Abstract
The IceCube Collaboration has observed a high-energy astrophysical neutrino flux and recently found evidence for neutrino emission from the blazar TXS 0506+056. These results open a new window into the high-energy universe. However, the source or sources of most of the observed flux of astrophysical neutrinos remains uncertain. Here, a search for steady point-like neutrino sources is performed using an unbinned likelihood analysis. The method searches for a spatial accumulation of muon-neutrino events using the very high-statistics sample of about 497,000 neutrinos recorded by IceCube between 2009 and 2017. The median angular resolution is sim 1^circ at 1 TeV and improves to sim 0.3^circ for neutrinos with an energy of 1 PeV. Compared to previous analyses, this search is optimized for point-like neutrino emission with the same flux-characteristics as the observed astrophysical muon-neutrino flux and introduces an improved event-reconstruction and parametrization of the background. The result is an improvement in sensitivity to the muon-neutrino flux compared to the previous analysis of sim 35% assuming an E^{-2} spectrum. The sensitivity on the muon-neutrino flux is at a level of E^2 mathrm {d} N /mathrm {d} E = 3cdot 10^{-13},mathrm {TeV},mathrm {cm}^{-2},mathrm {s}^{-1}. No new evidence for neutrino sources is found in a full sky scan and in an a priori candidate source list that is motivated by gamma-ray observations. Furthermore, no significant excesses above background are found from populations of sub-threshold sources. The implications of the non-observation for potential source classes are discussed.
Highlights
Astrophysical neutrinos are thought to be produced by hadronic interactions of cosmic-rays with matter or radiation fields in the vicinity of their acceleration sites [1]
Since gamma-rays can arise from the interaction of relativistic leptons with lowenergy photons, only neutrinos are directly linked to hadronic interactions
No significant clustering was found in any of the hypotheses tests beyond the expectation from background. Both the full-sky scan of the Northern hemisphere and the p-values from the source list are compatible with pure background
Summary
Astrophysical neutrinos are thought to be produced by hadronic interactions of cosmic-rays with matter or radiation fields in the vicinity of their acceleration sites [1]. In 2013, the IceCube Collaboration reported the observation of an unresolved, astrophysical, high-energy, allflavor neutrino flux, consistent with isotropy, using a sample of events which begin inside the detector (‘starting events’) [3,4]. The stacking of the directions of known blazars has revealed no significant excess of astrophysical neutrinos at the locations of known blazars This indicates that blazars from the 2nd Fermi-LAT AGN catalogue contribute less than about 30% to the total observed neutrino flux assuming an unbroken powerlaw spectrum with spectral index of −2.5 [10].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
