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

Recently Hardcastle & Worrall (MNRAS, 319, 562) 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.Comment: LaTeX uses aipproc.cls, 3 pages, 1 figure, to be published in Proc. Texas Symp. on Relativistic Astrophysics, Austin 200

Non-linear shock acceleration and high energy gamma rays from clusters of galaxies

Merger and accretion shocks in clusters of galaxies can accelerate particles via first order Fermi process. Since this mechanism is believed to be intrinsically efficient, shocks are expected to be modified by the backreaction of the accelerated particles. Such a modification might induce appreciable effects on the non--thermal emission from clusters and a suppression of the heating of the gas at strong shocks. Here we consider in particular the gamma ray emission and we discuss the capability of Cherenkov telescopes such as HESS to detect clusters at TeV energies.Comment: 6 pages, to appear in the proceedings of the Gamma 2004 Symposium on High Energy Gamma Ray Astronomy, Heidelberg, July 2004 (AIP Proceedings Series