Association of IceCube neutrinos with radio sources observed at Owens Valley and Metsähovi Radio Observatories

Abstract

Context. Identifying the most likely sources for high-energy neutrino emission has been one of the main topics in high-energy astrophysics ever since the first observation of high-energy neutrinos by the IceCube Neutrino Observatory. Active galactic nuclei with relativistic jets, blazars, have been considered to be one of the main candidates due to their ability to accelerate particles to high energies.Aims. We study the connection between radio emission and IceCube neutrino events using data from the Owens Valley Radio Observatory and Metsähovi Radio Observatory blazar monitoring programs. Methods. We identify sources in our radio monitoring sample, which are positionally consistent with IceCube high-energy neutrino events. We estimate their mean flux density and variability amplitudes around the neutrino arrival time, and compare these with values from random samples to establish the significance of our results. Results. We find radio source associations within our samples with 16 high-energy neutrino events detected by IceCube. Nearly half of the associated sources are not detected in the γ-ray energies, but their radio variability properties and Doppler boosting factors are similar to the γ-ray detected objects in our sample so that they could still be potential neutrino emitters. We find that the number of strongly flaring objects in our samples is unlikely to occur due to a random coincidence (at 2σ level), and in the case of OVRO samples, the sample of associated sources is on average at an active state compared to random samples. Conclusions. Based on our results we conclude that although it is clear that not all neutrino events are associated with strong radio flaring blazars, when we see large amplitude radio flares in a blazar at the same time as a neutrino event, it is unlikely to happen by random coincidence.

Testing the AGN Radio and Neutrino correlation using the MOJAVE catalog and 10 years of IceCube Data

“…In [5] it is argued that, if interactions are the cause of high-energy neutrinos then the gamma rays, produced in these photohadronic processes alongside with neutrinos, will interact with the same target photons to produce electron-positron pairs which will lead to a chain of processes resulting in gamma rays without enough energy to undergo pair production. This theory, which is also discussed by [6], can serve as a possible explanation for the lack of high energy gamma-ray (as observed by Fermi-LAT) and neutrino correlation in AGN and may hint towards a correlation with lower energy gamma-rays in the keV to GeV regime.…”

“…While our analysis fails to detect a significant signal (similar to [7]), it is important to continue the search for correlations (or a lack of it) between radio observations of AGN and neutrino data observed with IceCube. This can be done by analyses of individual sources (see for example [17] and [6]) or a stacked search similar to this work. While a time-dependent analysis making use of the same methodology described above but using lightcurves from MOJAVE will be discussed in a separate work soon, the limitations of the MOJAVE dataset imply that observations from other radio telescopes like the Owens Valley Radio Observatory [18] or F-GAMMA program [19] will have to be used to get a better understanding in the future (see also [4]…”

“…Multiple follow-up analyses have been launched in order to help us understand if AGN are responsible for the production of these astrophysical neutrinos, and how they are produced. Multi-messenger analyses like [3][4][5][6][7] which study the correlation of IceCube neutrinos with the observed electromagnetic radiation at different wavelengths from AGN help us understand the processes that could give rise to neutrinos in AGN.…”

“…Although the theories proposed by analyses like [4][5][6] are very promising, they are based on hints of radio-neutrino correlation with marginal statistical significance due to the limited data available. It makes it necessary to follow up with enough statistical power to test the authenticity of this correlation.…”

Inherent and Local Magnetic Field Structures in Jets from Active Galactic Nuclei

“…The presence of a net current along the jet axis implies different velocities for the positive and negative charges in the jet plasma. It is interesting in this connection that Plavin et al [37,38] and Hovatta et al [39] have recently argued that AGNs are likely sources of astrophysical neutrinos, and that this may, in turn, imply the presence of a significant admixture of highly energetic protons in the jet material. One possible origin for an inward jet current could be a slightly slower outflow velocity for the jet protons, compared to the jet electrons, but this is purely speculative at the moment.…”