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Science 20 October 2006:
Vol. 314. no. 5798, p. 381
DOI: 10.1126/science.314.5798.381c
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This Week in Science

One way in which the particles that become cosmic rays can obtain their high energy is through acceleration by shock waves, such as those produced by supernovas, including nearby ones within our own Galaxy. However, the paths that cosmic rays take are then scrambled by interstellar magnetic fields, which obscures their origin. Amenomori et al. (p. 439; see the Perspective by Duldig) have mapped the distribution of cosmic rays on the sky using 16 years of data from the Tibet Air Shower Array. They see clear anisotropies, including a component associated with the Cygnus spiral arm of the Milky Way. Although present at energies up to tens of teraelectron volts (TeV), the anisotropic spots disappear at an energy near 300 TeV. This result suggests that the spots arise through the galactic rather than heliospheric magnetic field, and corotate with the gas and stars in the Milky Way.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)