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| The IceCube diffuse cosmic neutrino spectrum. The best fit to the spectrum of neutrinos observed through the Earth is compared to the unfolded spectrum of events starting inside the detector. Also shown is the flux corresponding to a single candidate event (red) attributed to the Glashow resonance. Figure from Lu (2018).
Source publication
After updating the status of the measurements of the cosmic neutrino flux by the IceCube experiment, we summarize the evidence for the first identified source of cosmic rays and speculate on the connection between the two observations.
Contexts in source publication
Context 1
... addition to the double cascade candidates, we should also mention that a first candidate event has been attributed to the Glashow resonance. This event was identified in a search for partially contained events, and represents ∼ 6 PeV in energy deposited in the detector; See Figure 2 (Aartsen et al., 2017b;Lu, 2018). ...
Context 2
... by the multimessenger campaign, IceCube searched its archival neutrino data up to and including October 2017 in the direction of IC-170922A using the likelihood routinely used in previous searches. This revealed a spectacular burst of over a dozen high-energy neutrinos in 110 days in the 2014-2015 data with a spectral index similar to the one observed for the diffuse cosmic neutrino spectrum (Aartsen et al., 2018b). ...
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Citations
... Additionally, gamma rays can result from hadronic cascades via pion decay (Cao et al. 2024). Multimessenger studies further enhance our understanding, with gamma rays providing an essential channel for probing the astrophysical origins of high-energy particles, as demonstrated in magnetar and other sources (Sasse & Anjos 2022;Mocellin & Anjos 2022;Kumar et al. 2024;Heyl et al. 2010;Halzen & Kheirandish 2019). ...
Recent multi-wavelength observations have highlighted magnetars as significant sources of cosmic rays, particularly through their gamma-ray emissions. This study examines three magnetar regions -CXOU J171405.7-31031, Swift J1834-0846, and SGR 1806-20-known for emitting detectable electromagnetic signals. We assess the detectability of these regions using the upcoming Cherenkov Telescope Array Observatory (CTAO) by conducting an ON/OFF spectral analysis and compare the expected results with existing observations. Our findings indicate that CTAO will detect gamma-ray emissions from these three magnetar regions with significantly reduced emission flux errors compared to current instruments. In special, the study shows that the CXOUJ1714-3810 and SwiftJ1834-0846 magnetar regions can be observed by the full southern and northern CTAO arrays in just five hours of observation, with mean significances above 10 σ and 30 σ, respectively. This paper discusses the regions analyzed, presents key results, and concludes with insights drawn from the study.
... What is the optimal neutrino telescope design is, to a great extent, a matter of scientific taste. The typical benchmark is the sensitivity to neutrino point sources, whose discovery is the primary goal of neutrino telescopes since it allows detailed comparison with source models often using multi-messenger data [23][24][25][26] and opens opportunities to study very long baseline neutrino oscillations [27][28][29][30][31] flavors is one of the most important goals of neutrino astrophysics particle physics, since it explores neutrino oscillations in unprecedented scales [32]. This has, in fact, been demonstrated by the current Ice-Cube array, which has performed some of the most sensitive tests of Lorentz symmetry [33]. ...
Water-(Ice-) Cherenkov neutrino telescopes have played a pivotal role in the search and discovery of high-energy astrophysical neutrinos. Experimental collaborations are developing and constructing next-generation neutrino telescopes with improved optical modules (OMs) and larger geometrical volumes to increase their efficiency in the multi-TeV energy range and extend their reach to EeV energies. Although most existing telescopes share similar OM layouts, more layout options should be explored for next-generation detectors to maximize discovery capability. In this work, we study a set of layouts at different geometrical volumes and evaluate the signal event selection efficiency and reconstruction fidelity under both an only trigger-level linear regression algorithm and an offline Graph Neural Network (GNN) reconstruction. Our methodology and findings serve as first steps toward an optimized, global network of neutrino telescopes.
... It is also more than an order of magnitude larger than the upper limits placed by MAGIC and HAWC (Acciari et al. 2019;Willox et al. 2022) on ∼ TeV γ-ray emissions. High-energy neutrinos and γ-rays are simultaneously produced whenever CRs interact with ambient matter or radiation within or near cosmic accelerators (Halzen & Kheirandish 2019). The observed difference between neutrinos and γ-rays from NGC 1068 can not be explained by absorption by the extragalactic background light (EBL) (Murase 2022). ...
The recent IceCube detection of TeV neutrino emission from the nearby active galaxy NGC 1068 suggests that active galactic nuclei (AGN) could make a sizable contribution to the diffuse flux of astrophysical neutrinos. The absence of TeV -rays from NGC 1068 indicates neutrino production in the vicinity of the supermassive black hole, where the high radiation density leads to -ray attenuation. Therefore, any potential neutrino emission from similar sources is not expected to correlate with high-energy -rays. Disk-corona models predict neutrino emission from Seyfert galaxies to correlate with keV X-rays, as they are tracers of coronal activity. Using through-going track events from the Northern Sky recorded by IceCube between 2011 and 2021, we report results from a search for individual and aggregated neutrino signals from 27 additional Seyfert galaxies that are contained in the BAT AGN Spectroscopic Survey (BASS). Besides the generic single power-law, we evaluate the spectra predicted by the disk-corona model. Assuming all sources to be intrinsically similar to NGC 1068, our findings constrain the collective neutrino emission from X-ray bright Seyfert galaxies in the Northern Hemisphere, but, at the same time, show excesses of neutrinos that could be associated with the objects NGC 4151 and CGCG 420-015. These excesses result in a 2.7 significance with respect to background expectations.
... Possible venues may come from UHECRs above the Greisen-Zatsepin-Kuz'min (GZK) knee around ∼10 20 EeV (Greisen 1966; Zatsepin & Kuz'min 1966), with pions arising from the Δ resonance: p + γ CMB → Δ + → π 0 + p or more speculatively from proton decay (Sakharov 1967) p → e + + π 0 , p → μ + + π 0 (Tanabashi et al. 2018). Subsequently, π 0 → 2γ, and on average, the pionic photons would carry ∼1/2 of the parent pion's energy (Mészáros 2014;Halzen & Kheirandish 2019;Globus & Blandford 2023). GZK horizon of 100 Mpc would then apply to the sources in the latter case (Stecker 1968;Ding et al. 2021) whose precise value depends on the CR composition (Ahlers & Salvado 2011). ...
We measured the dipole of the diffuse γ -ray background (DGB), identifying a highly significant time-independent signal coincidental with that of the Pierre Auger UHECR. The DGB dipole is determined from flux maps in narrow energy bands constructed from 13 yr of observations by the Large Area Telescope (LAT) of the Fermi satellite. The γ -ray maps were clipped iteratively of sources and foregrounds similar to that done for the cosmic infrared background. The clipped narrow energy band maps were then assembled into one broad energy map out to the given energy starting at E = 2.74 GeV, where the LAT beam falls below the sky’s pixel resolution. Next we consider cuts in Galactic latitude and longitude to probe residual foreground contaminations from the Galactic plane and center. In the broad energy range 2.74 < E ≤ 115.5 GeV, the measured dipoles are stable with respect to the various Galactic cuts, consistent with an extragalactic origin. The γ -ray sky’s dipole/monopole ratio is much greater than that expected from the DGB clustering component and the Compton–Getting effect origin with reasonable velocities. At ≃(6.5–7)% it is similar to the Pierre Auger UHECRs with E UHECR ≥ 8 EeV, pointing to a common origin of the two dipoles. However, the DGB flux associated with the found DGB dipole reaches parity with that of the UHECR around E UHECR ≤ 1 EeV, perhaps arguing for a non-cascading mechanism if the DGB dipole were to come from the higher-energy UHECRs. The signal-to-noise ratio of the DGB dipole is largest in the 5–30 GeV range, possibly suggesting the γ -photons at these energies are the ones related to cosmic rays.
... The angular distribution of the expected extraterrestrial neutrino induced rate is dependent on the angular distribution of the flux incident on Earth and the Earth's opacity to high-energy neutrinos. The flux incident on the Earth depends on the assumed astrophysical neutrino origin [112]. In this work, we consider two types of incident astrophysical neutrino fluxes: one that is assumed isotropic, and another that is anisotropic and originates from dark matter clustered around the galactic center. ...
In this work, we present the results of searches for signatures of dark matter decay or annihilation into Standard Model particles, and secret neutrino interactions with dark matter. Neutrinos could be produced in the decay or annihilation of galactic or extragalactic dark matter. Additionally, if an interaction between dark matter and neutrinos exists then dark matter will interact with extragalactic neutrinos. In particular galactic dark matter will induce an anisotropy in the neutrino sky if this interaction is present. We use seven and a half years of the High-Energy Starting Event (HESE) sample data, which measures neutrinos in the energy range of approximately 60 TeV to 10 PeV, to study these phenomena. This all-sky event selection is dominated by extragalactic neutrinos. For dark matter of ∼ 1 PeV in mass, we constrain the velocity-averaged annihilation cross section to be smaller than 10 ⁻²³ cm ³ /s for the exclusive μ ⁺ μ ⁻ channel and 10 ⁻²² cm ³ /s for the bb̅ channel. For the same mass, we constrain the lifetime of dark matter to be larger than 10 ²⁸ s for all channels studied, except for decaying exclusively to bb̅ where it is bounded to be larger than 10 ²⁷ s. Finally, we also search for evidence of astrophysical neutrinos scattering on galactic dark matter in two scenarios. For fermionic dark matter with a vector mediator, we constrain the dimensionless coupling associated with this interaction to be less than 0.1 for dark matter mass of 0.1 GeV and a mediator mass of 10 ⁻⁴ GeV. In the case of scalar dark matter with a fermionic mediator, we constrain the coupling to be less than 0.1 for dark matter and mediator masses below 1 MeV.
... In our analysis, we consider exclusively the diffuse neutrino flux, since only for it are measurements of the flavor composition available [25,[31][32][33]. These neutrinos are likely made in extragalactic cosmic-ray accelerators [8,[93][94][95]. Possible candidate source populations [93,95] include active galactic nuclei [96], galaxy clusters [97][98][99][100][101][102], gamma-ray bursts [103][104][105][106][107][108][109], starburst galaxies [110][111][112][113][114][115][116][117], supernovae [118][119][120], and tidal disruption events [121][122][123][124][125][126], among others. ...
A bstract
The discovery of new, flavor-dependent neutrino interactions would provide compelling evidence of physics beyond the Standard Model. We focus on interactions generated by the anomaly-free, gauged, abelian lepton-number symmetries, specifically L e – L μ , L e – L τ , and L μ – L τ , that introduce a new matter potential sourced by electrons and neutrons, potentially impacting neutrino flavor oscillations. We revisit, revamp, and improve the constraints on these interactions that can be placed via the flavor composition of the diffuse flux of high-energy astrophysical neutrinos, with TeV–PeV energies, i.e., the proportion of ν e , ν μ , and ν τ in the flux. Because we consider mediators of these new interactions to be ultra-light, lighter than 10 − 10 eV, the interaction range is ultra-long, from km to Gpc, allowing vast numbers of electrons and neutrons in celestial bodies and the cosmological matter distribution to contribute to this new potential. We leverage the present-day and future sensitivity of high-energy neutrino telescopes and of oscillation experiments to estimate the constraints that could be placed on the coupling strength of these interactions. We find that, already today, the IceCube neutrino telescope demonstrates potential to constrain flavor-dependent long-range interactions significantly better than existing constraints, motivating further analysis. We also estimate the improvement in the sensitivity due to the next-generation neutrino telescopes such as IceCube-Gen2, Baikal-GVD, KM3NeT, P-ONE, and TAMBO.
... In our analysis, we consider exclusively the diffuse neutrino flux, since only for it are measurements of the flavor composition available [25,[32][33][34]. These neutrinos are likely made in extragalactic cosmic-ray accelerators [8,[91][92][93]. Possible candidate source populations [91,93] include active galactic nuclei [94], galaxy clusters [95][96][97][98][99][100], gamma-ray bursts [101][102][103][104][105][106][107], starburst galaxies [108][109][110][111][112][113][114][115], supernovae [116][117][118], and tidal disruption events [119][120][121][122][123][124], among others. ...
The discovery of new, flavor-dependent neutrino interactions would provide compelling evidence of physics beyond the Standard Model. We focus on interactions generated by the anomaly-free, gauged, abelian lepton-number symmetries, specifically , , and , that introduce a new matter potential sourced by electrons and neutrons, potentially impacting neutrino flavor oscillations. We revisit, revamp, and improve the constraints on these interactions that can be placed via the flavor composition of the diffuse flux of high-energy astrophysical neutrinos, with TeV-PeV energies, i.e., the proportion of , , and in the flux. Because we consider mediators of these new interactions to be ultra-light, lighter than eV, the interaction range is ultra-long, from km to Gpc, allowing vast numbers of electrons and neutrons in celestial bodies and the cosmological matter distribution to contribute to this new potential. We leverage the present-day and future sensitivity of high-energy neutrino telescopes and of oscillation experiments to estimate the constraints that could be placed on the coupling strength of these interactions. We find that, already today, the IceCube neutrino telescope demonstrates potential to constrain flavor-dependent long-range interactions significantly better than existing constraints, motivating further analysis. We also estimate the improvement in the sensitivity due to the next-generation neutrino telescopes such as IceCube-Gen2, Baikal-GVD, KM3NeT, P-ONE, and TAMBO.
... The angular distribution of the expected extraterrestrial neutrino induced rate is dependent on the angular distribution of the flux incident on Earth and the Earth's opacity to high-energy neutrinos. The flux incident on the Earth depends on the assumed astrophysical neutrino origin [110]. In this work, we consider two types of incident astrophysical neutrino fluxes: one that is assumed isotropic, and another that is anisotropic and originates from dark matter clustered around the galactic center. ...
In this work, we present the results of searches for signatures of dark matter decay or annihilation into Standard Model particles, and secret neutrino interactions with dark matter. Neutrinos could be produced in the decay or annihilation of galactic or extragalactic dark matter. Additionally, if an interaction between dark matter and neutrinos exists then dark matter will interact with extragalactic neutrinos. In particular galactic dark matter will induce an anisotropy in the neutrino sky if this interaction is present. We use seven and a half years of the High-Energy Starting Event (HESE) sample data, which measures neutrinos in the energy range of approximately 60 TeV to 10 PeV, to study these phenomena. This all-sky event selection is dominated by extragalactic neutrinos. For dark matter of 1 PeV in mass, we constrain the velocity-averaged annihilation cross section to be smaller than cm/s for the exclusive channel and cm/s for the channel. For the same mass, we constrain the lifetime of dark matter to be larger than s for all channels studied, except for decaying exclusively to where it is bounded to be larger than s. Finally, we also search for evidence of astrophysical neutrinos scattering on galactic dark matter in two scenarios. For fermionic dark matter with a vector mediator, we constrain the dimensionless coupling associated with this interaction to be less than 0.1 for dark matter mass of 0.1 GeV and a mediator mass of GeV. In the case of scalar dark matter with a fermionic mediator, we constrain the coupling to be less than 0.1 for dark matter and mediator masses below 1 MeV.
... Pionic gamma rays accompany high-energy neutrinos at the site of production; in fact, their emission rates are intimately related by [183] 1 3 ...
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 (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 νe:νμ:ντ=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 2.87−0.19+0.20 for the 68% confidence interval.
... High-energy astrophysical neutrinos in the TeV-PeV energy range, discovered by the IceCube Neutrino Observatory [1][2][3][4][5][6][7], offer unprecedented insight into astrophysics [6,[8][9][10][11][12] and fundamental physics [13][14][15][16]. On the astrophysical side, they may reveal the identity of the most energetic non-thermal sources in the Universe, located at cosmological-scale distances away from us. ...
We critically examine the ability of future neutrino telescopes, including Baikal-GVD, KM3NeT, P-ONE, TAMBO, and IceCube-Gen2, to determine the flavor composition of high-energy astrophysical neutrinos, ie, the relative number of , , and , in light of improving measurements of the neutrino mixing parameters. Starting in 2020, we show how measurements by JUNO, DUNE, and Hyper-Kamiokande will affect our ability to determine the regions of flavor composition at Earth that are allowed by neutrino oscillations under different assumptions of the flavor composition that is emitted by the astrophysical sources. From 2020 to 2040, the error on inferring the flavor composition at the source will improve from to less than . By 2040, under the assumption that pion decay is the principal production mechanism of high-energy astrophysical neutrinos, a sub-dominant mechanism could be constrained to contribute less than 20\% of the flux at 99.7\% credibility. These conclusions are robust in the nonstandard scenario where neutrino mixing is non-unitary, a scenario that is the target of next-generation experiments, in particular the IceCube-Upgrade. Finally, to illustrate the improvement in using flavor composition to test beyond-the-Standard-Model physics, we examine the possibility of neutrino decay and find that, by 2040, combined neutrino telescope measurements will be able to limit the decay rate of the heavier neutrinos to below ~s, at 95\% credibility.
