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Saturday, April 21, 2012

A Blue Flash in Ice

Little is known about the ultra high-energy cosmic rays that regularly penetrate the atmosphere. Recent IceCube research rules out the leading theory that they come from gamma ray bursts. (Credit: NSF/J. Yang)

Future directions 

The lack of observation of neutrinos in coincidence with GRBs implies, at face value, that the theoretical models need to be revisited. “Calculations embracing the concept that cosmic ray protons are the decay products of neutrons that escaped the magnetic confinement of the GRB fireball are supported by the research community and have been convincingly excluded by the present data,” says Francis Halzen, IceCube principle investigator and a professor of physics at the University of Wisconsin-Madison. "IceCube will continue to collect more data with a final, better calibrated and better understood detector in the coming years." Since April 2011, IceCube has collected neutrino data using the full detector array. With the larger detector, researchers can see more neutrinos, providing a “higher resolution” picture of the neutrino sky. See: Cosmic Rays: 100 years of mystery

See Also: IceCube Neutrino Observatory Explores Origin of Cosmic Rays




IceCube’s 5,160 digital optical modules are suspended from 86 strings reaching a mile and a half below the surface at the South Pole. Each sphere contains a photomultiplier tube and electronics to capture the faint flashes of muons speeding through the ice, their direction and energy – and thus that of the neutrinos that created them – tracked by multiple detections. At lower left is the processed signal of an energetic muon moving upward through the array, created by a neutrino that traveled all the way through the Earth.


“This result represents a coming-of-age of neutrino astronomy,” says Nathan Whitehorn from the University of Wisconsin-Madison, who led the recent GRB research with Peter Redl of the University of Maryland. “IceCube, while still under construction, was able to rule out 15 years of predictions and has begun to challenge one of only two major possibilities for the origin of the highest-energy cosmic rays, namely gamma-ray bursts and active galactic nuclei.”


Redl says, “While not finding a neutrino signal originating from GRBs was disappointing, this is the first neutrino astronomy result that is able to strongly constrain extra-galactic astrophysics models, and therefore marks the beginning of an exciting new era of neutrino astronomy.” The IceCube Collaboration’s report on the search appears in the April 19, 2012, issue of the journal Nature. See: Where Do the Highest-Energy Cosmic Rays Come From? Probably Not from Gamma-Ray Bursts

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