Astrophysical Flux Research Articles

Cosmic-ray propagation models elucidate the prospects for antinuclei detection

Tentative observations of cosmic-ray antihelium by the AMS-02 collaboration have re-energized the quest to use antinuclei to search for physics beyond the standard model. However, our transition to a data-driven era requires more accurate models of the expected astrophysical antinuclei fluxes. We use a state-of-the-art cosmic-ray propagation model, fit to high-precision antiproton and cosmic-ray nuclei (B, Be, Li) data, to constrain the antinuclei flux from both astrophysical and dark matter annihilation models. We show that astrophysical sources are capable of producing 𝒪(1) antideuteron events and 𝒪(0.1) antihelium-3 events over 15 years of AMS-02 observations. Standard dark matter models could potentially produce higher levels of these antinuclei, but showing a different energy-dependence. Given the uncertainties in these models, dark matter annihilation is still the most promising candidate to explain preliminary AMS-02 results. Meanwhile, any robust detection of antihelium-4 events would require more novel dark matter model building or a new astrophysical production mechanism.

Probing new physics at cosmic dawn with 21-cm cosmology

21-cm cosmology provides an exciting opportunity to probe new physics dynamics in the early universe. In particular, a tiny sub-component of dark matter that interacts strongly with the visible sector may cool the gas in the intergalactic medium and significantly alter the expected absorption signal at Cosmic Dawn. However, the information about new physics in this observable is obscured by astrophysical systematic uncertainties. In the absence of a microscopic framework describing the astrophysical sources, these uncertainties can be encoded in a bottom up effective theory for the 21-cm observables in terms of unconstrained astrophysical fluxes. In this paper, we take a first step towards a careful assessment of the degeneracies between new physics effects and the uncertainties in these fluxes. We show that the latter can be constrained by combining measurements of the UV luminosity function, the Planck measurement of the CMB optical depth to reionization, and an upper bound on the unresolved X-ray flux. Leveraging those constraints, we demonstrate how new physics signatures can be disentangled from astrophysical effects. Focusing on the case of millicharged dark matter, we find sharp predictions, with small uncertainties within the viable parameter space.1

Search for Continuous and Transient Neutrino Emission Associated with IceCube’s Highest-energy Tracks: An 11 yr Analysis

IceCube alert events are neutrinos with a moderate-to-high probability of having astrophysical origin. In this study, we analyze 11 yr of IceCube data and investigate 122 alert events and a selection of high-energy tracks detected between 2009 and the end of 2021. This high-energy event selection (alert events + high-energy tracks) has an average probability of ≥0.5 of being of astrophysical origin. We search for additional continuous and transient neutrino emission within the high-energy events’ error regions. We find no evidence for significant continuous neutrino emission from any of the alert event directions. The only locally significant neutrino emission is the transient emission associated with the blazar TXS 0506+056, with a local significance of 3σ, which confirms previous IceCube studies. When correcting for 122 test positions, the global p-value is 0.156 and compatible with the background hypothesis. We constrain the total continuous flux emitted from all 122 test positions at 100 TeV to be below 1.2 × 10−15 (TeV cm2 s)−1 at 90% confidence assuming an E −2 spectrum. This corresponds to 4.5% of IceCube’s astrophysical diffuse flux. Overall, we find no indication that alert events in general are linked to lower-energetic continuous or transient neutrino emission.

High-energy neutrino astronomy — the neutrino connections to the cosmic-ray origin: present and future

High-energy neutrino astronomy has been blooming. In addition to the possible identification of the blazar and Seyfert II galaxies as neutrino emitters, the present neutrino data has indicated some hints to characterize or constrain the origin of cosmic rays. Being motivated by the observational fact that the astrophysical neutrino background energy flux is comparable to that of ultrahigh-energy (UHE) cosmic rays, we derive the generic requirements that a major fraction of UHE cosmic ray sources must meet, if they are also responsible for the ∼ 100 TeV-energy cosmic neutrino background radiation. The source parameters characterizing the cosmic ray – neutrino unified scheme, such as the photon radiation luminosity and the cosmic ray luminosity density, suggest that the yet-unidentified cosmic ray and neutrino origins can be transient objects visible in the optical/NIR wavelength band. We propose a viable scheme of multimessenger observations to identify the sources using the neutrino multiplet detections.

A new multimessenger study of Starburst galaxies: a closer look to expecting neutrinos

Considering the high star formation rate (up to 100 M⊙/year) of starburst galaxies (SBGs), they are well posed between the guaranteed “factories” of high energy neutrinos, since they can contain accelerated cosmic rays in the central region where the high-density gas is present. A more accurate description of their possible hadronic emission could help to better explain the diffuse astrophysical flux measured by IceCube as well as the observed point-like excess, like the case of NGC1068. With this in mind we report here a multi-messenger study, looking at diffuse and resolved gamma-ray and neutrino measurements, that explain the very-high-energy (VHE) emission through a calorimetric scenario. For the analysis of the diffuse component we perform a blending of the available spectral indexes and produce a multi-component study of extragalactic background light (EGB), high energy starting events (HESE) and high-energy cascade IceCube data. In contrast to common prototype scenarios, the spectral index blending leads to a non negligible diffuse neutrino component from SBGs, accounting up to 40% of the HESE events, at 95.4% CL. This scenario privileges also a maximal energy within tens of PeV for the accelerated charge particles inside these galaxies. For the point-like study we report the proposed calorimetric description for the gamma-ray resolved SBGs within 100 Mpc, taking into account the star formation rate derived from their infrared emission. These neutrino expectations are then compared with the sensitivity of IceCube, IceCube/Gen2 and the incoming KM3NeT.

StarDICE

Context. The Hubble diagram of type-Ia supernovae (SNe-Ia) provides cosmological constraints on the nature of dark energy with an accuracy limited by the flux calibration of currently available spectrophotometric standards. This motivates new developments to improve the link between existing astrophysical flux standards and laboratory standards. Aims. The StarDICE experiment aims to establish a five-stage metrology chain from NIST photodiodes to stars, with a targeted accuracy of 1 mmag in griz colors. We present the first two stages, resulting in the calibration transfer from NIST photodiodes to a demonstration 150 mpixel CMOS sensor (Sony IMX411ALR as implemented in the QHY411M camera by QHYCCD). As a side-product, we provide full characterization of this camera, which we believe to be of potential interest in astronomical imaging and photometry and specifically discuss its use in the context of gravitational wave optical follow-up. Methods. A fully automated spectrophotometric bench was built to perform the calibration transfer. The sensor readout electronics was studied using thousands of flat-field images from which we derived stability, high-resolution photon transfer curves (PTC), and estimates of the individual pixel gain. The sensor quantum efficiency (QE) was then measured relatively to a NIST-calibrated photodiode, in a well-defined monochromatic light beam from 375 to 1078 nm. Last, flat-field scans at 16 different wavelengths were used to build maps of the sensor response, fully characterizing the sensor for absolute photometric measurements. Results. We demonstrated statistical uncertainty on QE below 0.001 e−/γ between 387 nm and 950 nm, the range being limited by the sensitivity decline of the tested sensor in the infrared. Systematic uncertainties in the bench optics are controlled at the level of 1 × 10−3 e−/γ. Linearity issues are detected at the level of 5 × 10−3 e−/γ for the tested camera and require further developments to fully correct. Uncertainty in the overall normalization of the QE curve (without relevance for the cosmology, but relevant to evaluate the performance of the camera itself) is 1%. Regarding the camera we demonstrate stability in steady state conditions at the level of 32.5 ppm. Homogeneity in the response is below 1% RMS across the entire sensor area. Quantum efficiency stays above 50% in most of the visible range, peaking well above 80% between 440 nm and 570 nm. Differential nonlinearities at the level of 1% are detected. A simple two-parameter model is proposed to mitigate the effect and found to adequately correct the shape of the PTC on half the numerical scale. No significant deviations from integral linearity were detected in our limited test. Static and dynamical correlations between pixels are low, making the device likely suitable for galaxy shape measurements.

Multi-messenger high-energy signatures of decaying dark matter and the effect of background light

The IceCube Neutrino Observatory at the South Pole has measured astrophysical neutrinos using through-going and starting events in the TeV to PeV energy range. The origin of these astrophysical neutrinos is still largely unresolved, and among their potential sources could be dark matter decay. Measurements of the astrophysical flux using muon neutrinos are in slight tension with starting event measurements. This tension is driven by an excess observed in the energy range of 40–200 TeV with respect to the through-going expectation. Previous works have considered the possibility that this excess may be due to heavy dark matter decay and have placed constraints using gamma-ray and neutrino data. However, these constraints are not without caveats, since they rely on the modeling of the astrophysical neutrino flux and the sources of gamma-ray emission. In this work, we derive background-agnostic galactic and extragalactic constraints on decaying dark matter by considering Tibet-ASγ data, Fermi-LAT diffuse data, and the IceCube high-energy starting event sample. For the gamma-ray limits, we investigate the uncertainties on secondary emission from electromagnetic cascades during propagation arising from the unknown intensity of the extragalactic background light. We find that such uncertainties amount to a variation of up to ∼ 55% in the gamma-ray limits derived with extragalactic data. Our results imply that a significant fraction of the astrophysical neutrino flux could be due to dark matter and that ruling it out depends on the assumptions on the gamma-ray and neutrino background. The latter depends on the yet unidentified sources.

High-Energy Extragalactic Neutrino Astrophysics

The detection of an astrophysical flux of neutrinos in the TeV–PeV energy range by the IceCube Neutrino Observatory has opened new possibilities for the study of extreme cosmic accelerators. The apparent isotropy of the neutrino arrival directions favors an extragalactic origin for this flux, potentially created by a large population of distant sources. Recent evidence for the detection of neutrino emission from extragalactic sources includes the active galaxies TXS 0506+056 and NGC 1068. We here review the current status of the search for the sources of the high-energy neutrino flux, concentrating on its extragalactic contribution. We discuss the implications of these observations for multimessenger studies of cosmic sources and present an outlook for how additional observations by current and future instruments will help address fundamental questions in the emerging field of high-energy neutrino astronomy.

Multi-messenger lifetime constraints on heavy decaying dark matter

Ultra-high-energy (UHE) neutrino and gamma-ray measurements will help on the dark matter (DM) quest via indirect detection. In this work we used UHE measurements of the astrophysical gamma-ray flux and we forecasted the performance of the future radio neutrino telescopes in order to see the potential limits that they could place on the lifetime of DM particles. We focused in the range of DM masses m DM = [107 — 1015] GeV. We provide the current gamma-ray limits placed by the different experimental collaborations CASA-MIA, KASCADE KASCADE-Grande, Pierre Auger Observatory, Telescope Array and EAS-MSU. We also compare this limits with the projected UHE neutrino ones from future radio neutrino telescopes in order to see the complementarity between both messengers. For a more detailed description of the analysis we refer the reader to [1, 2, 3].

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.

Contribution of Secondary Neutrinos from Line-of-sight Cosmic-Ray Interactions to the IceCube Diffuse Astrophysical Flux

Abstract In 10 years of observations, the IceCube neutrino observatory has revealed a neutrino sky in tension with previous expectations for neutrino point-source emissions. Astrophysical objects associated with hadronic processes might act as production sites for neutrinos, observed as point sources at Earth. Instead, a nearly isotropic flux of astrophysical neutrinos is observed up to PeV energies, prompting a reassessment of the assumed transport and production physics. This work applies a new physical explanation for neutrino production from populations of active galactic nuclei and starburst galaxies to three years of public IceCube point-source data. Specifically, cosmic rays produced at such sources might interact with extragalactic background light and gas along the line of sight, generating a secondary neutrino flux. This model is tested alongside a number of typical flux weighting schemes, in all cases the all-sky flux contribution being constrained to percent levels of the reported IceCube diffuse astrophysical flux.

Detection of a particle shower at the Glashow resonance with IceCube.

The Glashow resonance describes the resonant formation of a W- boson during the interaction of a high-energy electron antineutrino with an electron1, peaking at an antineutrino energy of 6.3petaelectronvolts (PeV) in the rest frame of the electron. Whereas this energy scale is out of reach for currently operating and future planned particle accelerators, natural astrophysical phenomena are expected to produce antineutrinos with energies beyond the PeV scale. Here we report the detection by the IceCube neutrino observatory of a cascade of high-energy particles (a particle shower) consistent with being created at the Glashow resonance. A shower with an energy of 6.05±0.72PeV (determined from Cherenkov radiation in the Antarctic Ice Sheet) was measured. Features consistent with the production of secondary muons in the particle shower indicate the hadronic decay of a resonant W- boson, confirm that the source is astrophysical and provide improved directional localization. The evidence of the Glashow resonance suggests the presence of electron antineutrinos in the astrophysical flux, while also providing further validation of the standard model of particle physics. Its unique signature indicates a method of distinguishing neutrinos from antineutrinos, thus providing a way to identify astronomical accelerators that produce neutrinos via hadronuclear or photohadronic interactions, with or without strong magnetic fields. As such, knowledge of both the flavour (that is, electron, muon or tau neutrinos) and charge (neutrino or antineutrino) will facilitate the advancement of neutrino astronomy.

Observable features in ultrahigh energy neutrinos due to active-sterile secret interactions

We consider the effects of active-sterile secret neutrino interactions, mediated by a new pseudoscalar particle, on high- and ultra high-energy neutrino fluxes. In particular, we focus on the case of 3 active and 1 sterile neutrino coupled by a flavor dependent interaction, extending the case of 1 active and 1 sterile neutrino we have recently examined. We find that, depending on the kind of interaction of sterile neutrino with the active sector, new regions of the parameter space for secret interactions are now allowed leading to interesting phenomenological implications on two benchmark fluxes we consider, namely an astrophysical power law flux, in the range below 100 PeV, and a cosmogenic flux, in the Ultrahigh energy range. First of all, the final active fluxes can present a measurable depletion observable in future experiments. Especially, in the case of only tau neutrino interacting, we find that the effects on the astrophysical power law flux can be so large to be already probed by the IceCube experiment. Moreover, we find intriguing features in the energy dependence of the flavor ratio.

Distinguishing Dirac and Majorana neutrinos with astrophysical fluxes

Massive neutrinos can have helicity . Neutrino helicity changes when the neutrino interacts with an external magnetic field and it is possible that the left-handed neutrinos born inside the Sun or a supernova could leave their sources with a different helicity. Since Dirac and Majorana neutrinos have different cross sections in the scattering of electrons for different neutrino helicities, a change in the final neutrino helicity may generate a different number of events and spectra in terrestrial detectors when astrophysical neutrinos have traveled through regions with strong magnetic fields. In this work, we show that in looking for these effects in solar neutrinos, it could be possible to set bounds in the neutrino properties such as the neutrino magnetic moment. Furthermore, for neutrinos coming from a supernova, we show that even in the case of an extremely small neutrino magnetic moment, μν ∼ 10−19μB, there could be measurable differences in both the number of events and in the spectra of Majorana and Dirac neutrinos as soon as accurate supernova models reduce uncertainties in the neutrino flux predictions.

Update on decaying and annihilating heavy dark matter with the 6-year IceCube HESE data

In view of the IceCube's 6-year high-energy starting events (HESE) sample, we revisit the possibility that the updated data may be better explained by a combination of neutrino fluxes from dark matter decay and an isotropic astrophysical power-law than purely by the latter. We find that the combined two-component flux qualitatively improves the fit to the observed data over a purely astrophysical one, and discuss how these updated fits compare against a similar analysis done with the 4-year HESE data. We also update fits involving dark matter decay via multiple channels, without any contribution from the astrophysical flux. We find that a DM-only explanation is not excluded by neutrino data alone. Finally, we also consider the possibility of a signal from dark matter annihilations and perform analogous analyses to the case of decays, commenting on its implications.

Monitoring and Multi-Messenger Astronomy with IceCube

IceCube currently is the largest neutrino observatory with an instrumented detection volume of 1 km3 buried in the ice-sheet close to the antarctic South Pole station. With a 4 π field of view and an up-time of >99%, it is continuously monitoring the full sky to detect astrophysical neutrinos. With the detection of an astrophysical neutrino flux in 2013, IceCube opened a new observation window to the non-thermal Universe. The IceCube collaboration has a large program to search for astrophysical neutrinos, including measurements of the energy spectrum of the diffuse astrophysical flux, auto- and cross-correlation studies with other multi-messenger particles, and a real-time alert and follow-up system. On 22 September 2017, the IceCube online system sent out an alert reporting a high-energy neutrino event. This alert triggered a series of multi-wavelength follow-up observations that revealed a spatially-coincident blazar TXS 0506+056, which was also in an active flaring state. This correlation was estimated at a 3 σ level. Further observations confirmed the flaring emission in the very-high-energy gamma-ray band. In addition, IceCube found an independent 3.5 σ excess of a time-variable neutrino flux in the direction of TXS 0506+056 two years prior to the alert by examining 9.5 years of archival neutrino data. These are the first multi-messenger observations of an extra-galactic astrophysical source including neutrinos since the observation of the supernova SN1987A. This review summarizes the different detection and analysis channels for astrophysical neutrinos in IceCube, focusing on the multi-messenger program of IceCube and its major scientific results.

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

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 at 1 TeV and improves to sim 0.3^circ 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% assuming an E^{-2} spectrum. The sensitivity on the muon-neutrino flux is at a level of E^2 mathrm {d} N /mathrm {d} E = 3cdot 10^{-13},mathrm {TeV},mathrm {cm}^{-2},mathrm {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.

Constraints on Minute-Scale Transient Astrophysical Neutrino Sources.

High-energy neutrino emission has been predicted for several short-lived astrophysical transients including gamma-ray bursts (GRBs), core-collapse supernovae with choked jets, and neutron star mergers. IceCube's optical and x-ray follow-up program searches for such transient sources by looking for two or more muon neutrino candidates in directional coincidence and arriving within 100s. The measured rate of neutrino alerts is consistent with the expected rate of chance coincidences of atmospheric background events and no likely electromagnetic counterparts have been identified in Swift follow-up observations. Here, we calculate generic bounds on the neutrino flux of short-lived transient sources. Assuming an E^{-2.5} neutrino spectrum, we find that the neutrino flux of rare sources, like long gamma-ray bursts, is constrained to <5% of the detected astrophysical flux and the energy released in neutrinos (100GeV to 10PeV) by a median bright GRB-like source is <10^{52.5} erg. For a harder E^{-2.13} neutrino spectrum up to 30% of the flux could be produced by GRBs and the allowed median source energy is <10^{52} erg. A hypothetical population of transient sources has to be more common than 10^{-5} Mpc^{-3} yr^{-1} (5×10^{-8} Mpc^{-3} yr^{-1} for the E^{-2.13} spectrum) to account for the complete astrophysical neutrino flux.

Analysis of High Energy Starting Events with the KM3NeT/ARCA detector

KM3NeT is a research infrastructure housing the next generation neutrino detectors in the depths of the Mediterranean Sea. The ARCA detector, which is currently under construction, is optimized for neutrino searches from astrophysical sources as well as measurements of the diffuse high energy astrophysical flux. The unambiguous detection of neutrinos of extraterrestrial origin by IceCube has led to the first measurement of a high energy astrophysical neutrino flux. The cutting-edge technology used for the design and construction of KM3NeT Digital Optical Modules along with the properties of sea water allow for a measurement of the neutrino direction with an unpresidented resolution for both track and cascade events. Taking advantage of this angular resolution a method to differentiate track and shower events and a method to reject the atmospheric muon background from track-like events were developed and combined to select a sample of high energy starting events. An analysis for the discovery potential of KM3NeT/ARCA for a diffuse astrophysical neutrino flux using these events is presented.

Use of ANTARES and IceCube Data to Constrain a Single Power-law Neutrino Flux

Abstract We perform the first statistical combined analysis of the diffuse neutrino flux observed by ANTARES (nine-year) and IceCube (six-year) by assuming a single astrophysical power-law flux. The combined analysis reduces by a few percent the best-fit values for the flux normalization and the spectral index. Both data samples show an excess in the same energy range (40–200 TeV), suggesting the presence of a second component. We perform a goodness-of-fit test to scrutinize the null assumption of a single power-law, scanning different values for the spectral index. The addition of the ANTARES data reduces the p-value by a factor . In particular, a single power-law component in the neutrino flux with the spectral index deduced by the six-year up-going muon neutrinos of IceCube is disfavored with a p-value smaller than 10−2.