Cosmic ray accelerators like supernova and hypernova remnants in star forming galaxies are one of the most plausible sources of the IceCube observed diffuse astrophysical neutrinos. The neutrino producing hadronic processes will also produce a diffuse gamma ray flux, constrained by the Fermi-LAT bounds. The fact that point sources like blazars also contribute to the diffuse gamma ray flux implies large gamma opacity of the neutrino sources. Indeed, for these high redshift star forming galaxies the gamma absorption during the intergalactic propagation can be significant. In addition, large gamma attenuation inside these extreme source galaxies can reduce the cascade component of the diffuse flux. Under the current astrophysical uncertainties affecting these absorptions processes, we find the associated diffuse gamma ray flux can remain compatible with the current Fermi-LAT bounds.
IceCube has detected many TeV--PeV neutrinos, but their astrophysical origins remain largely unknown. Motivated by the observed late-time X-ray/optical bumps in some gamma-ray bursts (GRBs), we examine the correlation between IceCube neutrinos and GRBs allowing delayed neutrinos $\sim$days after the prompt gamma rays. Although we have not found any definitive correlation, up to $\sim$10\% of the events observed so far at IceCube may have been neutrinos produced by the late-time GRB activities at $\sim$1 day. Assuming a connection between some IceCube events and the late GRB bumps, we show in a…
A signal of high-energy extraterrestrial neutrinos from unknown source(s) was recently discovered by the IceCube experiment. Neutrinos are always produced together with gamma-rays, but the gamma-ray flux from extragalactic sources is suppressed due to attenuation in the intergalactic medium. We report the discovery of a gamma-ray excess at high Galactic latitudes starting at energies 300 GeV in the data of the Fermi telescope. We show that the multi-TeV gamma-ray diffuse emission has spectral characteristics at both low and high Galactic latitudes compatible with those of the IceCube high neut…
We compute the gamma-ray and neutrino diffuse emission of the Galaxy on the basis of a recently proposed phenomenological model characterized by radially dependent cosmic-ray (CR) transport properties. We show how this model, designed to reproduce both Fermi-LAT gamma-ray data and local CR observables, naturally reproduces the anomalous TeV diffuse emission observed by Milagro in the inner Galactic plane. Above 100 TeV our picture predicts a neutrino flux that is about five (two) times larger than the neutrino flux computed with conventional models in the Galactic Center region (full-sky). Exp…
The IceCube Collaboration is currently building the world's largest neutrino telescope at the South Pole to observe high energy neutrinos from a variety of astrophysical sources. In this paper we review the current status of the IceCube experiment, highlighting some of the results obtained so far.
We show that the Galactic latitude distribution of IceCube astrophysical neutrino events with energies above 100~TeV is inconsistent with the isotropic model of the astrophysical neutrino flux. Namely, the Galactic latitude distribution of the events shows an excess at low latitudes |b|<10 degrees and a deficit at high Galactic latitude |b|> 50 degrees. We use Monte-Carlo simulations to show that the inconsistency of the isotropic signal model with the data is at > 3 sigma level, after the account of trial factors related to the choice of the low-energy threshold and Galactic latitude binning …
The IceCube Collaboration has observed 37 neutrino events in the energy range $30\, TeV\leq E_ν \leq 2$ PeV and the sources of these neutrinos are unknown. Here we have shown that positions of 12 high energy blazars and the position of the FR-I galaxy Centaurus A, coincide within the error circles of ten IceCube events, the later being in the error circle of the highest energy event so far observed by IceCube. Two of the above blazars are simultaneously within the error circles of the Telescope Array hotspot and one IceCube event. We found that the blazar H2356-309 is within the error circles …
We use 10 years of publicly available IceCube data to investigate the correlations between high-energy neutrinos and various Fermi-LAT gamma-ray samples. This work considers the following gamma-ray samples: the third Fermi-LAT catalog of high-energy sources(3FHL), >100GeV Fermi-LAT events, LAT 12-year source catalog(4FGL), the fourth catalog of active galactic nuclei(4LAC) and subsets of these samples. For each sample, both a single-source analysis and a stacking analysis are performed. We find no indication that the sources in these samples produce significant high-energy neutrinos. From the …
The recent discovery of a diffuse neutrino flux up to PeV energies raises the question of which populations of astrophysical sources contribute to this diffuse signal. One extragalactic candidate source population to produce high-energy neutrinos are Blazars. We present results from a likelihood analysis searching for cumulative neutrino emission from Blazar populations selected with the 2nd Fermi-LAT AGN catalog (2LAC) using an IceCube data set that has been optimized for the detection of individual sources. In contrast to previous searches with IceCube, the investigated populations contain u…
Starburst galaxies, which are known as "reservoirs" of high-energy cosmic-rays, can represent an important high-energy neutrino "factory" contributing to the diffuse neutrino flux observed by IceCube. In this paper, we revisit the constraints affecting the neutrino and gamma-ray hadronuclear emissions from this class of astrophysical objects. In particular, we go beyond the standard prototype-based approach leading to a simple power-law neutrino flux, and investigate a more realistic model based on a data-driven blending of spectral indexes, thereby capturing the observed changes in the proper…
Late time decay of very heavy dark matter is considered as one of the possible explanations for diffuse PeV neutrinos observed in IceCube. We consider implications of multimessenger constraints, and show that proposed models are marginally consistent with the diffuse gamma-ray background data. Critical tests are possible by a detailed analysis and identification of the sub-TeV isotropic diffuse gamma-ray data observed by Fermi and future observations of sub-PeV gamma rays by observatories like HAWC or Tibet AS+MD. In addition, with several-year observations by next-generation telescopes such a…
Superheavy dark matter may show its presence in high energy neutrino signals detected on earth. From the latest results of IceCube, we could set the strongest lower bound on the lifetime of dark matter beyond 100 TeV around $10^{28} {\rm sec}$. The excess around a PeV is noticed and may be interpreted as the first signal of DM even though further confirmation and dedicated searches are invited.
High energy neutrino astrophysics has come of age with the discovery by IceCube of neutrinos in the TeV to PeV energy range attributable to extragalactic sources at cosmological distances. At such energies, astrophysical neutrinos must have their origin in cosmic ray interactions, providing information about the sources of high energy cosmic rays, as well as leading to the co-production of high energy gamma-rays. The intimate link with these latter two independently observed types of radiation provides important tools in the search for identifying and understanding the nature of their astrophy…
We present results of an archival coincidence analysis between Fermi LAT gamma-ray data and public neutrino data from the IceCube neutrino observatory's 40-string (IC40) and 59-string (IC59) observing runs. Our analysis has the potential to detect either a statistical excess of neutrino + gamma-ray ($ν$+$γ$) emitting transients or, alternatively, individual high gamma-multiplicity events, as might be produced by a neutrino observed by IceCube coinciding with a LAT-detected gamma-ray burst. Dividing the neutrino data into three datasets by hemisphere (IC40, IC59-North, and IC59-South), we const…
Despite the spectacular discovery of an astrophysical neutrino flux by IceCube in 2013, its origin remains a mystery. Whatever its sources, we expect the neutrino flux to be accompanied by a comparable gamma-ray flux. These photons should be degraded in energy by electromagnetic cascades and contribute to the diffuse GeV-TeV flux precisely measured by the Fermi-LAT. Population studies have also permitted to identify the main classes of contributors to this flux, which at the same time have not been associated with major neutrino sources in cross-correlation studies. These considerations allow …
Cosmological parameters deduced from the Planck measurements of anisotropies in the cosmic microwave background are at some tension with direct astronomical measurements of various parameters at low redshifts. Very recently, it has been conjectured that this discrepancy can be reconciled if a certain fraction of dark matter is unstable and decays between recombination and the present epoch. Herein we show that if the superheavy relics have a branching into neutrinos B (X \to ν\bar ν) \sim 3 \times 10^{-9}, then this scenario can also accommodate the recently discovered extraterrestrial flux of…
The recent high-statistics high-energy atmospheric neutrino data collected by IceCube open a new window to probe new physics scenarios that are suppressed in lower energy neutrino experiments. In this paper we analyze the IceCube atmospheric neutrino data to constrain the Violation of Equivalence Principle (VEP) in the framework of three neutrinos with non-universal gravitational couplings. In this scenario the effect of VEP on neutrino oscillation probabilities can be parametrized by two parameters $Δγ_{21}\equiv γ_2-γ_1$ and $Δγ_{31}\equiv γ_3-γ_1$, where $γ_i$'s denote the coupling of neutr…
The center of the Milkyway is a host to energetic phenomena across many electromagnetic wave-bands and now possibly of high-energy neutrinos. We show that 5 out of 21 IceCube shower-like events, including a PeV event, likely originated from the Galactic Center region. Hard spectrum and flux inferred from these events are inconsistent with atmospheric neutrinos. The flux of these neutrinos is consistent with an extrapolation of the gamma-ray flux measured by Fermi-LAT from the inner Galactic region. This indicates a common hadronic origin of both, powered by supernovae. Three other shower-like …
The 6-year dataset of high-energy starting events (HESE) at IceCube indicates a spectrum of astrophysical neutrinos much softer than expected from the Fermi shock acceleration mechanism. On the other hand, IceCube's up-going muon neutrino dataset and Fermi-LAT's gamma-ray spectrum point to an $E^{-2}$ neutrino spectrum. If the HESE data above 200 TeV are fit with the latter flux, an excess at lower energies ensues, which then suggests a multicomponent spectrum. We show that the HESE dataset can be explained by a single $E^{-2}$ power-law neutrino flux from a muon-damped $pγ$ source if neutrino…
The IceCube (IC) collaboration recently reported the detection of TeV-PeV extraterrestrial neutrinos whose origin is yet unknown. By the photon-neutrino connection in $pp$ and $pγ$ interactions, we use the \fermi-LAT observations to constrain the origin of the IC detected neutrinos. We find that Galactic origins, i.e., the diffuse Galactic neutrinos due to cosmic ray (CR) propagation in the Milky Way, and the neutrinos from the Galactic point sources, may not produce the IC neutrino flux, thus these neutrinos should be of extragalactic origin. Moreover, the extragalactic gamma-ray bursts (GRBs…
IceCube, a cubic-kilometer sized neutrino detector at the Geographic South Pole, has recently discovered a diffuse all-flavor flux of astrophysical neutrinos. However, the corresponding astrophysical sources have not yet been identified in current IceCube analyses. We present a method to interpret the results of a recently published angular correlation analysis in IceCube searching for spatial clustering of muon neutrino events in terms of astrophysical models (given by an arbitrary source count distribution). We exemplarily show the resulting limits on the parameters of a class of source coun…
Muons with a high transverse momentum (p_T) are produced in cosmic ray air showers via semileptonic decay of heavy quarks and the decay of high p_T kaons and pions. These high p_T muons have a large lateral separation from the shower core muon bundle. IceCube is well suited for the detection of high p_T muons. The surface shower array can determine the energy, core location and direction of the cosmic ray air shower while the in-ice array can reconstruct the energy and direction of the high p_T muon. This makes it possible to measure the decoherence function (lateral separation spectrum) at di…
The first ever identification of a cosmic ray accelerator as the consequence of spacial and temporal correlation of IceCube event 170922A with flaring of a blazar TXS 0506+056 motivated us to look for other flaring blazars in Fermi-LAT 3FGL catalog, which could be correlated with IceCube high energy track events. We have studied the Fermi-LAT light curves of blazars correlated with neutrino track events. Among the eight sources identified within 2$σ$ angular uncertainty of the IceCube track events selected in our study, we find only one source 3FGL J2255+2409 was in flaring state during the ne…
IceCube has reported the detection of a diffuse TeV-PeV neutrino emission, for which the flat spectrum radio quasars (FSRQs) have been proposed to be the candidate sources. Here we assume that the neutrino flux from FSRQs is proportional to their gamma-ray ones, and obtain the gamma-ray/neutrino flux ratio by the diffuse gamma-ray flux from Fermi-LAT measurement of FSRQs and the diffuse neutrino flux detected by IceCube. We apply this ratio to individual FSRQs and hence predict their neutrino flux. We find that a large fraction of candidate FSRQs from the northern sky in the IceCube point sour…
Instrumenting a gigaton of ice at the geographic South Pole, the IceCube Neutrino Observatory has been at the forefront of groundbreaking scientific discoveries over the past decade. These include the observation of a flux of TeV-PeV astrophysical neutrinos, detection of the first astrophysical neutrino on the Glashow resonance and evidence of the blazar TXS 0506+056 as the first known astronomical source of high-energy neutrinos. Several questions, however, remain, pertaining to the precise origins of astrophysical neutrinos, their production mechanisms at the source and in Earth's atmosphere…
We analyze the energy and zenith angle distributions of the latest 2-year IceCube dataset of upward going atmospheric neutrinos to constrain sterile neutrinos at the eV scale in the 3+1 scenario. We find that the parameters favored by a combination of LSND and MiniBooNE data are excluded at more than the 99% C.L. We explore the impact of nonstandard matter interactions on this exclusion, and find that the exclusion holds for nonstandard interactions (NSI) that are within the stringent model-dependent bounds set by collider and neutrino scattering experiments. However, for large NSI parameters …
IceCube is the first representative of the km^3 class of neutrino telescopes and currently the most sensitive detector to high-energy neutrinos. Its main mission is to search for Galactic and extragalactic sources of high-energy neutrinos, but it is also an excellent detector for the investigation of a variety of other highly topical astrophysics and particle physics topics like supernovae, dark matter and neutrino oscillations. After an introduction to neutrino astronomy and neutrino telescopes, this article presents a selection of latest results from the IceCube neutrino detector with respec…
The IceCube Collaboration has published four years of data and the observed neutrino flux is significantly in excess of the expected atmospheric background. Due to the steeply falling atmospheric background spectrum, events at the highest energies are most likely extraterrestrial. In our previous approach we have studied blazars as the possible origin of the High-Energy Starting Events (HESE) neutrino events at PeV energies. In this work we extend our study to include all HESE neutrinos (which does not include IC 170922A) at or above a reconstructed energy of 100 TeV, but below 1 PeV. We study…
Dozens of high-energy neutrinos have been detected by the IceCube neutrino telescope, but no clear association with any classes of astrophysical sources has been identified so far. Recently, Kadler et al. (2016) report that a PeV cascade-like neutrino event occurs in positional and temporal coincidence with a giant gamma-ray flare of the blazar PKS B1424-418. Since IceCube track-like events have much better angular resolution, we here search for possible short-term gamma-ray flares that are associated with the IceCube track-like events with Fermi Large Area Telescope (LAT) observations. Among …
The Zwicky Transient Facility (ZTF) follow-up campaign of alerts released by the IceCube Neutrino Observatory has led to the likely identification of the transient AT2019fdr as the source of the neutrino event IC200530A. AT2019fdr was initially suggested to be a tidal disruption event in a Narrow-Line Seyfert 1 galaxy. However, the combination of its spectral properties, color evolution, and feature-rich light curve suggests that AT2019fdr may be a Type IIn superluminous supernova. In the latter scenario, IC200530A may have been produced via inelastic proton-proton collisions between the relat…
The IceCube Neutrino Observatory is the world's largest neutrino detector, instrumenting a cubic kilometer of ice at the geographic South Pole. The detector probes neutrino energies from GeV to PeV, and collects high statistics neutrino samples by virtue of its extremely large volume. IceCube was designed to detect high-energy neutrinos from potential cosmic ray acceleration sites such as active galactic nuclei, gamma ray bursts and supernova remnants. IceCube announced the detection of a diffuse flux of astrophysical neutrinos in 2013, including the highest energy neutrinos ever detected. Ice…
In this review I discuss the ultra-high energy neutrinos (UHEN) originated from Cosmic-Rays propogation (GZK neutrinos) and from Gamma Ray Bursts (GRBs), and discuss their detectability in kilometers scale detectors like ARA and IceCube. While GZK neutrinos are expected from cosmic ray interactions on the CMB, the GRB neutrinos depend on the physics inside the sources. GRBs are predicted to emit UHEN in the prompt and in the later 'after-glow' phase. I discuss the constraints on the hadronic component of GRBs derived from the search of four years of IceCube data for a prompt neutrino fux from …
Multi-messenger searches for gravitational waves and high-energy neutrinos provide important insights into the dynamics of and particle acceleration by black holes and neutron stars. With LIGO's third observing period (O3), the number of gravitational wave detections has been substantially increased. The rapid identification of joint signals is crucial for electromagnetic follow-up observations of transient emission that is only detectable for short periods of time. High-energy neutrino direction can be reconstructed to sub-degree precision, making a joint detection far better localized than a…
The IceCube Neutrino Observatory, which instruments 1$\,$km$^3$ of clear ice at the geographic South Pole, was mainly designed to detect particles with energies in the multi-GeV to PeV range. Due to ice temperatures between $-20^\circ$C to $-43^\circ$C and the low radioactivity of the ice, the dark noise rates of the 5160 photomultiplier tubes forming the IceCube lattice are of order 500 Hz, which is particularly low for 10 inch photomultipliers. Therefore, IceCube can extend its searches to bursts of $\mathcal{O}$(10$\,$MeV) neutrinos lasting several seconds, which are expected to be produced…
We perform a combined likelihood analysis for the IceCube 6-year high-energy starting events (HESE) and 8-year throughgoing muon events above 10 TeV using a two-component neutrino flux model. The two-component flux can be motivated either from purely astrophysical sources or due to a beyond Standard Model contribution, such as decaying heavy dark matter. We find that the astrophysical plus dark matter interpretation is mildly preferred by the current data over the purely astrophysical explanation. As for the astrophysical neutrinos, we consider two different source flavor compositions correspo…
We have determined the currently allowed regions of the parameter spaces of two representative models of diffuse neutrino flux from active galactic nuclei (AGN): one by Koers & Tinyakov (KT) and another by Becker & Biermann (BB). Our observable has been the number of upgoing muon-neutrinos expected in the 86-string IceCube detector, after 5 years of exposure, in the range 10^5 < E/GeV < 10^8. We have used the latest estimated discovery potential of the IceCube-86 array at the 5-sigma level to determine the lower boundary of the regions, while for the upper boundary we have used either the AMAN…
IceCube is a cubic-kilometer Cherenkov detector located in the deep ice at the geographic South Pole. The dominant event yield in the deep ice detector consists of penetrating atmospheric muons produced in cosmic ray air showers with energies above several 100 GeV. In addition, the surface array, IceTop, deployed above the IceCube deep ice detector, measures the electromagnetic signal and low-energy muons of the air shower. Hence, IceCube and IceTop yield unique opportunities to study cosmic rays with large statistics in great detail. We discuss the latest results of air shower measurements fr…
Located at the South Pole, the IceCube Neutrino Observatory is the world largest neutrino telescope, instrumenting one cubic kilometre of Antarctic ice at a depth between 1450m to 2450m. In 2013 IceCube reported the first observations of a diffuse astrophysical high-energy neutrino flux. Although the IceCube Collaboration has identified more than 100 high-energy neutrino events, the origin of this neutrino flux is still not known. Blazars, a subclass of Active Galactic Nuclei and one of the most powerful classes of objects in the Universe, have long been considered promising sources of high en…
Realtime analyses are necessary to identify the source of high energy neutrinos. As an observatory with a 4$π$ steradian field of view and near-100% duty cycle, the IceCube Neutrino Observatory is a unique facility for investigating transients. In 2016, IceCube established a pipeline that uses low-latency data to rapidly respond to astrophysical events that were of interest to the multi-messenger observational community. Here, we describe this pipeline and summarize the results from all of the analyses performed since 2016. We focus not only on those analyses which were performed in response t…
A radio-emitting tidal disruption event (AT2019dsg) is proposed as a likely counterpart of the IceCube neutrino event IC-191001A. In this work we have revisited the {\it Fermi}-LAT data in the direction of the neutrino and confirmed no signal at the site of AT2019dsg. Instead, at the edge of the 90\% confidential level error region of this neutrino there is a $γ$-ray transient source associated with a blazar GB6 J2113+1121. In May 2019, GB6 J2113+1121 was undergoing an unprecedented $γ$-ray flare since the start of the {\it Fermi}-LAT operation, with a variability amplitude about 20-fold. Simi…
The origin of neutrino flux observed in IceCube is still mainly unknown. Typically two flux components are assumed, namely: atmospheric neutrinos and an unknown astrophysical term. In principle the latter could also contain a top-down contribution coming for example from decaying dark matter. In this case one should also expect prompt and secondary gammas as well. This leads to the possibility of a multimessenger analysis based on the simultaneous comparison of the Dark Matter hypothesis both with neutrino and high energy gamma rays data. In this paper, we analyze, for different decaying Dark …
It has been speculated that Lorentz-invariance violation (LIV) might be generated by quantum-gravity (QG) effects. As a consequence, particles may not travel at the universal speed of light. In particular, superluminal extragalactic neutrinos would rapidly lose energy via the bremssthralung of electron-positron pairs (nu -> nu e+ e-), damping their initial energy into electromagnetic cascades, a figure constrained by Fermi-LAT data. We show that the two cascade neutrino events with energies around 1 PeV recently detected by IceCube -if attributed to extragalactic diffuse events, as it appears …
Since the discovery of a neutrino flux in excess of the atmospheric background by the IceCube Collaboration, searches for the astrophysical sources have been ongoing. Due to the steeply falling background towards higher energies, the PeV events detected in three years of IceCube data are the most likely ones to be of extraterrestrial origin. Even excluding the PeV events detected so far, the neutrino flux is well above the atmospheric background, so it is likely that a number of sub-PeV events originate from the same astrophysical sources that produce the PeV events. We study the high-energy p…
The IceCube Neutrino Observatory has discovered a diffuse all-flavor flux of high-energy astrophysical neutrinos. However, the corresponding astrophysical sources have not yet been identified. Neither significant point sources nor significant angular correlations of event directions have been observed by IceCube or other instruments to date. We present a new method to interpret the non-observation of angular correlations in terms of exclusions on the strength and number of point-like sources in generic astrophysical scenarios. Additionally, we constrain the presence of these sources taking int…
Construction of the cubic-kilometer neutrino detector IceCube at the South Pole has been completed in December 2010. It forms a lattice of 5160 photomultiplier tubes monitoring a gigaton of the deep Antarctic ice for particle induced photons. The telescope is primarily designed to detect neutrinos with energies greater than 100 GeV from astrophysical sources. Beyond this astrophysical motivation IceCube is also a discovery instrument for the search for physics beyond the Standard Model. Owing to subfreezing ice temperatures, the photomultiplier dark noise rates are particularly low which opens…
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 …
The origin of astrophysical high-energy neutrinos detected by the IceCube Neutrino Observatory remains a mystery to be solved. In this paper we search for neutrino source candidates within the $90$% containment area of $70$ track-type neutrino events recorded by the IceCube Neutrino Observatory. By employing the Fermi-LAT 4FGL-DR2, the Swift-XRT 2SXPS and the CRATES catalogs, we identify possible gamma, X-ray and flat-spectrum radio candidate sources of track-type neutrinos. We find that based on the brightness of sources and their spatial correlation with the track-type IceCube neutrinos, the…
The sources of IceCube neutrinos are as yet unknown. The multi-messenger observation of their emission in $γ$-rays can be a guide to their identification, as exemplified by the case of TXS 0506+056. We suggest a new method of searching for $γ$-rays with Imaging Air Cherenkov Telescopes from sources in coincidence with possible astrophysical neutrinos. We propose that searches of $γ$-rays are extended, from the current practice of only a few days, to up to one month from a neutrino alert. We test this strategy on simulated sources modeled after the blazar \emph{TXS 0506+056-like}, emitting neut…
In this work we use a multi-messenger approach to determine if the high energy diffuse neutrino flux observed by the IceCube Observatory can originate from $γ$-ray sources powered by Cosmic Rays interactions with gas. Typical representatives of such sources are Starburst and Ultra-Luminous Infrared Galaxies. Using the three most recent calculations of the non-blazar contribution to the extragalactic $γ$-ray background measured by the Fermi-LAT collaboration, we find that a hard power-law spectrum with spectral index $α\leq 2.12$ is compatible with all the estimations for the allowed contributi…
