University of Wisconsin-Madison

Astrophysical muon neutrino flux in the northern sky with 2 years of IceCube data (released 20 Aug 2015)

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Astrophysical muon neutrino flux in the northern sky with 2 years of IceCube data (preview)

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Results from the IceCube Neutrino Observatory have recently provided compelling evidence for the existence of a high energy astrophysical neutrino flux utilizing a dominantly Southern Hemisphere data set consisting primarily of νe and ντ charged-current and neutral-current (cascade) neutrino interactions.

In the analysis presented here, a data sample of approximately 35000 muon neutrinos from the Northern sky is extracted from data taken during 659.5 days of live time recorded between May 2010 and May 2012.

While this sample is composed primarily of neutrinos produced by cosmic ray interactions in Earth's atmosphere, the highest energy events are inconsistent with a hypothesis of solely terrestrial origin at 3.7σ significance.

These neutrinos can, however, be explained by an astrophysical flux per neutrino flavor at a level of Φ(Eν) = 9.9+3.9
× 10-19 GeV-1 cm-2 sr-1 s-1 (Eν / 100TeV)-2, consistent with IceCube's Southern-Hemisphere-dominated result.

Additionally, a fit for an astrophysical flux with an arbitrary spectral index is performed.

We find a spectral index of 2.2+0.2
, which is also in good agreement with the Southern Hemisphere result.

Evidence for Astrophysical Muon Neutrinos from the Northern Sky with IceCube, IceCube Collaboration, Physical Review Letters 115 (2015) 081102.

See paper in PRL

Data release

Astrophysical muon neutrino flux in the northern sky with 2 years of IceCube data (.zip)

Included in the download are the following files:

  • HE_NuMu_data.txt - This file summarizes properties of the events found in this sample likely to have the highest energies. Only events with energy proxy values larger than 5e4 are included. The time at which each event was observed is given as a modified julian date, and the reconstructed astronomical coordinates of the each event's origin are given in the J2000 reference frame. The reconstructed directions for these events are expected to have a median angular resolution of about 0.4°. The values of the energy proxy which were used in the flux fit are included, as well as the estimates most probable muon and neutrino energies for these events assuming the best fit spectrum resulting from that fit. It should be noted that the precision of these estimates is expected to be fairly low, giving them uncertainties of a factor of 2 or larger in most cases. Finally, the probability that each event is drawn from the diffuse astrophysical flux is included, based on the assumption that this flux and the atmospheric backgrounds are described by the result of the flux fit. Download a pdf copy of this table here.
  • effective_area_release.tar - These files contain information intended to make it practical to compute expected event rates for theoretical fluxes which may be compared to the observations of this analysis. Please read the document README_effective_area.txt for further details.
  • HE_NuMu_skymap.pdf - Mollweide projection in equatorial coordinates of the arrival direction of events of this analysis with energy proxy MuEx > 50 (⊙). The most probable neutrino energy (in TeV) indicated for each event assumes the best-fit astrophysical flux of the analysis. For comparison, the events of the 3-year high-energy starting event (HESE) analysis with deposited energy larger than 60 TeV (tracks ⊗ & cascades ⊕) are also shown. Cascade events (⊕) are indicated together with their median angular uncertainty (thin circles). One event (*) appears in both event samples. The grey-shaded region indicate the zenith angle range where Earth absorption of 100 TeV neutrinos is larger than 90%.
  • HE_NuMu_eventviews.pdf - contains event displays for each of the 21 events.
  • observed_events - This file contains the complete list of events experimentally observed in this data sample. Unlike the highest energy events listed in HE_NuMu_data.txt only the minimal information used in this analysis is included: The IceCube event ID number, the data-taking period, labeled by year, in which the event was observed, the reconstructed energy proxy value, and the cosine of the reconstructed zenith angle.

Data release updated on May 18, 2016

For any questions about this data release, please write to