Search for steady point-like sources in the astrophysical muon neutrino flux with 8 years of IceCube data

Abstract

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

$$\sim 1^\circ $$

∼

1 ∘

at 1 TeV and improves to

$$\sim 0.3^\circ $$

∼ 0 .

3 ∘

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

$$\sim 35\%$$

∼ 35 %

assuming an

$$E^{-2}$$

E

- 2

spectrum. The sensitivity on the muon-neutrino flux is at a level of

$$E^2 \mathrm {d} N /\mathrm {d} E = 3\cdot 10^{-13}\,\mathrm {TeV}\,\mathrm {cm}^{-2}\,\mathrm {s}^{-1}$$

E 2

d N / d E = 3 ·

10

- 13

TeV

cm

- 2

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.