Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011sf2a.conf...39p&link_type=abstract
SF2A-2011: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics Eds.: G. Alecian, K. Belkacem,
Astronomy and Astrophysics
Astrophysics
High Energy Astrophysics, Fermi Acceleration, Turbulence, Uhe-Cosmic Rays, Snrs, Grbs, Jets
Scientific paper
High energy astrophysical phenomena stem from the generation of powerful flows emanating from Super Nova explosions, Gamma Ray Bursts, from ejections in the environment of Black Holes or Neutron Stars that lead to the formation of very strong shocks where particle acceleration takes place. The new developments in these issues are based on the interdependence between the shock structure, the generation of supra-thermal particles and the generation of turbulence. This view started with the studies of Super Nova Remnants, both with X-ray observations and with theoretical investigations, that concluded that the magnetic field is largely amplified by MHD instabilities in the precursor. It is thought, and numerical simulations support that view, that the penetration of supra-thermal particles in the shock precursor generates a magnetic turbulence which in turn produces the scattering process needed for particle acceleration through the Fermi process. This successful development inspired similar investigations for the termination shock of Gamma Ray Bursts. However in ultra-relativistic shocks, difficulties arise with the transverse magnetic field that puts a limitation to particle penetration upstream and that drags particles in the downstream flow and makes shock recrossing difficult. It turns out that only fast enough micro-turbulence can make the Fermi process operative when its level is high enough. This very challenging requirement can nevertheless be fulfilled naturally, as proved by recent numerical simulations. These points are briefly discussed in the presentation and astrophysical consequences are drawn. In particular, it is shown that ultra-relativistic shocks are very efficient electron accelerators and radiation emitters, but poor proton accelerators. It turns out that mildly relativistic shocks inside relativistic flows are better candidates for the generation of UHE-Cosmic Rays. The acceleration performance depends essentially of two parameters: the conversion factor of incoming energy at a shock into magnetic turbulence (this number is provided by the numerical simulations) and the jet power. The Pierre Auger Observatory suggests that the UHECR spectrum is enriched with heavy elements at high energies. What we know about the closest Radio-jets, as those of Centaurus A, together with the theoretical view, indicates that UHECRs can be accelerated up to a few Z × 10^{18} eV, and iron nuclei (Z=26) from these nearby radio galaxies can populate the UHE-Cosmic Rays, as long as they are not photo-dissociated. Nevertheless a significant proton contribution can come from GRB internal shocks as well.
Lemoine Martin
Pelletier Guy
No associations
LandOfFree
Particles acceleration at relativistic shocks and high energy astrophysics does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Particles acceleration at relativistic shocks and high energy astrophysics, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Particles acceleration at relativistic shocks and high energy astrophysics will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1439310