  We present a procedure to generally constrain the environments of
neutrino-producing sites in photomeson production models of jetted Active
Galactic Nuclei (AGN) where any origin of the dominant target photon field can
be accommodated. For this purpose we reconstruct the minimum target photon
spectrum required to produce the (observed) neutrino spectrum, and derive the
distributions of all corresponding secondary particles. These initiate
electromagnetic cascades with an efficiency that is linked to the neutrino
production rate. The derived photon spectra represent the minimum radiation
emerging from the source that is strictly associated with the
photo-hadronically produced neutrinos.
  Using the 2014-15 neutrino spectrum observed by IceCube from TXS 0506+056, we
conduct a comprehensive study of these cascade spectra and compare them to the
simultaneous multi-wavelength emission. For this set of observations, photopion
production from a co-spatially produced (co-moving) photon target can be ruled
out as well as a setup where synchrotron or Compton-synchrotron supported
cascades on a stationary (AGN rest frame) target photon field operate in this
source. However, a scenario where Compton-driven cascades develop in the
stationary soft-X-ray photon target which photo-hadronically produced the
observed neutrinos appears feasible with required proton kinetic jet powers
near the Eddington limit. The source is then found to produce neutrinos
inefficiently, and emits GeV photons significantly below the observed
Fermi-LAT-flux. Hence, the neutrinos and the bulk of the gamma rays observed in
2014/2015 from TXS 0506+056 cannot have been initiated by the same process.
