  We study the frequently used assumption in multi-messenger astrophysics that
the gamma-ray and neutrino fluxes are directly connected because they are
assumed to be produced by the same photohadronic production chain. An
interesting candidate source for this test is the flat-spectrum radio quasar
PKS B1424-418, which recently called attention of a potential correlation
between an IceCube PeV-neutrino event and its burst phase. We simulate both the
multi-waveband photon and the neutrino emission from this source using a
self-consistent radiation model. We demonstrate that a simple hadronic model
cannot adequately describe the spectral energy distribution for this source,
but a lepto-hadronic model with sub-dominant hadronic component can reproduce
the multi-waveband photon spectrum observed during various activity phases of
the blazar. As a conclusion, up to about 0.3 neutrino events may coincide with
the burst, which implies that the leptonic contribution dominates in the
relevant energy band. We also demonstrate that the time-wise correlation
between the neutrino event and burst phase is weak.
