11 research outputs found
Rich Cluster and Non-Cluster Radio Galaxies & the (P,D) Diagram for a Large Number of FR I and FR II Sources
We present a comparison of the optical and radio properties of radio sources
inside and outside the cores of rich clusters from combined samples of more
than 380 radio sources. We also examine the nature of FR I and FR II host
galaxies, and in particular, we illustrate the importance of selection effects
in propagating the misconception that FR I's and FR II's are found in hosts of
very different optical luminosity. Given the large sample size, we also discuss
the power-size (P,D) distributions as a function of optical luminosity.Comment: to appear in Life Cycles of Radio Galaxies, ed. J. Biretta et al.,
New Astronomy Reviews; 6 pages, including 2 figure
Cosmological Magnetogenesis driven by Radiation Pressure
The origin of large scale cosmological magnetic fields remains a mystery,
despite the continuous efforts devoted to that problem. We present a new model
of magnetic field generation, based on local charge separation provided by an
anisotropic and inhomogeneous radiation pressure. In the cosmological context,
the processes we explore take place at the epoch of the reionisation of the
Universe. Under simple assumptions, we obtain results (i) in terms of the order
of magnitude of the field generated at large scales and (ii) in terms of its
power spectrum. The amplitudes obtained (B ~ 8.10^(-6) micro-Gauss) are
considerably higher than those obtained in usual magnetogenesis models and
provide suitable seeds for amplification by adiabatic collapse and/or dynamo
during structure formation.Comment: 9 pages, 2 figure
Chiral fermion mass and dispersion relations at finite temperature in the presence of hypermagnetic fields
We study the modifications to the real part of the thermal self-energy for
chiral fermions in the presence of a constant external hypermagnetic field. We
compute the dispersion relation for fermions occupying a given Landau level to
first order in g'^2, g^2 and g_phi^2 and to all orders in g'B, where g' and g
are the U(1)_Y and SU(2)_L couplings of the standard model, respectively, g_phi
is the fermion Yukawa coupling, and B is the hypermagnetic field strength. We
show that in the limit where the temperature is large compared to sqrt{g'B},
left- and right-handed modes acquire finite and different B-dependent masses
due to the chiral nature of their coupling with the external field. Given the
current bounds on the strength of primordial magnetic fields, we argue that the
above is the relevant scenario to study the effects of magnetic fields on the
propagation of fermions prior and during the electroweak phase transition.Comment: 11 pages 4 figures, published versio
Regular particle acceleration in relativistic jets
Exact solution is obtained for electromagnetic field around a conducting
cylinder of infinite length and finite radius, with a periodical axial current,
when the wave length is much larger than the radius of the cylinder. The
solution describes simultaneously the fields in the near zone close to the
cylinder, and transition to the wave zone. Proper long-wave oscillations of
such cylinder are studied. The electromagnetic energy flux from the cylinder is
calculated. These solutions could be applied for description of the
electromagnetic field around relativistic jets from active galactic nuclei and
quasars and particle acceleration inside jets.Comment: 12 pages, 1 figure. To appear in Proc. of the Workshop The
Multiwavelength Approach To Unidentified Gamma Ray Sources. The University of
Hong Kong - Hong Kong, China, 1-4 June 200
Stochastic Acceleration by Turbulence
The subject of this paper is stochastic acceleration by plasma turbulence, a
process akin to the original model proposed by Fermi. We review the relative
merits of different acceleration models, in particular the so called first
order Fermi acceleration by shocks and second order Fermi by stochastic
processes, and point out that plasma waves or turbulence play an important role
in all mechanisms of acceleration. Thus, stochastic acceleration by turbulence
is active in most situations. We also show that it is the most efficient
mechanism of acceleration of relatively cool non relativistic thermal
background plasma particles. In addition, it can preferentially accelerate
electrons relative to protons as is needed in many astrophysical radiating
sources, where usually there are no indications of presence of shocks. We also
point out that a hybrid acceleration mechanism consisting of initial
acceleration by turbulence of background particles followed by a second stage
acceleration by a shock has many attractive features. It is demonstrated that
the above scenarios can account for many signatures of the accelerated
electrons, protons and other ions, in particular He and He, seen
directly as Solar Energetic Particles and through the radiation they produce in
solar flares.Comment: 29 pages 7 figures for proceedings of ISSI-Bern workshop on Particle
Acceleration 201