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March 17, 2017

20170317_112038Christian Spiering (right) discussed some aspects of the searches with the IceCube detector, concentrating in particular on astrophysical neutrino studies. He showed two very energetic events (>500 TeV), which were nicknamed Ernie and Bert. They are above 1 PeV. Following that, there was an analysis for a high-energy neutrino flux. On the fourth year of data taking they took another high-energy event, “Big bird”, of 2 PeV.

For through-going muons, from six years of data (2009-2015) the muon energy spectra were shown to match the expectation from atmospheric source, with however some outliers. One was shown to have a deposited energy of 2.6+-0.3 PeV, with the most probable energy of 7 PeV. That is the highest-energy event in their sample.

The spectrum for astrophysical sources shows a power index of -2.13+-0.13. There is some tension between cascade and track analysis for the shape of the spectrum.

The flavor composition was studied. For a far-away astrophysical source, the normal assumption is that you get muons from pion decay. So you would have one electron neutrino per every two muon neutrinos at the source. If however the muon decay of pions were suppressed you would have a 0:1:0 ratio, while for neutron decay the ratio would be 1:0:0 at the source for the three flavours. The result is now an exclusion of the dominance of neutron decay sources.

A limit on cosmogenic and AGN neutrino fluxes has been extracted by looking at the extremely high energy tail of the spectrum, based on observing two events.


IceCube studied the Crab Nebula, which emits gamma rays. Assuming these come from pizeros, one can compute the flux of neutrinos from charged pions. This was constrained by the data. Constrains were also put on the flux from Blazars, and there is hope that one could detect neutrinos from these sources.

Neutrinos could also be observed in association with Gamma-Ray Bursts. They looked for coincidences with GRBs in their field of view among 506, and found one single low-significance coincidence, consistent with atmospheric background.







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