of protons, electrons and ions, most of which are believed to be accelerated to relativistic speeds in supernova remnants1, 2, 3. 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 105 years) and a rapidly falling intensity, which raises the possibility of seeing the contribution from individual nearby sources (less than one kiloparsec away)4. Here we report an excess of galactic cosmic-ray electrons at energies of approx300–800 GeV, which indicates a nearby source of energetic electrons. Such a source could be an unseen astrophysical object (such as a pulsar5 or micro-quasar6) that accelerates electrons to those energies, or the electrons could arise from the annihilation of dark matter particles (such as a Kaluza–Klein particle7 with a mass of about 620 GeV).

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