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Abstract
The IceCube Neutrino Observatory is the first 1 km3 neutrino telescope. Data were collected using the partially-completed IceCube detector in the 40-string configuration recorded between 2008 April 5 and 2009 May 20, totaling 375.5 days livetime. An unbinned maximum likelihood ratio method is used to search for astrophysical signals. The data sample contains 36,900 events: 14,121 front the northern sky, mostly muons induced by atmospheric neutrinos and 22,779 from the southern sky, mostly high energy atmospheric muons. The analysis includes time-integrated searches for individual point sources and targeted searches for specific stacked source classes and spatially extended sources. While this analysis is sensitive to TeV-PeV energy neutrinos in the northern sky, it is primarily sensitive to neutrinos with energy greater than about 1 PeV in the southern sky. A number of searches are performed and significances (given as p-values, the chance probability to occur with only background present) calculated: (1) a scan of the entire sky for point sources (p=18%), (2) a predefined list of 39 interesting source candidates (p=62%), (3) stacking 16 sources of TeV gamma rays observed by Milagro and Fermi, along with an unconfirmed hot spot (p=32%), (4) stacking 127 starburst galaxies ( p=100%), and (5) stacking five nearby galaxy clusters (p =78%). No evidence for a signal is found in any of the searches. Limits are set for neutrino fluxes from astrophysical sources over the entire sky and compared to predictions. The sensitivity is at least a factor of two better than previous searches (depending on declination), with 90% confidence level muon neutrino flux upper limits being between E 2dN/dE ∼ 2–200 × 10−12 TeV cm−2s−1 in the northern sky and between 3–700 × 10−12 TeV cm−2s−1 in the southern sky. The stacked source searches provide the best limits to specific source classes. For the case of supernova remnants, we are just a factor of three from ruling out realistic predictions. The full IceCube detector is expected to improve the sensitivity to E−2 sources by another factor of two in the first year of operation.
