Pressure imbalance of FRII radio source lobes: a role of energetic proton population

Recently Hardcastle & Worrall (2000) analyzed 63 FRII radio galaxies imbedded in the X-ray radiating gas in galaxy clusters and concluded, that pressures inside its lobes seem to be a factor of a few lower than in the surrounding gas. One of explanations of the existing ‘blown up’ radio lobes is the existence of invisible internal pressure component due to energetic cosmic ray nuclei (protons). Here we discuss a possible mechanism providing these particles in the acceleration processes acting at side boundaries of relativistic jets. The process can accelerate particles to ultra high energies with possibly a very hard spectrum. Its action provides also an additional viscous jet breaking mechanism. The work is still in progress. I PARTICLE ACCELERATION AT THE JET BOUNDARY For particles with sufficiently high energies the transition layer between the jet and the ambient medium can be approximated as a surface of discontinuous velocity change, a tangential discontinuity (‘td’). If particles’ gyroradia (or mean free paths normal to the jet boundary) are comparable to the actual thickness of this shear-layer interface it becomes an efficient cosmic ray acceleration site provided the considered velocity difference, U , is relativistic and the sufficient amount of turbulence is present in the medium. The problem was extensively discussed in early eighties by Berezhko with collaborators (see the review by Berezhko 1990) and in the diffusive limit by Earl et al. (1988) and Jokipii et al. (1989). The case of a relativistic jet velocity was considered by Ostrowski (1990, 1998, 2000). The simulations (Ostrowski 1990, cf. Bednarz & Ostrowski 1996 for shock acceleration) show that in favorable conditions the acceleration process acting at relativistic tangential discontinuity of the velocity field can be very rapid, with the time scale