2020/01/31 by IceCube Collaboration, M. G. Aartsen, M. Ackermann +358 · 2 citations
Physics and Astronomy · #astro-ph.HE #astro-ph.CO
paper · pdf · doi:10.1103/physrevlett.125.121104
published as Phys. Rev. Lett. 125, 121104 (2020) · 4 figures, 4 tables, includes supplementary material
arxiv created 2020/08/10 · arxiv updated 2020/09/23
We report on the first measurement of the astrophysical neutrino flux using particle showers (cascades) in IceCube data from 2010 -- 2015. Assuming standard oscillations, the astrophysical neutrinos in this dedicated cascade sample are dominated (∼ 90 %) by electron and tau flavors. The flux, observed in the sensitive energy range from 16 TeV to 2.6 PeV, is consistent with a single power-law model as expected from Fermi-type acceleration of high energy particles at astrophysical sources. We find the flux spectral index to be γ=2.53±0.07 and a flux normalization for each neutrino flavor of ϕastro = 1.66+0.25-0.27 at E0 = 100 TeV, in agreement with IceCube's complementary muon neutrino results and with all-neutrino flavor fit results. In the measured energy range we reject spectral indices γ≤2.28 at ≥3σ significance level. Due to high neutrino energy resolution and low atmospheric neutrino backgrounds, this analysis provides the most detailed characterization of the neutrino flux at energies below ∼100 \rmTeV compared to previous IceCube results. Results from fits assuming more complex neutrino flux models suggest a flux softening at high energies and a flux hardening at low energies (p-value ≥ 0.06). The sizable and smooth flux measured below ∼ 100 \rmTeV remains a puzzle. In order to not violate the isotropic diffuse gamma-ray background as measured by the Fermi-LAT, it suggests the existence of astrophysical neutrino sources characterized by dense environments which are opaque to gamma-rays.