26 research outputs found
Acceleration in perpendicular relativistic shocks for plasmas consisting of leptons and hadrons
We investigate the acceleration of light particles in perpendicular shocks
for plasmas consisting of a mixture of leptonic and hadronic particles.
Starting from the full set of conservation equations for the mixed plasma
constituents, we generalize the magneto-hydrodynamical jump conditions for a
multi-component plasma, including information about the specific adiabatic
constants for the different species. The impact of deviations from the standard
model of an ideal gas is compared in theory and particle-in-cell simulations,
showing that the standard-MHD model is a good approximation. The simulations of
shocks in electron-positron-ion plasmas are for the first time
multi-dimensional, transverse effects are small in this configuration and 1D
simulations are a good representation if the initial magnetization is chosen
high. 1D runs with a mass ratio of 1836 are performed, which identify the
Larmor frequency \omega_{ci} as the dominant frequency that determines the
shock physics in mixed component plasmas. The maximum energy in the non-thermal
tail of the particle spectra evolves in time according to a power-law
proportional to t^\alpha with \alpha in the range 1/3 < \alpha < 1, depending
on the initial parameters. A connection is made with transport theoretical
models by Drury (1983) and Gargate & Spitkovsky (2011), which predict an
acceleration time proportional to \gamma and the theory for small wavelength
scattering by Kirk & Reville (2010), which predicts a behavior rather as
proportional to \gamma^2. Furthermore, we compare different magnetic field
orientations with B_0 inside and out of the plane, observing qualitatively
different particle spectra than in pure electron-ion shocks
Magnetic field amplification and electron acceleration to near-energy equipartition with ions by a mildly relativistic quasi-parallel plasma protoshock
The prompt emissions of gamma-ray bursts are seeded by radiating
ultrarelativistic electrons. Internal shocks propagating through a jet launched
by a stellar implosion, are expected to amplify the magnetic field & accelerate
electrons. We explore the effects of density asymmetry & a quasi-parallel
magnetic field on the collision of plasma clouds. A 2D relativistic PIC
simulation models the collision of two plasma clouds, in the presence of a
quasi-parallel magnetic field. The cloud density ratio is 10. The densities of
ions & electrons & the temperature of 131 keV are equal in each cloud. The mass
ratio is 250. The peak Lorentz factor of the electrons is determined, along
with the orientation & strength of the magnetic field at the cloud collision
boundary. The magnetic field component orthogonal to the initial plasma flow
direction is amplified to values that exceed those expected from shock
compression by over an order of magnitude. The forming shock is
quasi-perpendicular due to this amplification, caused by a current sheet which
develops in response to the differing deflection of the incoming upstream
electrons & ions. The electron deflection implies a charge separation of the
upstream electrons & ions; the resulting electric field drags the electrons
through the magnetic field, whereupon they acquire a relativistic mass
comparable to the ions. We demonstrate how a magnetic field structure
resembling the cross section of a flux tube grows in the current sheet of the
shock transition layer. Plasma filamentation develops, as well as signatures of
orthogonal magnetic field striping. Localized magnetic bubbles form. Energy
equipartition between the ion, electron & magnetic energy is obtained at the
shock transition layer. The electronic radiation can provide a seed photon
population that can be energized by secondary processes (e.g. inverse Compton).Comment: 12 pages, 15 Figures, accepted to A&
Gamma-Ray Bursts
Gamma-ray bursts are the most luminous explosions in the Universe, and their
origin and mechanism are the focus of intense research and debate. More than
three decades after their discovery, and after pioneering breakthroughs from
space and ground experiments, their study is entering a new phase with the
recently launched Swift satellite. The interplay between these observations and
theoretical models of the prompt gamma ray burst and its afterglow is reviewed.Comment: To appear in Rep. Prog. Phys., 74 pages, 11 figures, uses iopart.cls
macros; revisions and updated reference