TeV Neutrinos Research Articles

Possible contributions of two nearby blazars to the NGC 4151 neutrino hotspot

The origin of the high-energy astrophysical neutrinos discovered by IceCube remains unclear, with both blazars and Seyfert galaxies emerging as potential sources. Recently, the IceCube Collaboration reported a $ ∼ σ$ neutrino signal from the direction of the nearby Seyfert galaxy NGC 4151. However, two gamma-ray-loud BL Lac objects, 4FGL 1210.3+3928 and 4FGL J1211.6+3901, lie close to NGC 4151, at angular distances of 0.08^∘ and 0.43^∘, respectively. We investigated the potential contribution of these two blazars to the observed neutrino signal from the direction of NGC 4151 and assessed their detectability with future neutrino observatories. We modeled the multiwavelength spectral energy distributions (SEDs) of both blazars using a self-consistent numerical radiation code, AM^3. We calculated their neutrino spectra and compared them to the measured NGC 4151 neutrino spectrum and future neutrino detector sensitivities. The SED of 4FGL 1210.3+3928 revealed a feature that cannot be explained with a purely leptonic model, suggesting the presence of protons in the jet. Our model predicts neutrino emission peaking above ∼10^17 eV with fluxes of $ ∼ erg cm^ s^ $ for this source. The SED of 4FGL J1211.6+3901 can be explained with both leptonic and leptohadronic models. The contribution of these two blazars to the ∼10 TeV neutrino signal observed from the direction of NGC 4151 can only be minor. Still, future radio-based neutrino telescopes such as IceCube-Gen2's radio array and GRAND may be able to detect high-energy neutrinos from these two potential neutrino sources.

A Magnetized Strongly Turbulent Corona as the Source of Neutrinos from NGC 1068

The cores of active galactic nuclei are potential accelerators of 10–100 TeV cosmic rays, in turn producing high-energy neutrinos. This picture was confirmed by the compelling evidence of a TeV neutrino signal from the nearby active galaxy NGC 1068, leaving open the question of what is the site and mechanism of cosmic-ray acceleration. One candidate is the magnetized turbulence surrounding the central supermassive black hole. Recent particle-in-cell simulations of magnetized turbulence indicate that stochastic cosmic-ray acceleration is nonresonant, in contrast to the assumptions of previous studies. We show that this has important consequences on a self-consistent theory of neutrino production in the corona, leading to a more rapid cosmic-ray acceleration than previously considered. The turbulent magnetic-field fluctuations needed to explain the neutrino signal are consistent with a magnetically powered corona. We find that strong turbulence, with turbulent magnetic energy density higher than 1% of the rest-mass energy density, naturally explains the normalization of the IceCube neutrino flux, in addition to the neutrino spectral shape. Only a fraction of the protons in the corona, which can be directly inferred from the neutrino signal, are accelerated to high energies. Thus, in this framework, the neutrino signal from NGC 1068 provides a testbed for particle acceleration in magnetized turbulence.

Towards multi-messenger observations of core-collapse supernovae harbouring choked jets

Context. Over the past decade, choked jets have attracted particular attention as potential sources of high-energy cosmic neutrinos. It is challenging to test this hypothesis because of the missing gamma-ray counterpart. An identification of other electromagnetic signatures is therefore crucial. Extended H envelopes surrounding collapsing massive stars might choke launched jets. In addition, the same progenitors are expected to produce a shock-breakout signal in the ultraviolet (UV) and optical that lasts several days. Early UV radiation in particular carries important information about the presence and nature of choked jets. Aims. While UV observations of core-collapse supernovae have so far been limited, the full potential of observations in this spectral band will soon be transformed by the ULTRASAT satellite mission with its unprecedented field of view. We investigated the detection prospects of choked jet progenitors by ULTRASAT in relation to their visibility in the optical band by the currently operating telescope ZTF. In addition, as choked jets can produce neutrinos via hadronic and photohadronic interactions in choked jets, we also investigated how neutrino observations by existing Cherenkov high-energy neutrino telescopes (e.g. IceCube and KM3NeT) can be used in association with electromagnetic signals from shock-breakout events. Methods. By considering fiducial parameters of the source population and instrument performances, we estimated the maximum redshift up to which ULTRASAT and ZTF are able to detect ultraviolet and optical signals from these explosions, respectively. Furthermore, we discuss coordinated multi-messenger observations using ULTRASAT, ZTF, and high-energy neutrino telescopes. Results. We find that ULTRASAT will double the volume of the sky that is currently visible by ZTF for the same emitting sources. This will enlarge the sample of observed Type II supernovae by ∼60%. For optimised multi-messenger detections, the delay between neutrinos produced at the shock breakout (during the jet propagation inside the stellar envelope) and ULTRASAT observations should be of ∼4 (5) days, with subsequent follow-up by instruments such as ZTF about one week later. We estimate that fewer than 1% of the core-collapse supernovae from red supergiant stars that are detectable in UV with ULTRASAT might host a choked jet and release TeV neutrinos. Electromagnetic and neutrino detections, if accompanied by additional photometric and spectroscopic follow-up with compelling evidence for a relativistic jet launched by the central engine of the source, would suggest that core-collapse supernovae harbouring choked jets are the main contributors to the diffuse astrophysical high-energy neutrino flux.

Hadronuclear Interactions in Active Galactic Nuclei Jets as the Origin of the Diffuse High-energy Neutrino Background

The origin of diffuse high-energy neutrinos from TeV to PeV energies detected by the IceCube Observatory remains a mystery. In our previous work, we have shown that hadronuclear (p − p) interactions in active galactic nuclei (AGNs) jets could be important and generate detectable very-high-energy emissions. Here, we further explore these interactions in the AGN jets based on their luminosity function. The diffuse neutrino flux and corresponding γ-ray flux have been calculated and compared with observational data. In our modeling, two beaming patterns are considered separately. To make sure that the corresponding γ-ray flux does not overshoot the diffuse γ-ray background, we find that if the neutrino production region in a jet is opaque to γ-rays, p − p interactions in AGN jets with a small viewing angle (the blazar case) are able to interpret the PeV neutrino background. Similarly, AGN jets with a large viewing angle (the radio galaxy case) may interpret the TeV neutrino background. While, if the neutrino production region is transparent to γ-rays, only blazars have the potential to interpret the diffuse neutrino background around the PeV band. Some caveats are also discussed.

Differential Sensitivity of the KM3NeT/ARCA detector to a diffuse neutrino flux and to point-like source emission: Exploring the case of the Starburst Galaxies

KM3NeT/ARCA is a Cherenkov neutrino telescope under construction in the Mediterranean sea, optimised for the detection of astrophysical neutrinos with energies above ∼1 TeV. In this work, using Monte Carlo simulations including all-flavour neutrinos, the integrated and differential sensitivities for KM3NeT/ARCA are presented considering the case of a diffuse neutrino flux as well as extended and point-like neutrino sources. This analysis is applied to Starburst Galaxies demonstrating that the detector has the capability of tracing TeV neutrinos from these sources. Remarkably, after eight years, a hard power-law spectrum from the nearby Small Magellanic Cloud can be constrained. The sensitivity and discovery potential for NGC 1068 is also evaluated showing that KM3NeT/ARCA will discriminate between different astrophysical components of the measured neutrino flux after 3 years of data taking.

A stacked search for spatial coincidences between IceCube neutrinos and radio pulsars

We carry out a stacked search for spatial coincidences between all the known radio pulsars and TeV neutrinos from the IceCube 10 year (2008–2018) muon track data, as a followup to our previous work on searching for spatial coincidences with individual pulsars. We consider three different weighting schemes to stack the contributions from each pulsar. We do not find a statistically significant excess using this method. We report the 95% c.l. neutrino flux upper limit as a function of the neutrino energy. We have also made our analysis codes publicly available.

The neutrino background from non-jetted active galactic nuclei

Aims. We calculate the contribution to the neutrino background from the non-jetted active galactic nuclei (AGN) population following the recent IceCube association of TeV neutrinos with NGC 1068. Methods. We exploited our robust knowledge of the AGN X-ray luminosity function and evolution and converted it to the neutrino band by using NGC 1068 as a benchmark, together with a theoretically motivated neutrino spectrum. Results. The resulting neutrino background up to redshift 5 does not violate either the IceCube diffuse flux or the upper bounds for non-jetted AGN, although barely so. This is consistent with a scenario in which the latter class makes a substantial contribution mostly below 1 PeV, while jetted AGN, that is, blazars, dominate above this energy, in intriguing agreement with the dip in the neutrino data at ∼300 TeV. More and better IceCube data on Seyfert galaxies will allow us to constrain the fraction of neutrino emitters among non-jetted AGN.

TeV Neutrinos and Hard X-Rays from Relativistic Reconnection in the Corona of NGC 1068

The recent discovery of astrophysical neutrinos from the Seyfert galaxy NGC 1068 suggests the presence of nonthermal protons within a compact “coronal” region close to the central black hole. The acceleration mechanism of these nonthermal protons remains elusive. We show that a large-scale magnetic reconnection layer, of the order of a few gravitational radii, may provide such a mechanism. In such a scenario, rough energy equipartition between magnetic fields, X-ray photons, and nonthermal protons is established in the reconnection region. Motivated by recent 3D particle-in-cell simulations of relativistic reconnection, we assume that the spectrum of accelerated protons is a broken power law, with the break energy being constrained by energy conservation (i.e., the energy density of accelerated protons is at most comparable to the magnetic energy density). The proton spectrum is dnp/dEp∝Ep−1 below the break and dnp/dEp∝Ep−s above the break, with IceCube neutrino observations suggesting s ≃ 3. Protons above the break lose most of their energy within the reconnection layer via photohadronic collisions with the coronal X-rays, producing a neutrino signal in good agreement with the recent observations. Gamma rays injected in photohadronic collisions are cascaded to lower energies, sustaining the population of electron–positron pairs that makes the corona moderately Compton thick.

Setting an upper limit for the total TeV neutrino flux from the disk of our Galaxy

We set an upper limit for the total TeV neutrino flux expected from the disk of our Galaxy in the region |l| < 30° and |b| < 2° probed by the ANTARES experiment.We include both the diffuse emission, due to the interaction of cosmic rays with the interstellar medium, and the possible contribution produced by gamma-ray Galactic sources.The neutrino diffuse emission is calculated under different assumptions for the cosmic ray spatial and energy distribution in our Galaxy.The source contribution is instead constrained by analysis of the gamma-ray TeV sources included in the H.G.P.S. catalog.In particular, we assume that the total gamma-ray flux produced by all the sources, resolved and unresolved by H.E.S.S., is produced via hadronic interaction and, hence, is coupled with neutrino emission.We compare our total neutrino flux with the recent ANTARES measurement of the neutrino from the Galactic Ridge.We show that the ANTARES best-fit flux requires the existence of a large source component, close to or even larger than the most optimistic predictions obtained with our approach.

Hint for a TeV neutrino emission from the Galactic Ridge with ANTARES

Interactions of cosmic ray protons, atomic nuclei, and electrons in the interstellar medium in the inner part of the Milky Way produce a γ-ray flux from the Galactic Ridge. If the γ-ray emission is dominated by proton and nuclei interactions, a neutrino flux comparable to the γ-ray flux is expected from the same sky region.Data collected by the ANTARES neutrino telescope are used to constrain the neutrino flux from the Galactic Ridge in the 1-100 TeV energy range. Neutrino events reconstructed both as tracks and showers are considered in the analysis and the selection is optimized for the search of an excess in the region |l|<30°, |b|<2°. The expected background in the search region is estimated using an off-zone region with similar sky coverage. Neutrino signal originating from a power-law spectrum with spectral index ranging from Γν=1 to 4 is simulated in both channels. The observed energy distributions are fitted to constrain the neutrino emission from the Ridge.The energy distributions in the signal region are inconsistent with the background expectation at ∼96% confidence level. The mild excess over the background is consistent with a neutrino flux with a power law with a spectral index 2.45−0.34+0.22 and a flux normalization dNνdEν=4.0−2.0+2.7×10−16 GeV−1cm−2s−1sr−1 at 40 TeV reference energy. Such flux is consistent with the expected neutrino signal if the bulk of the observed γ-ray flux from the Galactic Ridge originates from interactions of cosmic ray protons and nuclei with a power-law spectrum extending well into the PeV energy range.

MeV, GeV and TeV Neutrinos from Binary-Driven Hypernovae

We analyze neutrino emission channels in energetic (≳1052 erg) long gamma-ray bursts within the binary-driven hypernova model. The binary-driven hypernova progenitor is a binary system composed of a carbon-oxygen star and a neutron star (NS) companion. The gravitational collapse leads to a type Ic supernova (SN) explosion and triggers an accretion process onto the NS. For orbital periods of a few minutes, the NS reaches the critical mass and forms a black hole (BH). Two physical situations produce MeV neutrinos. First, during the accretion, the NS surface emits neutrino–antineutrino pairs by thermal production. We calculate the properties of such a neutrino emission, including flavor evolution. Second, if the angular momentum of the SN ejecta is high enough, an accretion disk might form around the BH. The disk’s high density and temperature are ideal for MeV-neutrino production. We estimate the flavor evolution of electron and non-electron neutrinos and find that neutrino oscillation inside the disk leads to flavor equipartition. This effect reduces (compared to assuming frozen flavor content) the energy deposition rate of neutrino–antineutrino annihilation into electron–positron (e+e−) pairs in the BH vicinity. We then analyze the production of GeV-TeV neutrinos around the newborn black hole. The magnetic field surrounding the BH interacts with the BH gravitomagnetic field producing an electric field that leads to spontaneous e+e− pairs by vacuum breakdown. The e+e− plasma self-accelerates due to its internal pressure and engulfs protons during the expansion. The hadronic interaction of the protons in the expanding plasma with the ambient protons leads to neutrino emission via the decay chain of π-meson and μ-lepton, around and far from the black hole, along different directions. These neutrinos have energies in the GeV-TeV regime, and we calculate their spectrum and luminosity. We also outline the detection probability by some current and future neutrino detectors.

The Forward Physics Facility at the High-Luminosity LHC

High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe standard model (SM) processes and search for physics beyond the standard model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF’s physics potential.

Neutrino Cadence of TXS 0506+056 Consistent with Supermassive Binary Origin

On 2022 September 18, an alert by the IceCube Collaboration indicated that a ∼170 TeV neutrino arrived in directional coincidence with the blazar TXS 0506+056. This event adds to two previous pieces of evidence that TXS 0506+056 is a neutrino emitter, i.e., a neutrino alert from its direction on 2017 September 22, and a 3σ signature of a dozen neutrinos in 2014/2015. De Bruijn el al. showed that two previous neutrino emission episodes from this blazar could be due to a supermassive binary black hole (SMBBH) central engine where jet precession close to the final coalescence of the binary results in periodic emission. This model predicted a new emission episode consistent with the 2022 September 18 neutrino observation by IceCube. Here, we show that the neutrino cadence of TXS 0506+056 is consistent with an SMBBH origin. We find that the emission episodes are consistent with an SMBBH with mass ratios q ≲ 0.3 for a total black hole mass of M tot ≳ 3 · 108 M ⊙. For the first time, we calculate the characteristic strain of the gravitational wave emission of the binary, and show that the merger could be detectable by LISA for black hole masses <5 · 108 M ⊙ if the mass ratios are in the range 0.1 ≲ q ≲ 0.3. We predict that there can be a neutrino flare existing in the still-to-be-analyzed IceCube data peaking some time between 2019 August and 2021 January if a precessing jet is responsible for all three detected emission episodes. The next flare is expected to peak in the period 2023 January to 2026 August. Further observation will make it possible to constrain the mass ratio as a function of the total mass of the black hole more precisely and would open the window toward the preparation of the detection of SMBBH mergers.

Neutrinos from the Brightest Gamma-Ray Burst?

We discuss implications that can be obtained by searches for neutrinos from the brightest gamma-ray burst (GRB), GRB 221009A. We derive constraints on GRB model parameters such as the cosmic-ray loading factor and dissipation radius, taking into account both neutrino spectra and effective areas. The results are strong enough to constrain proton acceleration near the photosphere, and we find that the single burst limits are comparable to those from stacking analysis. Quasi-thermal neutrinos from subphotospheres and ultra-high-energy neutrinos from external shocks are not yet constrained. We show that GeV–TeV neutrinos originating from neutron collisions are detectable, and urge dedicated analysis on these neutrinos with DeepCore and IceCube as well as ORCA and KM3NeT.

Ultra-high energy cosmic neutrinos from gamma-ray bursts

Based on the recent association of IceCube TeV and PeV neutrino events with gamma-ray bursts (GRBs) by considering the Lorentz violation of neutrinos, we provide a new estimate on the GRB neutrino flux with a more significant result compared to the previous constraint by the IceCube Collaboration. Among these 24 neutrino “shower” events above 60 TeV, 12 events are associated with GRBs. Such a result is compatible with the prediction from GRB fireball models. Analysis of track events provides a consistent result with the shower events to associate high energy cosmic neutrinos with GRBs under the same Lorentz violation features of neutrinos. We also make a background estimation and reveal GRBs as a significant source for the ultra-high energy IceCube neutrino events. Our work supports the Lorentz violation and CPT-violation of neutrinos, indicating new physics beyond relativity.

Parton distribution function uncertainties in theoretical predictions for far-forward tau neutrinos at the Large Hadron Collider

New experiments dealing with neutrinos in the far-forward region at the Large Hadron Collider (LHC) are under design or already in preparation. Two of them, FASERν and SND@LHC, are expected to be active during Run 3 and have the potential to detect the interactions of ν and overline{nu} that come from high-energy collisions in one of the LHC interaction points, extracted along the direction tangent to the beam line. Tau neutrinos and antineutrinos come predominantly from {D}_s^{pm } production in pp collisions, followed by the leptonic decay of these mesons. Neutrino pseudorapidities in the range of η > 6.9 and η > 8.9 are relevant to these future experiments. At such pseudorapidities at high energies, QCD theoretical predictions for the flux of ντ plus overline{nu} τ rely on parton distribution functions (PDFs) in a combination of very small and large parton−x values. We evaluate PDF un certainties affecting the flux of ντ + overline{nu} τ produced by {D}_s^{pm } decay in the far forward region at the LHC. Next-to-leading order (NLO) QCD uncertainties are included in the calculation of {D}_s^{pm } production and NLO PDF sets are used for consistency. The theoretical uncertainty associated with the 40 PDF sets of the PROSA19 group amounts to ±(20 − 30)% for the (ντ + overline{nu} τ) number of charged-current (CC) events. Scale uncertainties are much larger, resulting in a range of CC event predictions from ~70% lower to ~90% higher than the central prediction. A comparison of the predictions with those obtained using as input the central PDFs from the 3-flavour NLO PDF sets of the CT14, ABMP16 and NNPDF3.1 collaborations show that far-forward neutrino energy distributions vary by as much as a factor of ~2 – 4 relative to the PROSA19 predictions at TeV neutrino energies. The Forward Physics Facility in the high luminosity LHC era will provide data capable of constraining NLO QCD evaluations with these PDF sets.

Testing Lorentz Violation with IceCube Neutrinos

Lorentz violation (LV) induced by Quantum Gravity has been tested at much lower energies than the Planck scale with more and more observational evidence. In recent studies, the time of flight difference between the TeV neutrino and MeV photon from Gamma Ray Bursts (GRBs) have been used to constrain the LV energy scale, based on the energy-dependent speed variation. Here, we performed a correlation study between the updated 7.5 year high-energy starting events (HESE), neutrino alert events detected by IceCube, and a full sample of more than 7000 GRBs, and we found six GRB-neutrino candidates, including four alerts and two track events. We obtained the first order energy scale of quantum gravity, namely EQG=8−5+15×1017GeV, which was consistent with other authors‘ work. We suggest that neutrinos and anti-neutrinos can be identified, respectively, due to the delay or advance of the observed time. For future point source search study of neutrinos, the arrival time difference of different particles may have to be taken into account.

High-energy neutrinos from fast winds in novae

ABSTRACT We discuss a scenario in which TeV neutrinos are produced during explosions of novae. It is argued that hadrons are accelerated to very high energies in the inner part of a nova wind, as a result of reconnection of the strong magnetic field of a white dwarf. Hadrons are expected to interact efficiently with a dense matter of the wind, either already during the acceleration process or during their advection with the equatorial wind. We calculate the neutrino spectra and estimate the muon neutrino event rates in the IceCube telescope, in the case of a few novae. In general, those event rates are unlikely to be detected with the present neutrino detectors. However, for a favourable location of the observer, some neutrino events might be detected not only from the class of novae recently detected in the GeV γ-rays by the Fermi-LAT (Large Area Telescope), but also from novae not detected in γ-rays. The GeV γ-ray emission observed from novae cannot originate in terms of the model discussed here, since protons are accelerated within a few stellar radii of the white dwarf, i.e. in the region in which GeV γ-rays are expected to be severely absorbed in the interactions with the radiation field and the matter of the wind.

Observation of Photons above 300 TeV Associated with a High-energy Neutrino from the Cygnus Region

Abstract Galactic sites of acceleration of cosmic rays to energies of order 1015 eV and higher, dubbed PeVatrons, reveal themselves by recently discovered gamma radiation of energies above 100 TeV. However, joint gamma-ray and neutrino production, which marks unambiguously cosmic-ray interactions with ambient matter and radiation, was not observed until now. In 2020 November, the IceCube neutrino observatory reported an ∼150 TeV neutrino event from the direction of one of the most promising Galactic PeVatrons, the Cygnus Cocoon. Here we report on the observation of a 3.1σ (post-trial) excess of atmospheric air showers from the same direction, observed by the Carpet–2 experiment and consistent with a few months flare in photons above 300 TeV, in temporal coincidence with the neutrino event. The fluence of the gamma-ray flare is of the same order as that expected from the neutrino observation, assuming the standard mechanism of neutrino production. This is the first evidence for the joint production of high-energy neutrinos and gamma-rays in a Galactic source.

An interacting molecular cloud scenario for production of gamma-rays and neutrinos from MAGIC J1835-069, and MAGIC J1837-073

Recently the MAGIC telescope observed three TeV gamma-ray extended sources in the galactic plane in the neighborhood of radio SNR G24.7+0.6. Among them, the PWN HESS J1837-069 was detected earlier by the HESS observatory during its first galactic plane survey. The other two sources, MAGIC J1835-069 and MAGIC J1837-073 are detected for the first time at such high energies. Here we shall show that the observed gamma-rays from the SNR G24.7+0.6 and the HESS J1837-069 can be explained in terms of hadronic interactions of the PWN/SNR accelerated cosmic rays with the ambient matter. We shall further demonstrate that the observed gamma-rays from the MAGIC J1837-073 can be interpreted through hadronic interactions of runaway cosmic-rays from PWN HESS J1837-069 with the molecular cloud at the location of MAGIC J1837-073. No such association has been found between MAGIC J1835-069 and SNR G24.7+0.6 or PWN HESS J1837-069. We have examined the maximum energy attainable by cosmic-ray particles in the SNR G24.7+0.6/ PWN HESS J1837-069 and the possibility of their detection with future gamma-ray telescopes. The study of TeV neutrino emissions from the stated sources suggests that the HESS J1837-069 should be detected by IceCube Gen-2 neutrino telescope in a few years of observation.