  Extragalactic jets are the most powerful persistent sources of the universe.
Those pointing at us are called blazars. Their relativistically boosted
emission extends from radio frequencies to TeV energies. They are also
suspected to be the sources of energetic neutrinos and high energies cosmic
rays. The study of their overall spectrum indicates that most of the emission
of powerful blazars is in hard X-rays or in soft gamma-rays. In this band we
can find the most powerful jets, visible also at high redshifts. It is found
that the jet power is linked to the accretion luminosity, and exceeds it,
especially if they produce energetic neutrinos, that require the presence of
ultrarelativistic protons.
