A search for muon neutrinos coincident with Gamma-ray Bursts with the IceCube 59-String detector
Redl, Peter Christian
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Gamma-Ray Bursts (GRBs) are believed to be prime candidates to produce the cosmic ray flux above 10^18 eV. Cosmic rays are deflected by galactic and inter-galactic magnetic fields and do not point back to their source, therefore cosmic ray observations cannot confirm or rule out GRBs as a source. Leading theories predict that if GRBs are indeed responsible for the highest energy cosmic rays, then they would produce a detectable TeV-scale neutrino flux in a km^3 sized neutrino detector. Neutrinos are not deflected by magnetic fields and point back to their source, making it possible to correlate a neutrino flux with its source. The detection of a neutrino flux from GRBs would be strong evidence that GRBs are a source of the highest energy cosmic rays. IceCube is the first km^3 sized neutrino detector in the world and is therefore sensitive to the predicted TeV neutrino flux from GRBs. The finished detector consists of 5160 light-sensitive Digital Optical Modules (DOM) arranged on 86 Strings. There are 60 DOMs on a single string deployed at depths between 1450 and 2450 meters below the surface. The first IceCube String was deployed during the South Pole summer of 2004-2005 with construction of the IceCube detector finishing during the austral summer of 2011. The results presented here are from the 59-string detector, which operated from May 2009 to May 2010. IceCube is able to detect charged particles moving through its instrumented volume near the speed of light by detecting the Cherenkov light given off by those charged particles. Muon and anti-muon neutrinos produce secondary muons if they interact with a nucleon. If this interaction happens in or near the instrumented volume IceCube can detect those secondary muons. By searching for a neutrino signal coincident in time and space with satellite detected gamma rays from GRBs, the analysis presented here pushes the sensitivity for neutrinos from GRBs to 0.46 times the theoretically predicted neutrino flux. The result is combined with the previous search and a combined 90% upper limit of 0.22 times the theoretical predicted flux is set. The implication of this stringent limit on the model is discussed and future IceCube sensitivities are outlined. IceCube is the largest neutrino detector in the world and with this result has entered the era of neutrino astrophysics by constraining long standing astrophysical neutrino production models.