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Insights Into the Beginnings of Cosmic Rays

NSF Award:

Analysis of IceCube Data at UW-Madison 2010-2013  (University of Wisconsin-Madison)

IceCube Maintenance and Operations 2010-2015  (University of Wisconsin-Madison)

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Analysis of data from the IceCube Neutrino Observatory, a massive detector deployed in Antarctica's deep ice, has provided insight into one of the most enduring mysteries in physics--the production of cosmic rays. These are electrically charged particles--such as protons--that strike the Earth from all directions with energies up to 100 million times higher than those created in man-made accelerators.

IceCube researchers found no neutrinos in a survey of 300 gamma ray bursts (GRBs) that occurred between May 2008 and April 2010 and detected by the SWIFT and Fermi satellites. This result contradicts 15 years of predictions and challenges the theory that GRBs produce the highest energy cosmic rays.

In light of these findings, astronomers are reevaluating the theory for the production of cosmic rays and neutrinos in a GRB fireball and possibly the theory that high-energy cosmic rays are generated in fireballs. The lack of neutrinos implies either that GRBs are not the only source of highly energetic cosmic rays or that the efficiency of neutrino production is much lower than has been predicted.

GRBs--the universe's most powerful explosions--are usually first observed by satellites using X-rays and/or gamma rays. GRBs are seen about once a day and are so bright they can be seen from half way across the visible universe. The explosions usually last only a few seconds and during this brief time they can outshine everything else in the universe.

These findings were published in Nature.

Image

  • a small group gathers for deployment of the final group of digital optical modules
The final string of digial optical modules deploys.
Peter Rejcek, NSF

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