4,308 research outputs found
On possible `cosmic ray cocoons' of relativistic jets
We consider effects on an (ultra-) relativistic jet and its ambient medium
caused by high energy cosmic rays accelerated at the jet side boundary. As
illustrated by simple models, during the acceleration process a flat cosmic ray
distribution can be created, with gyroradia for highest particles' energies
reaching the scales comparable to the jet radius or the energy density
comparable to the ambient medium pressure. In the case of efficient radiative
losses a high energy bump in the spectrum can dominate the cosmic ray pressure.
In extreme cases the cosmic rays are able to push the ambient medium off,
providing a `cosmic ray cocoon' separating the jet from the surrounding medium.
The considered cosmic rays provide an additional jet breaking force and lead to
a number of consequences for the jet structure and its radiative output. In
particular the involved dynamic and acceleration time scales are in the range
observed in variable AGNs.Comment: LaTeX (7 pages, 3 figures, uses mn.sty); MNRAS, accepte
Cosmic-Ray Acceleration at Ultrarelativistic Shock Waves: Effects of Downstream Short-Wave Turbulence
The present paper is the last of a series studying the first-order Fermi
acceleration processes at relativistic shock waves with the method of Monte
Carlo simulations applied to shocks propagating in realistically modeled
turbulent magnetic fields. The model of the background magnetic field structure
of Niemiec & Ostrowski (2004, 2006) has been augmented here by a
large-amplitude short-wave downstream component, imitating that generated by
plasma instabilities at the shock front. Following Niemiec & Ostrowski (2006),
we have considered ultrarelativistic shocks with the mean magnetic field
oriented both oblique and parallel to the shock normal. For both cases
simulations have been performed for different choices of magnetic field
perturbations, represented by various wave power spectra within a wide
wavevector range. The results show that the introduction of the short-wave
component downstream of the shock is not sufficient to produce power-law
particle spectra with the "universal" spectral index 4.2. On the contrary,
concave spectra with cutoffs are preferentially formed, the curvature and
cutoff energy being dependent on the properties of turbulence. Our results
suggest that the electromagnetic emission observed from astrophysical sites
with relativistic jets, e.g. AGN and GRBs, is likely generated by particles
accelerated in processes other than the widely invoked first-order Fermi
mechanism.Comment: 9 pages, 8 figures, submitted to Ap
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
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