  The high-peaked BL Lac object Pks2155-304 shows high variability at
multiwavelengths, i.e. from optical up to TeV energies. A giant flare of around
1 hour at X-ray and TeV energies was observed in 2006. In this context, it is
essential to understand the physical processes in terms of the primary spectrum
and the radiation emitted, since high-energy emission can arise in both
leptonic and hadronic processes. In this contribution, we investigate the
possibility of neutrino production in photo-hadronic interactions. In
particular, we predict a direct correlation between optical and TeV energies at
sufficiently high optical radiation fields. We show that in the blazar
Pks2155-304, the optical emission in the low-state is sufficient to lead to
photo-hadronic interactions and therefore to the production of high-energy
photons.
