IceCube Neutrino Observatory Research Articles

Neutrinos below 100 TeV from the southern sky employing refined veto techniques to IceCube data

Many Galactic sources of gamma rays, such as supernova remnants, are expected to produce neutrinos with a typical energy cutoff well below 100 TeV. For the IceCube Neutrino Observatory located at the South Pole, the southern sky, containing the inner part of the Galactic plane and the Galactic Center, is a particularly challenging region at these energies, because of the large background of atmospheric muons. In this paper, we present recent advancements in data selection strategies for track-like muon neutrino events with energies below 100 TeV from the southern sky. The strategies utilize the outer detector regions as veto and features of the signal pattern to reduce the background of atmospheric muons to a level which, for the first time, allows IceCube searching for point-like sources of neutrinos in the southern sky at energies between 100 GeV and several TeV in the muon neutrino charged current channel. No significant clustering of neutrinos above background expectation was observed in four years of data recorded with the completed IceCube detector. Upper limits on the neutrino flux for a number of spectral hypotheses are reported for a list of astrophysical objects in the southern hemisphere.

Cosmic ray spectrum and composition from PeV to EeV using 3 years of data from IceTop and IceCube

We report on measurements of the all-particle cosmic ray energy spectrum and composition in the PeV to EeV energy range using three years of data from the IceCube Neutrino Observatory. The IceTop detector measures cosmic ray induced air showers on the surface of the ice, from which the energy spectrum of cosmic rays is determined by making additional assumptions about the mass composition. A separate measurement is performed when IceTop data are analyzed in coincidence with the high-energy muon energy loss information from the deep in-ice IceCube detector. In this measurement, both the spectrum and the mass composition of the primary cosmic rays are simultaneously reconstructed using a neural network trained on observables from both detectors. The performance and relative advantages of these two distinct analyses are discussed, including the systematic uncertainties and the dependence on the hadronic interaction models, and both all-particle spectra as well as individual spectra for elemental groups are presented.

Constraints on very high energy gamma-ray emission from the Fermi bubbles with future ground-based experiments

The origin of sub-TeV gamma rays detected by the \textit{Fermi}-Large Area Telescope (LAT) from the \textit{Fermi} Bubbles (FBs) at the Galactic center is still uncertain. In a hadronic model, acceleration of protons and/or nuclei and their subsequent interactions with gas in the bubble volume can produce the observed gamma rays. Recently the High Altitude Water Cherenkov (HAWC) observatory reported an absence of gamma-ray excess from the Northern FB at $b\gtrsim 6^\circ$ Galactic latitude, which resulted in flux upper limits in the energy range of $1.2-126$ TeV. These upper limits are consistent with the gamma-ray spectrum measured by \textit{Fermi}-LAT at $|b|\ge 10^\circ$, where an exponential cutoff at energies $\gtrsim 100$ GeV is evident. However, the FB gamma-ray spectrum at $|b|\le 10^\circ$, without showing any sign of cutoff up to around 1 TeV in the latest results, remains unconstrained. The upcoming Cherenkov Telescope Array (CTA) will perform a Galactic center survey with unprecedented sensitivity in the energy between 20 GeV and 300 TeV. In this work, we perform both morphological and classic on/off analyses with planned CTA deep central and extended survey and estimate the sensitivity of CTA to the FB hadronic gamma-ray flux models that best fit the spectrum at $|b|\le 10^\circ$ and whose counterpart neutrino flux model best fits the optimistic neutrino spectrum from IceCube Neutrino Observatory. We also perform sensitivity analysis with a future ground-based Cherenkov detector the Large High Altitude Air Shower Observatory (LHAASO). We find that CTA will be able to discover or constrain the FB gamma-ray flux at $|b|\le 10^\circ$ in the $\approx$ 200 GeV -- 100 TeV range with planned observation strategy, while LHAASO may constrain emission in the $\approx 100$~GeV -- 100~TeV range if $\lesssim 10\%$ systematic uncertainties can be achieved.

Detection of the Temporal Variation of the Sun's Cosmic Ray Shadow with the IceCube Detector

Abstract We report on the observation of a deficit in the cosmic ray flux from the directions of the Moon and Sun with five years of data taken by the IceCube Neutrino Observatory. Between 2010 May and 2011 May the IceCube detector operated with 79 strings deployed in the glacial ice at the South Pole, and with 86 strings between 2011 May and 2015 May. A binned analysis is used to measure the relative deficit and significance of the cosmic ray shadows. Both the cosmic ray Moon and Sun shadows are detected with high statistical significance (>10σ) for each year. The results for the Moon shadow are consistent with previous analyses and verify the stability of the IceCube detector over time. This work represents the first observation of the Sun shadow with the IceCube detector. We show that the cosmic ray shadow of the Sun varies with time. These results make it possible to study cosmic ray transport near the Sun with future data from IceCube.

Measurement of atmospheric tau neutrino appearance with IceCube DeepCore

We present a measurement of atmospheric tau neutrino appearance from oscillations with three years of data from the DeepCore sub-array of the IceCube Neutrino Observatory. This analysis uses atmospheric neutrinos from the full sky with reconstructed energies between 5.6 GeV and 56 GeV to search for a statistical excess of cascade-like neutrino events which are the signature of nutau interactions. For CC+NC (CC-only) interactions, we measure the tau neutrino normalization to be 0.73 +0.30 -0.24 (0.57 +0.36 -0.30) and exclude the absence of tau neutrino oscillations at a significance of 3.2 sigma (2.0 sigma) These results are consistent with, and of similar precision to, a confirmatory IceCube analysis also presented, as well as measurements performed by other experiments.

IceCube High Energy Starting Events at 7.5 Years - New Measurements of Flux and Flavor

The IceCube Neutrino Observatory at the South Pole, which detects Cherenkov light from charged particles produced in neutrino interactions, firmly established the existence of an astrophysical high-energy neutrino component. Here I present IceCube’s High-Energy Starting Event sample and the new results obtained with a livetime of about 7.5 years. I will focus on the new measurement of the flavor composition performed using this sample. IceCube is directly sensitive to each neutrino flavor via the single cascade, track and double cascade event topologies, the latter being the topology produced in tauneutrino interactions above an energy threshold of ~100 TeV. A measurement of the flavor ratio on Earth can provide important constraints on sources and production mechanisms within the standard model, and also constrain various beyond-standard-model processes.

The multi-PMT optical module for the IceCube-Upgrade

Following the first observation of an astrophysical high-energy neutrino flux with the IceCube Neutrino Observatory in 2013, planning for an upgrade of the detector is progressing, which will expand the capabilities of the detector both at low and high neutrino energies. A substantial contribution to the improved performance is anticipated to be achieved by the application of advanced optical module technology. The multi-PMT optical module, mDOM, consists of 24 3-inch PMTs which provide, amongst others, a large, homogeneous photosensitive area and sensitivity to the incident direction of photons. After an introduction, the current status of the mDOM development is presented with emphasis on the characterization of the photomultipliers under consideration.

Search for correlations of high-energy neutrinos and ultrahigh- energy cosmic rays

The IceCube Neutrino Observatory has recently found compelling evidence for a particular blazar producing high-energy neutrinos and PeV cosmic rays, however the sources of cosmic rays above several EeV remain unidentified. It is believed that the same environments that accelerate ultra-high-energy cosmic rays (UHECRs) also produce high-energy neutrinos via hadronic interactions of lower-energy cosmic rays. Two out of three joint analyses of the Ice- Cube Neutrino Observatory, the Pierre Auger Observatory and the Telescope Array yielded hints for a possible directional correlation of high-energy neutrinos and UHECRs. These hints however became less significant with more data. Recently, an improved analysis with an approach complementary to the other analyses has been developed. This analysis searches for neutrino point sources in the vicinity of UHECRs with search windows estimated from deflections by galactic magnetic fields. We present this new analysis method for searching common hadronic sources, additionally including neutrino data measured by ANTARES in order to increase the sensitivity to possible correlations in the Southern Hemisphere.

Searching for Optical Counterparts to High-Energy Neutrino Sources with the Zwicky Transient Facility

The IceCube neutrino observatory has discovered a flux of extragalactic neutrinos. However, the origin of these neutrinos is still unknown. Among the possible candidates are Gamma-Ray Bursts (GRBs), Core-Collapse Supernovae (SNe), Active Galactic Nuclei (AGN) and Tidal Disruption Events (TDEs) - all are accompanied by a characteristic optical counterpart. The goal of this study is thus to identify the neutrino sources by detecting their optical counterparts with the Zwicky Transient Facility (ZTF). ZTF features a high cadence northern-sky survey enabling realtime correlation of optical transients with high-energy neutrino candidates. In this talk I will highlight the multimessenger potential of ZTF for an online neutrino correlation study with Ice- Cube.

Latest Cosmic Ray Results from IceTop and IceCube

The IceCube Neutrino Observatory at the geographic South Pole, with its surface array IceTop, detects three different components of extensive air showers: the total signal at the surface, low energy muons on the periphery of the showers, and high energy muons in the deep In Ice array of IceCube. These measurements enable determination of the energy spectrum and composition of cosmic rays from PeV to EeV energies, the anisotropy in the distribution of cosmic ray arrival directions, the muon density of cosmic ray air showers, and the PeV gamma-ray flux. Furthermore, IceTop can be used as a veto for the neutrino measurements. The latest results from these IceTop analyses will be presented along with future plans.

Improving the directional reconstruction of PeV hadronic cascades in IceCube

Many neutrino interactions measured by the IceCube Neutrino Observatory produce only hadronic showers, which appear as almost point-like light emission due to the large detector spacing (125 m). At PeV energies these showers often saturate the PMTs closest to the interaction vertex - thus the reconstruction has to rely on more diffused photons which requires precise understanding of the optical properties of the Antarctic ice. Muons produced in the hadronic showers carry information about the neutrino direction, and their Cherenkov light arrives earlier than the photons emitted by the electromagnetic component. A new reconstruction method has been developed which explicitly takes into account the muonic component of hadronic showers and is shown to be robust against systematic ice uncertainties. By applying the new reconstruction, the angular resolution of multi-PeV cascade events can be significantly improved. This will potentially enable follow-up studies of the highest-energy cascade events measured by IceCube.

Dissecting the region around IceCube-170922A: the blazar TXS 0506+056 as the first cosmic neutrino source

On MJD 58018 the IceCube neutrino observatory detected a highlyenergetic, well-reconstructed neutrino, IceCube-170922A, at a distance of 0:1° to a γ-ray flaring blazar, TXS 0506+056. Follow-up searches in archival data additionally revealed a larger flare of neutrinos from the same direction. In order to complete the picture we present here a full multi-wavelength study of the region around IceCube-170922A. While we identify also other non-thermal counterpart candidates, we show that all the evidence points to TXS 0506+056 as the dominant neutrino emitter. Additionally, an analysis of all the available Fermi-LAT data indicates a hard spectrum/low flux of TXS 0506+056 during the neutrino flare in contrast to a soft spectrum/high flux at the arrival time of IceCube-170922A. Putting all the pieces together we conclude that the SED of TXS 0506+056 can be energetically reconnected for both neutrino observations.

Identifying rotation in SASI-dominated core-collapse supernovae with a neutrino gyroscope

Measuring the rotation of core-collapse supernovae (SN) and of their progenitor stars is extremely challenging. Here it is demonstrated that neutrinos may potentially be employed as stellar gyroscopes, if phases of activity by the standing accretion-shock instability (SASI) affect the neutrino emission prior to the onset of the SN explosion. This is shown by comparing the neutrino emission properties of self-consistent, three-dimensional (3D) SN simulations of a 15 M_sun progenitor without rotation as well as slow and fast rotation compatible with observational constraints. The explosion of the fast rotating model gives rise to long-lasting, massive polar accretion downflows with stochastic time-variability, detectable e.g. by the IceCube Neutrino Observatory for any observer direction. While spectrograms of the neutrino event rate of non-rotating SNe feature a well-known sharp peak due to SASI for observers located in the proximity of the SASI plane, the corresponding spectrograms of rotating models show activity over a wide range of frequencies, most notably above 200 Hz for rapid rotation. In addition, the Fourier power spectra of the event rate for rotating models exhibit a SASI peak with lower power than in non-rotating models. The spectra for the rotating models also show secondary peaks at higher frequencies with greater relative heights compared to the main SASI peak than for non-rotating cases. These rotational imprints will be detectable for SNe at 10 kpc or closer.

Compact Star Clusters as Sources of Cosmic Rays and Neutrinos

The origin of cosmic rays is one of the most important questions in modern astrophysics. Leading world observatories are engaged in their search in our Galaxy and beyond. Current observations of bright sources of hard X-rays and gamma radiation require precise models of cosmic-ray accelerators and emission generation. Recent detection of astrophysical neutrinos with the energy exceeding 1015 eV achieved by the IceCube Neutrino Observatory and registration by the LOFAR observatory of the light cosmic-ray component at 1016–1017 eV have given rise to a wide discussion of whether its sources are galactic or extragalactic. H.E.S.S. observations of high-energy gamma-ray sources in compact massive clusters Westerlund 1 and Cl*1806-20 triggered a new search for the models of effective accelerators of high-energy cosmic rays, socalled galactic PeVatrons. In this paper, the properties of compact massive young stellar clusters as possible sources of cosmic rays, neutrinos, and gamma emission are discussed. We suppose that an expanding supernova remnant in a compact massive cluster is an effective cosmic-ray accelerator up to the energies of 1015 eV and beyond. Energy spectra of particles being accelerated in the system of colliding shocks generated by a supernova remnant interaction with nearby stellar winds have a broken power-law shape with a strong upturn around several teraelectronvolts and a cutoff energy at tens of petaelectronvolts. These sources provide the maximal emission flux at the maximal energies of the spectrum. Teraelectronvolt sources detected by H.E.S.S. could be related to supernova remnants in Westerlund 1 and Cl*1806-20 and be responsible for the 10% of the IceCube neutrino events. We have also shown that PeVatrons in the systems of colliding shocks can provide up to 80% of the light cosmic-ray component at the energies of 1016–1017 eV detected at the Earth.

Status and prospects for the IceCube Neutrino Observatory

Abstract The IceCube Neutrino Observatory is located at the geographic South Pole and consists of over 5000 optical sensors embedded in the Antarctic ice along with 81 cosmic ray detector stations on the surface. IceCube was designed to detect high energy neutrinos from extreme astrophysical environments which are potential cosmic ray acceleration sites, such as active galactic nuclei , gamma ray bursts and supernova remnants . The discovery of astrophysical neutrinos by IceCube in 2013 heralded the beginning of neutrino astronomy , and we continue to collect data and explore the properties and potential sources of these neutrinos. An expanded successor called IceCube-Gen2 is in development, with updated optical sensors and calibration devices, and an expanded surface veto. The IceCube-Gen2 detector will search for the sources of cosmic neutrinos and will also include an infill component which will investigate fundamental neutrino physics using atmospheric neutrinos. I will discuss the latest results from IceCube, and the status of IceCube-Gen2.

Very long baseline interferometry radio structure and radio brightening of the high-energy neutrino emitting blazar TXS 0506+056

ABSTRACT We report on the radio brightening of the blazar TXS 0506+056 (at z = 0.3365), and we support its identification by the IceCube Neutrino Observatory as a source of the high-energy (HE) neutrino IC-170922A. Data from the Monitoring Of Jets in AGN with VLBA Experiments (MOJAVE)/Very Long Baseline Array (VLBA) survey indicate that its radio brightness has abruptly increased since 2016 January. When decomposing the total radio flux density curve (in the period 2008 January to 2018 July), provided by the Owens Valley Radio Observatory, into eight Gaussian flares, the peak time of the largest flare overlaps with the HE neutrino detection, while the total flux density has exhibited a threefold increase since 2016 January. We reveal the radio structure of TXS 0506+056 by analysing very long baseline interferometry (VLBI) data from the MOJAVE/VLBA survey. The jet components maintain quasi-stationary core separations. The structure of the ridge line is indicative of a jet curve in the region 0.5–2 mas (2.5–9.9 pc projected) from the VLBI core. The brightness temperature of the core and the pc-scale radio morphology support a helical jet structure at small inclination angle (<8${^{\circ}_{.}}$2). The jet pointing towards the Earth is a key property facilitating multimessenger observations (HE neutrinos, γ-rays and radio flares). The radio brightening preceding the detection of a HE neutrino is similar to the one reported for the blazar PKS 0723–008 and IceCube event ID5.

Modelling the coincident observation of a high-energy neutrino and a bright blazar flare

In September 2017, the IceCube Neutrino Observatory recorded a very-high-energy neutrino in directional coincidence with a blazar in an unusually bright gamma-ray state, TXS0506+056. Blazars are prominent photon sources in the universe because they harbor a relativistic jet whose radiation is strongly collimated and amplified. High-energy atomic nuclei known as cosmic rays can produce neutrinos; thus the recent detection may help identifying the sources of the diffuse neutrino flux and the energetic cosmic rays. Here we report on a self-consistent analysis of the physical relation between the observed neutrino and the blazar, in particular the time evolution and spectral behavior of neutrino and photon emission. We demonstrate that a moderate enhancement in the number of cosmic rays during the flare can yield a very strong increase of the neutrino flux which is limited by co-produced hard X-rays and TeV gamma rays. We also test typical radiation models for compatibility and identify several model classes as incompatible with the observations. We investigate to what degree the findings can be generalized to the entire population of blazars, to determine the relation between their output in photons, neutrinos, and cosmic rays, and suggest how to optimize the strategy of future observations.

Search for neutrinos from decaying dark matter with IceCube

With the observation of high-energy astrophysical neutrinos by the IceCube Neutrino Observatory, interest has risen in models of PeV-mass decaying dark matter particles to explain the observed flux. We present two dedicated experimental analyses to test this hypothesis. One analysis uses 6 years of IceCube data focusing on muon neutrino ‘track’ events from the Northern Hemisphere, while the second analysis uses 2 years of ‘cascade’ events from the full sky. Known background components and the hypothetical flux from unstable dark matter are fitted to the experimental data. Since no significant excess is observed in either analysis, lower limits on the lifetime of dark matter particles are derived: we obtain the strongest constraint to date, excluding lifetimes shorter than 10^{28}hbox { s} at 90% CL for dark matter masses above 10~hbox {TeV}.

Invisible Neutrino Decay Could Resolve IceCube's Track and Cascade Tension.

The IceCube Neutrino Observatory detects high energy astrophysical neutrinos in two event topologies: tracks and cascades. Since the flavor composition of each event topology differs, tracks and cascades can be used to test the neutrino properties and the mechanisms behind the neutrino production in astrophysical sources. Assuming a conventional model for the neutrino production, the IceCube data sets related to the two channels are in >3σ tension with each other. Invisible neutrino decay with lifetime τ/m=10^{2} s/eV solves this tension. Noticeably, it leads to an improvement over the standard nondecay scenario of more than 3σ while remaining consistent with all other multimessenger observations. In addition, our invisible neutrino decay model predicts a reduction of 59% in the number of observed ν_{τ} events which is consistent with the current observational deficit.

After years of listening with detectors buried in Antarctic ice, IceCube researchers trace neutrino source

Almost 4 billion years ago, a brilliantly bright galaxy fired a burst of lightweight, fast-moving particles toward Earth (1). Now, an observatory at the South Pole has traced those particles back to their source, potentially solving a century-old mystery about the waves of radiation produced somewhere outside the solar system that wash over our planet each day. But researchers will have to continue to examine the proposed source in multiple wavelengths to ensure they’ve identified the culprit. Researchers at the IceCube Neutrino Observatory, launched in 2002, have for the first time been able to trace some of the most energetic neutrinos back to their purported source, the blazar TXS 0506+056. Image courtesy of National Science Foundation/IceCube. Neutrinos are born from some of the most violent events in the universe, including explosive supernovae and the chaotic environment around supermassive black holes. Tracing neutrinos back to their source can help scientists better understand these destructive events. Deep in the ice of Antarctica, the IceCube Neutrino Observatory, launched in 2002, hunts for neutrinos, subatomic particles so weak that they usually pass through normal matter undetected (see www.pnas.org/content/111/24/8699). Every second, roughly 100 billion neutrinos pass through 1 square centimeter on Earth, flying at nearly the speed of light. Many of them come from the sun. But the more powerful neutrinos are created outside of the galaxy, generated by a process researchers have only speculated about. For the first time, researchers have been able to trace some of the most energetic particles back to their source, the blazar TXS 0506+056. One of the top suspects in the formation of neutrinos, blazars are a class of active galaxy nuclei (AGNs) that form from a supermassive black hole. Although the black hole devours most of the material around it, some of the gas and dust is deflected …