126 research outputs found
Cosmic ray transport in self-excited turbulence
No full textFirst order Fermi acceleration at the outer shocks of supernova remnants is believed be an efficient process. If this is indeed true, the effect of the cosmic-ray pressure on the uid properties of the upstream plasma, can not be neglected. It is well known that the resulting pressure gradient leads to the production of an extended shock precursor. It has been suggested by Bell (2004) that cosmic rays in the precursor will also have a strong in uence on the macroscopic properties of the magnetic field. Observational evidence of bright X-ray synchrotron rims in several young supernova support this theory. Amplification of the magnetic field beyond the linear regime, via the non-resonant current driven instability is investigated. We report on numerical calculations of magnetic field growth and the resulting transport properties of relativistic particles in the amplified field
The amplification of magnetic fields in parallel shocks
No full textThe amplification of magnetic fields due to plasma instabilities in various energetic environments is a crucial issue for our understanding of particle acceleration and the observed emission from these regions. This process is supported both by observations of large magnetic fields close to the outer shocks of supernova remnants and also by the theoretical motivation to explain the origin of galactic cosmic rays. The so-called non-resonant current driven instability seems to be a likely mechanism capable of driving such strong amplification. The role of this instability in various environments is reviewed, and recent results from numerical simulations are presented
Supernova remnants and the effect of efficient cosmic ray acceleration
No full textIt is well known that electrons and probably cosmic rays are accelerated in supernova remnants. To maintain the observed steady galactic cosmic-ray spectrum, it is necessary that they be very efficient accelerators. The back reaction of the high-energy particles on the shock structure and environment are reviewed with a particular emphasis on the amplification of magnetic fields
Particle acceleration in young SNRs and the spherical box model
No full textWe investigate the electron spectrum at a spherically symmetric blast wave during the early free expansion phase as the shock propagates into the progenitor stellar wind environment. This is done by developing the spherical box model. In order to include the effect of nonlinear self-excitation of MHD waves the magnetic field is approximated by the Bell-Lucek effect for young supernovae. This results in a much larger value for the field than in the quasilinear regime. This field is subsequently frozen into the downstream flow. We calculate the synchrotron and X-ray emission and compare with observations. © 2005 American Institute of Physics
MAGNETIC FIELD GENERATION BY BIERMANN BATTERY AND WEIBEL INSTABILITY IN LABORATORY SHOCK WAVES
No full textMagnetic field generation in the Universe is still an open problem. Possible mechanisms involve the Weibel instability, due to anisotropic phase-space distributions, as well as the Biermann battery, due to misaligned density and temperature gradients. These mechanisms can be reproduced in scaled laboratory experiments. In this contribution we estimate the relative importance of these two processes and explore the laser-energy requirements for producing Weibel dominated shocks. © The Author(s) 2013
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