Astrophysical Neutrinos Research Articles

Atmospheric neutrinos with the first detection units of KM3NeT/ARCA

The KM3NeT collaboration is constructing two deep-sea Cherenkov detectors in the Mediterranean Sea. The ARCA detector aims at TeV-PeV neutrino astronomy, while the ORCA detector is optimised for atmospheric neutrino oscillation studies at energies of a few GeV. In this contribution, an analysis of the data collected with the first deployed detection units of the ARCA detector is presented. A high-purity sample of atmospheric neutrinos is selected demonstrating the capability of the ARCA detector.

High‐Energy Neutrinos from the Cosmos (Ann. Phys. 11/2021)

Neutrino Astronomy The IceCube Neutrino Observatory is designed to observe the cosmos from deep within the South Pole ice. In article number 2100309, Francis Halzen reviews the results from IceCube's first decade of operations. The cover image illustrates the light pattern recorded by IceCube that is radiated by a particle shower created by the Glashow resonance. Colored dots represent light sensors that detect photons. Their color indicates arrival time, from red (early) to purple (late) following the rainbow, and their size reflects the number of photons detected.

Cosmic rays, neutrinos, and GeV-TeV gamma rays from starburst galaxy NGC 4945

The detection of high-energy astrophysical neutrinos and ultra-high-energy cosmic rays (UHECRs) provides a new way to explore sources of cosmic rays. One of the highest energy neutrino events detected by IceCube, tagged as IC35, is close to the UHECR anisotropy region detected by Pierre Auger Observatory. The nearby starburst (SB) galaxy, NGC 4945, is close to this anisotropic region and inside the mean angular error of the IC35 event. Considering the hypernovae contribution located in the SB region of NGC 4945, which can accelerate protons up to $\ensuremath{\sim}{10}^{17}\text{ }\text{ }\mathrm{eV}$ and inject them into the interstellar medium, we investigate the origin of this event around this starburst galaxy. We show that the interaction of these protons with the SB region's gas density could explain Fermi-LAT gamma-ray and radio observations if the magnetic field's strength in the SB region is the order of $\ensuremath{\sim}\mathrm{mG}$. Our estimated PeV neutrino events, in ten years, for this source is approximately 0.01 ($4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$) if a proton spectral index of 2.4 (2.7) is considered, which would demonstrate that IC35 is not produced in the central region of this SB galaxy. Additionally, we consider the superwind region of NGC 4945 and show that protons can hardly be accelerated in it up to UHECRs.

The IceCube-Gen2 Neutrino Observatory

The IceCube Neutrino Observatory opened the window on neutrino astronomy by discovering high-energy astrophysical neutrinos in 2013 and identifying the first compelling astrophysical neutrino source, the blazar TXS0506 + 056, in 2017. In this proceeding, we will discuss the science reach and ongoing development of the IceCube-Gen2 facility, which is the planned extension to IceCube. IceCube-Gen2 will increase the rate of observed cosmic neutrinos by an order of magnitude, be able to detect five-times fainter neutrino sources, and extend the measurement of astrophysical neutrinos several orders of magnitude higher in energy. We will discuss the envisioned design of the instrument, which will include an enlarged in-ice optical array, a surface array for the study of cosmic-rays, and a shallow radio array to detect ultra-high energy (>100 PeV) neutrinos. We will also highlight ongoing efforts to develop and test new instrumentation for IceCube-Gen2.

Recommended conventions for reporting results from direct dark matter searches

The field of dark matter detection is a highly visible and highly competitive one. In this paper, we propose recommendations for presenting dark matter direct detection results particularly suited for weak-scale dark matter searches, although we believe the spirit of the recommendations can apply more broadly to searches for other dark matter candidates, such as very light dark matter or axions. To translate experimental data into a final published result, direct detection collaborations must make a series of choices in their analysis, ranging from how to model astrophysical parameters to how to make statistical inferences based on observed data. While many collaborations follow a standard set of recommendations in some areas, for example the expected flux of dark matter particles (to a large degree based on a paper from Lewin and Smith in 1995), in other areas, particularly in statistical inference, they have taken different approaches, often from result to result by the same collaboration. We set out a number of recommendations on how to apply the now commonly used Profile Likelihood Ratio method to direct detection data. In addition, updated recommendations for the Standard Halo Model astrophysical parameters and relevant neutrino fluxes are provided. The authors of this note include members of the DAMIC, DarkSide, DARWIN, DEAP, LZ, NEWS-G, PandaX, PICO, SBC, SENSEI, SuperCDMS, and XENON collaborations, and these collaborations provided input to the recommendations laid out here. Wide-spread adoption of these recommendations will make it easier to compare and combine future dark matter results.

Multi-messenger emission from the parsec-scale jet of the flat-spectrum radio quasar PKS 1502+106 coincident with high-energy neutrino IceCube-190730A

On July 30th, 2019 IceCube detected a high-energy astrophysical muon neutrino candidate, IC-190730A with a 67% probability of astrophysical origin. The flat spectrum radio quasar (FSRQ) PKS 1502 +106 is in the error circle of the neutrino. Motivated by this observation, we study PKS 1502+106 as a possible source of IC-190730A. PKS 1502+106 was in a quiet state in terms of UV/optical/X-ray/γ-ray flux at the time of the neutrino alert, we therefore model the expected neutrino emission from the source during its average long-term state, and investigate whether the emission of IC-190730A as a result of the quiet long-term emission of PKS 1502+106 is plausible. We analyse UV/optical and X-ray data and collect additional observations from the literature to construct the multi-wavelength spectral energy distribution of PKS 1502+106. We perform leptohadronic modelling of the multi-wavelength emission of the source and determine the most plausible emission scenarios and the maximum expected accompanying neutrino flux. A model in which the multi-wavelength emission of PKS 1502+106 originates beyond the broad-line region and inside the dust torus is most consistent with the observations. In this scenario, PKS 1502+106 can have produced up to of order one muon neutrino with energy exceeding 100 TeV in the lifetime of IceCube. An appealing feature of this model is that the required proton luminosity is consistent with the average required proton luminosity if blazars power the observed ultra-high-energy-cosmic-ray flux and well below the source's Eddington luminosity. If such a model is ubiquitous among FSRQs, additional neutrinos can be expected from other bright sources with energy ≳ 10 PeV.

Astronomy with energy dependent flavour ratios of extragalactic neutrinos

High energy astrophysical neutrinos interacting with ultralight dark matter (DM) can undergo flavour oscillations that induce an energy dependence in the flavour ratios. Such a dependence on the neutrino energy will reflect in the track to shower ratio in neutrino telescopes like IceCube or KM3NeT. This opens up a possibility to study DM density profiles of astrophysical objects like AGN, GRB etc., which are the suspected sources of such neutrinos.

RES-NOVA sensitivity to core-collapse and failed core-collapse supernova neutrinos

RES-NOVA is a new proposed experiment for the investigation of astrophysical neutrino sources with archaeological Pb-based cryogenic detectors. RES-NOVA will exploit Coherent Elastic neutrino-Nucleus Scattering (CEνNS) as detection channel, thus it will be equally sensitive to all neutrino flavors produced by Supernovae (SNe). RES-NOVA with only a total active volume of (60 cm)3 and an energy threshold of 1 keV will probe the entire Milky Way Galaxy for (failed) core-collapse SNe with > 3 σ detection significance. The high detector modularity makes RES-NOVA ideal also for reconstructing the main parameters (e.g. average neutrino energy, star binding energy) of SNe occurring in our vicinity, without deterioration of the detector performance caused by the high neutrino interaction rate. For the first time, distances <3 kpc can be surveyed, similarly to the ones where all known past galactic SNe happened. We discuss the RES-NOVA potential, accounting for a realistic setup, considering the detector geometry, modularity and background level in the region of interest.We report on the RES-NOVA background model and on the sensitivity to SN neutrinos as a function of the distance travelled by neutrinos.

Modeling the optical Cherenkov signals by cosmic ray extensive air showers directly observed from suborbital and orbital altitudes

Future experiments based on the observation of Earth's atmosphere from sub-orbital and orbital altitudes plan to include optical Cherenkov cameras to observe extensive air showers produced by high-energy cosmic radiation via its interaction with both the Earth and its atmosphere. As discussed elsewhere, particularly relevant is the case of upward-moving showers initiated by astrophysical neutrinos skimming and interacting in the Earth. The Cherenkov cameras, by looking above Earth's limb, can also detect cosmic rays with energies starting from less than a PeV up to the highest energies (tens of EeV). Using a customized computation scheme to determine the expected optical Cherenkov signal from these high-energy cosmic rays, we estimate the sensitivity and event rate for balloon-borne and satellite-based instruments, focusing our analysis on the Extreme Universe Space Observatory aboard a Super Pressure Balloon 2 (EUSO-SPB2) and the Probe of Extreme Multi-Messenger Astrophysics (POEMMA) experiments. We find the expected event rates to be larger than hundreds of events per hour of experimental live time, enabling a promising overall test of the Cherenkov detection technique from sub-orbital and orbital altitudes as well as a guaranteed signal that can be used for understanding the response of the instrument.

Broad-band study of BL Lac during flare of 2020: spectral evolution and emergence of HBL component

ABSTRACT BL Lacertae (BL Lac) is categorized as TeV blazar and considered as a possible source of astrophysical neutrinos. In 2020, the brightest X-ray flare ever detected from it. A detailed study can answer many puzzling questions related to multiband emissions and fast-flux variability often seen in this kind of source. We have performed the temporal and spectral analysis of the brightest flare. The variability is characterized by the fractional variability amplitude and the variability time. We found that the source has crossed all its previous limits of flux and reached to a maximum ever seen from it in optical and X-rays. It is highly variable in X-rays with fractional variability above 100 per cent (1.8397 ± 0.0181) and the fastest variability time of 11.28 h within a day. The broad-band light-curves correlation with X-ray suggest a time lag of one day. A broad-band SED modelling is pursued to understand the possible physical mechanisms responsible for broad-band emission. Modelling requires two emission regions located at two different sites to explain the low and high flux states. A significant spectral change is observed in the optical-UV and X-ray spectrum during the high state, which eventually leads to shifts in the location of the synchrotron peak towards higher energy, suggesting an emergence of a new HBL component.

Astrophysical neutrino source searches with IceCube starting track events

Muons and neutrinos created by cosmic rays interacting in the atmosphere create a significant background for IceCube astrophysical neutrinos in the Southern Sky. However, looking for neutrino events that start in the detector can reduce both the atmospheric muon and atmospheric neutrino background while retaining the astrophysical neutrino signal. The method presented here results in a higher astrophysical neutrino purity for IceCube events at declinations less than -25°. We specifically select for track events, which results in better directional reconstruction due to the long signature the muon leaves in the detector than for cascade events. Due to the improved signal-background ratio and good pointing resolution, we will discuss how this event selection will improve the IceCube sensitivity to southern neutrino sources. We will focus on its impact on searches for galactic plane point sources and diffuse galactic plane neutrino emission. This selection also allows IceCube to send out high astrophysical purity realtime alert events with neutrino energies in the tens of TeV to the multimessenger community.

Constraints on models of the origin of high-energy astrophysical neutrinos

The existence of astrophysical neutrinos with energies of tens of TeV and higher has been firmly established by the IceCube experiment; the first confirmations of this discovery were obtained by the ANTARES and Baikal-GVD installations. At the same time, observational results do not fully agree with those expected before the start of these experiments. The origin of the neutrino has not yet been determined, while simple theoretical models, popular for decades, cannot explain the entire ensemble of observational data. In the present review, a summary of experimental results is given with a particular emphasis on those most relevant for constraining theoretical models; features of various scenarios of the origin of high-energy neutrinos are discussed; and particular classes of their potential astrophysical sources are briefly listed. It is shown that observational data may be explained if the astrophysical neutrino flux includes both a contribution of extragalactic sources, dominant at high energies, and a Galactic component, essential only at neutrino energies ≲ 100 TeV. Other possible scenarios are also discussed.

Starting track events in IceCube

The IceCube Neutrino Observatory is a cubic kilometer-sized detector designed to detect neutrinos of astrophysical origin. We summarize an ongoing dataset that will identify starting track neutrino events above 1 TeV over the entire sky. We discuss a method using a boosted decision tree (BDT) to classify and reduce the cosmic ray muon rates from billions per year to ∼1 per year while selecting ∼1000 starting track events per year. Muon tagging with the BDT also improves our sensitivity to astrophysical neutrinos from the southern sky, since it removes atmospheric neutrinos accompanied by muons from parent cosmic ray showers. Next, we introduce a Random Forest to reconstruct the energy of astrophysical neutrino candidates interacting inside the detector volume, with an energy resolution of 25% made possible by identification of the hadronic and muonic components of the neutrino interaction. Finally, the outgoing muon track is used to reconstruct the direction of the astrophysical neutrino candidates with an estimated median angular resolution of 1.6° at 1 TeV improving to 0.5° at 1 PeV. This dataset will eventually be used to measure the astrophysical diffuse flux, so we summarize the impact of systematic uncertainties on such a measurement.

Constraining the contribution of Gamma-Ray Bursts to the high-energy diffuse neutrino flux with 10 years of ANTARES data

Gamma-Ray Bursts (GRBs) are considered very interesting astrophysical sources to be studied in the context of neutrino astronomy. Indeed, their jet composition continues to be an open issue. Within the framework of the fireball model, mesons can be produced during photo-hadronic interactions occurring in the internal shocks between shells emitted by the central engine. From their decays, high-energy gamma rays and neutrinos are expected to be generated. Neutrino telescopes are particularly interested in GRBs: being the most powerful explosions observable in the Universe, they are potentially able to achieve the energetics required to contribute to the diffuse astrophysical neutrino flux measured few years ago by IceCube. The analysis here presented relies on the search of time and space coincidences between neutrinos and the GRB emission. The undersea neutrino telescope ANTARES, operational in the Northern hemisphere since 2008 in its full configuration, plays an important role in the cosmic neutrino searches. In this contribution, the results of a stacked search for astrophysical muon neutrinos are presented for 784 GRBs in the period 2007-2017 using the ANTARES data. Given the absence of coincidences between a neutrino and a GRB in the considered sample, this analysis has allowed to constrain the contribution of the detected GRB population to the neutrino diffuse flux to be less than 10% around 100 TeV, within the context of the internal shock model. In addition, for the first time in this kind of analysis, the uncertainties on the not well characterised GRB parameters, needed to compute the neutrino flux expectations, are taken into account for each individual burst and then propagated to the diffuse flux from GRBs and to the estimated stacked upper limit.

A self-monitoring precision calibration light source for the IceCube Upgrade

With neutrino astronomy on the rise, calibration aspects of large-volume detectors are becoming one of the key targets to boost detector performance. In the scope of the IceCube Upgrade planned for the South Pole season of 2022/23, we developed a novel, isotropic, self-monitoring, precision calibration light source. We present the device characteristics as well as first studies of calibration impacts for different detection environments.

KM3NeT Detection Unit Line Fit reconstruction using positioning sensors data

The KM3NeT collaboration is constructing two large neutrino detectors in the Mediterranean Sea: ARCA, located near Sicily and aiming at neutrino astronomy, and ORCA, located near Toulon and designed for neutrino oscillation studies. The two detectors, together, will have hundreds of Detection Units (DUs) with 18 Digital Optical Modules (DOMs) maintained vertical by buoyancy, forming a large 3D optical array for detecting the Cherenkov light produced after the neutrino interactions. To properly reconstruct the direction of the incoming neutrino, the position of the DOMs must be known precisely with an accuracy of less than 10 cm. For this purpose, there are acoustic and orientation sensors inside the DOMs. An Attitude Heading Reference System (AHRS) chip provides the components values of the Acceleration and Magnetic field in the DOM, from which it is possible to calculate Yaw, Pitch and Roll for each floor of the line. A piezo sensor detects the signals from fixed acoustic emitters on the sea floor, so as to position it by trilateration. Data from these sensors are used as an input to reconstruct the shape of the entire line based on a DU Line Fit mechanical model. This proceeding presents an overview of the KM3NeT monitoring system, as well as the line fit model and a selection of results.

Estimating the neutrino flux from choked gamma-ray bursts

The strong constraints from the Fermi-LAT data on the isotropic gamma-ray background suggest that the neutrinos observed by IceCube might possibly come from sources that are hidden to gamma-ray observations. A possibility recently discussed in the literature is that neutrinos may come from jets of collapsing massive stars which fail to break out of the stellar envelope, and for this reason they are known as choked jets, or choked Gamma-Ray Bursts (GRBs). In this paper, we estimate the neutrino flux and spectrum expected from these sources, focusing on Type II SNe. We perform detailed calculations of pγ interactions, accounting for all the neutrino production channels and scattering angles. We provide predictions of expected event rates for operating neutrino telescopes, such as ANTARES and IceCube, as well as for the future generation telescope KM3NeT. We find that for GRB energies channeled into protons spanning between ∼ 1051–1053 erg, choked GRBs may substantially contribute to the observed astrophysical neutrino flux, if their local rate is ∼ 80–1 Gpc-3yr-1 respectively.

Double cascade reconstruction in KM3NeT/ARCA

The detection of astrophysical ντ is an important verification of the observed flux of high-energy neutrinos. A flavour ratio of approximately νe : νμ : ντ ≈ 1 : 1 : 1 is predicted for astrophysical neutrinos measured at Earth due to neutrino oscillations. On top of this, the ντ offers a unique channel for neutrino astronomy due to absence of an atmospheric ντ background contribution. When a ντ interacts it produces a particle cascade and often a τ lepton which in turn decays mainly into another cascade. This results in a double cascade signature. An excellent angular resolution can be achieved when both cascade vertices are reconstructed. The KM3NeT/ARCA detector, which is under construction in the Mediterranean sea, will be able to detect this signature due to its timing and spatial resolution for cascades. We will discuss the dedicated reconstruction algorithm and performance for reconstructing double cascades using KM3NeT. The angular deviation reaches sub-degree level for tau lengths larger than 25 meters.

Ограничения на модели происхождения астрофизических нейтрино высоких энергий

The existence of astrophysical neutrinos with energies of tens of TeV and higher has been reliably established by the IceCube experiment; the first confirmations of this discovery are being obtained with the ANTARES and Baikal-GVD facilities. The observational results do not fully agree with what was expected before the start of these experiments. The origin of these neutrinos has not been conclusively established, and simple theoretical models, popular for decades, cannot explain all observational data. This review summarizes the experimental results with emphasis on those important for constraining theoretical models, discusses various scenarios for the origin of high-energy neutrinos and briefly lists particualr classes of their potential astrophysical sources. It is demonstrated that the observational data may be explained if the flux of astrophysical neutrinos includes the contribution of extragalactic sources, dominating at the highest energies, and the Galactic component, significant only at neutrino energies <~100 TeV. Other possible scenarios are also discussed.

Search for high-energy neutrino emission from hard X-ray AGN with IceCube

The IceCube Neutrino Observatory has detected high-energy astrophysical neutrinos in the TeV-PeV range. These neutrinos have an isotropic distribution on the sky, and therefore, likely originate from extragalactic sources. Active Galactic Nuclei form a class of astronomical objects which are promising neutrino source candidates given their high electromagnetic luminosity and potential ability to accelerate cosmic rays up to energies greater than 1016 eV. Interactions of these cosmic rays within the AGN environment are expected to produce both neutrinos and pionic gamma rays. Some hadronic models of AGN emission suggest that such gamma rays can in turn interact with the dense photon fields of AGN and cascade down to hard X-rays and MeV gamma rays. We present an update on the IceCube stacking analysis searching for high-energy neutrinos from hard X-ray sources sampled from the Swift-BAT AGN Spectroscopic Survey.