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The energy density of cosmic neutrinos measured by IceCube matches the one observed by Fermi in extragalactic photons that predominantly originate in blazars. This has inspired attempts to match Fermi sources with IceCube neutrinos. A spatial association combined with a coincidence in time with a flaring source may represent a smoking gun for the origin of the IceCube flux. In June 2015, the Fermi Large Area Telescope observed an intense flare from blazar 3C 279 that exceeded the steady flux of the source by a factor of forty for the duration of a day. We show that IceCube is likely to observe neutrinos, if indeed hadronic in origin, in data that are still blinded at this time. We also discuss other opportunities for coincident observations that include a recent flare from blazar 1ES 1959+650 that previously produced an intriguing coincidence with AMANDA observations.
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Motivated by the observation of a $>290$ TeV muon neutrino by IceCube, coincident with a $sim$6 month-long $gamma$-ray flare of the blazar TXS 0506+056, and an archival search which revealed $13 pm 5$ further, lower-energy neutrinos in the direction of the source in 2014-2015, we discuss the likely contribution of blazars to the diffuse high-energy neutrino intensity, the implications for neutrino emission from TXS 0506+056 based on multi-wavelength observations of the source, and a multi-zone model that allows for sufficient neutrino emission so as to reconcile the multi-wavelength cascade constraints with the neutrino emission seen by IceCube in the direction of TXS 0506+056.
Motivated by the recently reported evidence of an association between a high-energy neutrino and a gamma-ray flare from the blazar TXS 0506+056, we calculate the expected high-energy neutrino signal from past, individual flares, from twelve blazars, selected in declinations favourable for detection with IceCube. To keep the number of free parameters to a minimum, we mainly focus on BL Lac objects and assume the synchrotron self-Compton mechanism produces the bulk of the high-energy emission. We consider a broad range of the allowed parameter space for the efficiency of proton acceleration, the proton content of BL Lac jets, and the presence of external photon fields. To model the expected neutrino fluence we use simultaneous multi-wavelength observations. We find that in the absence of external photon fields and with jet proton luminosity normalised to match the observed production rate of ultra-high-energy cosmic rays, individual flaring sources produce a modest neutrino flux in IceCube, $lesssim10^{-3}$ muon neutrinos with energy exceeding 100 TeV, stacking ten years of flare periods selected in the >800 MeV Fermi energy range from each source. Under optimistic assumptions about the jet proton luminosity and in the presence of external photon fields, we find that the two most powerful sources in our sample, AO 0235+164, and OJ 287, would produce, in total, $approx 3$ muon neutrinos during ten years of Fermi flaring periods, in future neutrino detectors with total instrumented volume $sim$ten times larger than IceCube,or otherwise, constrain the proton luminosity of blazar jets.
The standard perception is that the detection of high energy (TeV energies and above) neutrinos from an astrophysical object is a conclusive evidence for the presence of hadronic cosmic rays at the source. In the present work we demonstrate that TeV neutrinos can also be originated from energetic electrons via electromagnetic interactions in different potential cosmic ray sources with flux levels comparable to that of the hadronic originated neutrinos at high energies. Our findings thus imply that at least a part of the neutrinos observed by Icecube observatory may be originated from energetic electrons. The present analysis further suggests that only a combine study of TeV gamma rays and neutrinos over a wide energy range from an astrophysical object can unambiguously identify the nature of their parents, hadrons or leptons.
Neutrinos offer a window to physics beyond the Standard Model. In particular, high-energy astrophysical neutrinos, with TeV-PeV energies, may provide evidence of new, secret neutrino-neutrino interactions that are stronger than ordinary weak interactions. During their propagation over cosmological distances, high-energy neutrinos could interact with the cosmic neutrino background via secret interactions, developing characteristic energy-dependent features in their observed energy distribution. For the first time, we look for signatures of secret neutrino interactions in the diffuse flux of high-energy astrophysical neutrinos, using 6 years of publicly available IceCube High Energy Starting Events (HESE). We find no significant evidence for secret neutrino interactions, but place competitive upper limits on the coupling strength of the new mediator through which they occur, in the mediator mass range of 1-100 MeV.
High-energy neutrinos from decays of mesons, produced in collisions of cosmic ray particles with air nuclei, form unavoidable background for detection of astrophysical neutrinos. More precise calculations of the high-energy neutrino spectrum are required since measurements in the IceCube experiment reach the intriguing energy region where a contribution of the prompt neutrinos and/or astrophysical ones should be discovered. Basing on the referent hadronic models QGSJET II-03, SIBYLL 2.1, we calculate high-energy spectra, both of the muon and electron atmospheric neutrinos, averaged over zenith-angles. The computation is made using three parameterizations of cosmic ray spectra which include the knee region. All calculations are compared with the atmospheric neutrino measurements by Frejus and IceCube. The prompt neutrino flux predictions obtained with thequark-gluon string model (QGSM) for the charm production by Kaidalov & Piskunova do not contradict to the IceCube measurements and upper limit on the astrophysical muon neutrino flux. Neutrino flavor ratio, $phi_{ u_ mu}/phi_{ u_e}$, extracted from IceCube data decreases in the energy range $0.1 - 5$ TeV energy contrary to that one might expect from the conventional neutrino flux. Presumable reasons of such behavior are: i) early arising contribution from decays of charmed particle, differing from predictions of present models, ii) revealed diffuse flux of astrophysical electron neutrinos. The likely diffuse flux of astrophysical neutrinos related to the PeV neutrino events, detected in the IceCube experiment, leads to a decrease of the flavor ratio at the energy below 10 TeV, that is in qualitative agreement with a rough approximation for theflavor ratio obtained from the IceCube data.
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