| Abstract: | The IceCube Neutrino Observatory has established the existence of a
high-energy all-sky neutrino flux of astrophysical origin. This discovery was
made using events interacting within a fiducial region of the detector
surrounded by an active veto and with reconstructed energy above 60 TeV,
commonly known as the high-energy starting event sample, or HESE. We revisit
the analysis of the HESE sample with an additional 4.5 years of data, newer
glacial ice models, and improved systematics treatment. This paper describes
the sample in detail, reports on the latest astrophysical neutrino flux
measurements, and presents a source search for astrophysical neutrinos. We give
the compatibility of these observations with specific isotropic flux models
proposed in the literature as well as generic power-law-like scenarios.
Assuming $
u_e:
u_mu:
u_ au=1:1:1$, and an equal flux of neutrinos and
antineutrinos, we find that the astrophysical neutrino spectrum is compatible
with an unbroken power law, with a preferred spectral index of
${2.87}^{+0.20}_{-0.19}$ for the $68.3\%$ confidence interval. |
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