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

• Published in: Nature 2008-11, Vol.456 (7220), p.362-365
• Main Authors: Chang, J., Adams, J. H., Ahn, H. S., Bashindzhagyan, G. L., Christl, M., Ganel, O., Guzik, T. G., Isbert, J., Kim, K. C., Kuznetsov, E. N., Panasyuk, M. I., Panov, A. D., Schmidt, W. K. H., Seo, E. S., Sokolskaya, N. V., Watts, J. W., Wefel, J. P., Wu, J., Zatsepin, V. I.
• Format: Article
• Language: English
• Subjects: Astronomy; Atomic properties; Atoms & subatomic particles; Cosmic background radiation; Cosmic rays; Dark matter; Data analysis; Discovery and exploration; Electrons; Evaluation; Humanities and Social Sciences; letter; multidisciplinary; Properties; Radio sources (Astronomy); Science; Science (multidisciplinary)
• ISSN: 0028-0836; 1476-4687; 1476-4679
• DOI: 10.1038/nature07477

High-energy cosmic rays The ATIC (Advanced Thin Ionizaton Calorimeter) cosmic-ray astronomy experiment sends helium balloons to altitudes of 35 km and more above Antarctica for up to 15 days at a time. These forays to the edge of space have resulted in the detection of an excess of Galactic cosmic-ray electrons at energies of around 300–800 GeV, which indicates a nearby source of energetic electrons. The source could be an unseen astrophysical object that accelerates electrons to those energies, or the electrons could arise from the annihilation of 'Kaluza-Klein' dark matter, an exotic concept predicted by theories of the Universe involving compactified extra dimensions. This paper reports an excess of galactic cosmic-ray electrons at energies of ∼300-800 GeV, which indicates a nearby source of energetic electrons. Such a source could be an unseen astrophysical object that accelerates electrons to those energies, or the electrons could arise from the annihilation of dark matter. Galactic cosmic rays consist of protons, electrons and ions, most of which are believed to be accelerated to relativistic speeds in supernova remnants 1 , 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 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) 4 . Here we report an excess of galactic cosmic-ray electrons at energies of ∼300–800 GeV, which indicates a nearby source of energetic electrons. Such a source could be an unseen astrophysical object (such as a pulsar 5 or micro-quasar 6 ) that accelerates electrons to those energies, or the electrons could arise from the annihilation of dark matter particles (such as a Kaluza–Klein particle 7 with a mass of about 620 GeV).