Can BL Lac emission explain the neutrinos above 0.2 PeV? [HEAP]

We investigate whether the highest energy neutrinos observed by IceCube are produced by BL Lacs, a reasonable hypothesis that does not contradict severely any known fact. We test it by searching for correlations between the through-going muon events of IceCube and the BL Lacs of the second catalogue of Fermi-LAT (2FHL). If the BL Lac are the main source of the neutrinos, we expect 10.2 +- 2.4 correlated events but we find that just 1 event has a BL Lac as counterpart. We conclude that the hypothesis that the BL Lacs are the main emitters of the observed astrophysical neutrinos can be excluded at 3.7 sigma. The significance increases to 4.1 sigma if we exclude the two through- going events whose directions is poorly reconstructed. We discuss how much the angular resolution uncertainties should be increased, in order to reconcile this hypothesis with observations, finding that this requires a very large value of 4 degrees. We assess the probability to observe one multiplet from the same source, assuming that BL Lacs are the true emitters of high energy neutrinos, finding that the present null result is not yet of critical significance. The methodological value of this type of multi-messenger approach is emphasized.

Read this paper on arXiv…

A. Palladino and F. Vissani
Wed, 1 Mar 17

Comments: 9 pages, 6 figures