Observational evidence for the origin of high-energy neutrinos in
  parsec-scale nuclei of radio-bright active galaxies
  Observational information on high-energy astrophysical neutrinos is being
continuously collected by the IceCube observatory. However, the sources of
neutrinos are still unknown. In this study, we use radio very-long-baseline
interferometry (VLBI) data for a complete VLBI-flux-density limited sample of
active galactic nuclei (AGN). We address the problem of the origin of
astrophysical neutrinos with energies above 200 TeV in a statistical manner. It
is found that AGN positionally associated with IceCube events have typically
stronger parsec-scale cores than the rest of the sample. The post-trial
probability of a chance coincidence is 0.2%. We select the four strongest AGN
as highly probable associations: 3C 279, NRAO 530, PKS 1741-038, and PKS
2145+067. Moreover, we find an increase of radio emission at frequencies above
10 GHz around neutrino arrival times for several other VLBI-selected AGN on the
basis of RATAN-600 monitoring. The most pronounced example of such behavior is
PKS 1502+106. We conclude that AGN with bright Doppler-boosted jets constitute
an important population of neutrino sources. High-energy neutrinos are produced
in their central parsec-scale regions, probably in proton-photon interactions
at or around the accretion disk. Radio-bright AGN that are likely associated
with neutrinos have very diverse gamma-ray properties suggesting that
gamma-rays and neutrinos may be produced in different regions of AGN and not
directly related. A small viewing angle of the jet-disk axis is, however,
required to detect either of them.
