ABSTRACT
The association of two IceCube detections, the IceCube-170922A event and a neutrino flare, with the blazar TXS 0506+056, has paved the way for the multimessenger quest for cosmic ...accelerators. IceCube has observed many other neutrinos but their origin remains unknown. To better understand the reason for the apparent lack of neutrino counterparts, we have extended the comprehensive dissection of the sky area performed for the IceCube-170922A event to all 70 public IceCube high-energy neutrinos that are well reconstructed and off the Galactic plane. Using the multifrequency data available through the Open Universe platform, we have identified numerous candidate counterparts of IceCube events. We report here the classification of all the γ-ray blazars found and the results of subsequent statistical tests. In addition, we have checked the 4LAC, 3FHL, and 3HSP catalogues for potential counterparts. Following the dissection of all areas associated with IceCube neutrinos, we evaluate the data using a likelihood-ratio test and find a $3.23\, \sigma$ (post-trial) excess of HBLs and IBLs with a best fit of 15 ± 3.6 signal sources. This result, together with previous findings, consistently points to a growing evidence for a connection between IceCube neutrinos and blazars, the most energetic particle accelerators known in the Universe.
The uncertainty region of the highly energetic neutrino IceCube200107A includes 3HSP J095507.9+355101 (
z
= 0.557), an extreme blazar, which was detected in a high, very hard, and variable X-ray ...state shortly after the neutrino arrival. Following a detailed multiwavelength investigation, we confirm that the source is a genuine BL Lac. This new detection differs from TXS 0506+056, which is thus far the first source associated with IceCube neutrinos, and is considered a “masquerading” BL Lac. As in the case of TXS 0506+056, 3HSP J095507.9+355101 is also way off the so-called blazar sequence. We consider 3HSP J095507.9+355101 a possible counterpart to the IceCube neutrino. Finally, we discuss some theoretical implications in terms of neutrino production.
This Letter presents the results from pointlike neutrino source searches using ten years of IceCube data collected between April 6, 2008 and July 10, 2018. We evaluate the significance of an ...astrophysical signal from a pointlike source looking for an excess of clustered neutrino events with energies typically above ∼1 TeV among the background of atmospheric muons and neutrinos. We perform a full-sky scan, a search within a selected source catalog, a catalog population study, and three stacked Galactic catalog searches. The most significant point in the northern hemisphere from scanning the sky is coincident with the Seyfert II galaxy NGC 1068, which was included in the source catalog search. The excess at the coordinates of NGC 1068 is inconsistent with background expectations at the level of 2.9σ after accounting for statistical trials from the entire catalog. The combination of this result along with excesses observed at the coordinates of three other sources, including TXS 0506+056, suggests that, collectively, correlations with sources in the northern catalog are inconsistent with background at 3.3σ significance. The southern catalog is consistent with background. These results, all based on searches for a cumulative neutrino signal integrated over the 10 years of available data, motivate further study of these and similar sources, including time-dependent analyses, multimessenger correlations, and the possibility of stronger evidence with coming upgrades to the detector.
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 ≥ 3 σ significance level. Because of high neutrino energy resolution and low atmospheric neutrino backgrounds, this analysis provides the most detailed characterization of the neutrino flux at energies below ∼100 TeV 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 TeV remains a puzzle. In order to not violate the isotropic diffuse gamma-ray background as measured by the Fermi Large Area Telescope, it suggests the existence of astrophysical neutrino sources characterized by dense environments which are opaque to gamma rays.
Abstract
We present a measurement of the high-energy astrophysical muon–neutrino flux with the IceCube Neutrino Observatory. The measurement uses a high-purity selection of 650k neutrino-induced muon ...tracks from the northern celestial hemisphere, corresponding to 9.5 yr of experimental data. With respect to previous publications, the measurement is improved by the increased size of the event sample and the extended model testing beyond simple power-law hypotheses. An updated treatment of systematic uncertainties and atmospheric background fluxes has been implemented based on recent models. The best-fit single power-law parameterization for the astrophysical energy spectrum results in a normalization of
ϕ
@
100
TeV
ν
μ
+
ν
¯
μ
=
1.44
−
0.26
+
0.25
×
10
−
18
GeV
−
1
cm
−
2
s
−
1
sr
−
1
and a spectral index
γ
SPL
=
2.37
−
0.09
+
0.09
, constrained in the energy range from 15 TeV to 5 PeV. The model tests include a single power law with a spectral cutoff at high energies, a log-parabola model, several source-class-specific flux predictions from the literature, and a model-independent spectral unfolding. The data are consistent with a single power-law hypothesis, however, spectra with softening above one PeV are statistically more favorable at a two-sigma level.
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