Radio pulses from cosmic rays

Ultrahigh-energy cosmic rays (UHECRs), with energies exceeding 10^19eV, are rare. A random square kilometer on Earth is hit by a few dozen per century. But their trajectories, relatively undeflected by intergalactic magnetic fields, might reveal their enigmatic sources. So astrophysicists build enormous ground-detector arrays. But even the flagship 3000-km^2 Pierre Auger Observatory in Argentina, which has been recording UHECRs since 2004, has not yet harvested enough to yield robust evidence of anisotropy that might reveal a class of sources (see PHYSICS TODAY, May 2010, page 15). Now a serendipitous discovery by the ANITA collaboration …

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