Astrophysical neutrinos could originate from blazars, but their modelling is challenging. Instead, the source of cosmic neutrinos could be a special yet unidentified class in which jets burrow ...through stellar material and produce neutrinos.
Abstract
The diffuse flux of cosmic neutrinos has been measured by the IceCube Observatory from TeV to PeV energies. We show that an improved characterization of this flux at lower energies, TeV and ...sub-TeV, reveals important information on the nature of the astrophysical neutrino sources in a model-independent way. Most significantly, it could confirm the present indications that neutrinos originate in cosmic environments that are optically thick to GeV–TeV
γ
-rays. This conclusion will become inevitable if an uninterrupted or even steeper neutrino power law is observed in the TeV region. In such
γ
-ray-obscured sources, the
γ
-rays that inevitably accompany cosmic neutrinos will cascade down to MeV–GeV energies. The requirement that the cascaded
γ
-ray flux accompanying cosmic neutrinos should not exceed the observed diffuse
γ
-ray background puts constraints on the peak energy and density of the radiation fields in the sources. Our calculations inspired by the existing data suggest that a fraction of the observed diffuse MeV–GeV
γ
-ray background may be contributed by neutrino sources with intense radiation fields that obscure the high-energy
γ
-ray emission accompanying the neutrinos.
A multimessenger campaign has associated a high-energy cosmic neutrino with a distant gamma-ray blazar, TXS 0506+056. IceCube archival data subsequently revealed that the high-energy neutrino flux ...from the direction of this source, integrated over the last 10 yr, is dominated by a single bright neutrino flare in 2014, leaving the multimessenger flare as a subluminous second flare. The extraordinary brightness of the blazar despite its distance suggests that it may belong to a special class of sources that produce cosmic rays. We show that the diffuse IceCube flux discovered in 2013 can be accommodated by a subclass of blazars, on the order of 5%, that episodically produce neutrinos with the luminosity of the 2014 neutrino flare. Matching the cosmic-ray flux required to produce the neutrinos to the one observed implies highly efficient neutrino sources with large target photon densities that are not transparent to high-energy gamma-rays. The opacity of the source modifies the straightforward multimessenger connection in a way that is consistent with the gamma-ray observations coincident with the 2014 neutrino flare.
The chargeless, weakly interacting neutrinos are ideal astronomical messengers as they travel through space without scattering, absorption or deflection. But this weak interaction also makes them ...notoriously difficult to detect, leading to neutrino observatories requiring large-scale detectors. A few years ago, the IceCube experiment discovered neutrinos originating beyond the Sun with energies bracketed by those of the highest energy gamma rays and cosmic rays. I discuss how these high-energy neutrinos can be detected and what they can tell us about the origins of cosmic rays and about dark matter.
IceCube Gaisser, Thomas; Halzen, Francis
Annual review of nuclear and particle science,
10/2014, Volume:
64, Issue:
1
Journal Article
Peer reviewed
Open access
IceCube is the first kilometer-scale neutrino detector. Built primarily for neutrino astronomy, it has recently discovered events with energies above 100 TeV that are likely to be from distant ...sources beyond the solar system. Among the events are three with deposited energies of more than 1 PeV, the highest-energy neutrinos ever detected. We review the astrophysical arguments that motivate such a large detector, and we describe how it works and how the high-energy events are reconstructed and identified above the background of atmospheric neutrinos. We also describe the broad range of neutrino physics and particle astrophysics topics addressed by IceCube, as well as its potential for the future.
Abstract
High-energy neutrinos are detected by the IceCube Observatory in the direction of NGC 1068, the archetypical type II Seyfert galaxy. The neutrino flux, surprisingly, is more than an order of ...magnitude higher than the
γ
-ray upper limits at measured TeV energy, posing tight constraints on the physical conditions of a neutrino production site. We report an analysis of the submillimeter, mid-infrared, and ultraviolet observations of the central 50 pc of NGC 1068 and suggest that the inner dusty torus and the region where the jet interacts with the surrounding interstellar medium (ISM) may be a potential neutrino production site. Based on radiation and magnetic field properties derived from observations, we calculate the electromagnetic cascade of the
γ
-rays accompanying the neutrinos. When injecting protons with a hard spectrum, our model may explain the observed neutrino flux above ∼10 TeV. It predicts a unique sub-TeV
γ
-ray component, which could be identified by a future observation. Jet–ISM interactions are commonly observed in the proximity of jets of both supermassive and stellar-mass black holes. Our results imply that such interaction regions could be
γ
-ray-obscured neutrino production sites, which are needed to explain the IceCube diffuse neutrino flux.
Abstract
Despite the uncovered association of a high-energy neutrino with the apparent flaring state of blazar TXS 0506+056 in 2017, the mechanisms leading to astrophysical particle acceleration and ...neutrino production are still uncertain. Recent studies found that when transparent to
γ
-rays,
γ
-flaring blazars do not have the opacity for protons to produce neutrinos. Here we present observational evidence for an alternative explanation, in which
γ
-ray emission is suppressed during efficient neutrino production. A large proton and target photon density helps produce neutrinos while temporarily suppressing the observable
γ
-emission due to a large
γ
γ
opacity. We show that the Fermi-LAT
γ
-flux of blazar PKS 1502+106 was at a local minimum when IceCube recorded the coincident high-energy neutrino IC-190730A. Using data from the OVRO 40 m Telescope, we find that radio emission from PKS 1502+106 at the time period of the coincident neutrino IC-190730A was in a high state, in contrast to earlier time periods when radio and
γ
fluxes are correlated for both low and high states. This points to an active outflow that is
γ
-suppressed at the time of neutrino production. We find similar local
γ
-suppression in other blazars, including in MAGIC’s TeV flux of TXS 0506+056 and Fermi-LAT’s flux of blazar PKS B1424-418 at the time of coincident IceCube neutrino detections. Using temporary
γ
-suppression, neutrino–blazar coincidence searches could be substantially more sensitive than previously assumed, enabling the identification of the origin of IceCube’s diffuse neutrino flux possibly with already existing data.
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