Collisionless shock physics: from non-relativistic to relativistic shocks


Astrophysical shock waves are ubiquitous in sources of high energy particles such as supernovae remnants, active galactic nuclei or gamma-ray bursts. In the first case, the shock waves are non- relativistic, while in the latter, they can be ultra-relativistic, yet a common point is the emission of non-thermal power-law spectra of high energy radiation, which is usually observed as synchrotron or Inverse Compton photons emitted by the accelerated electrons. Such radiation require the amplification of the magnetic field as turbulent fluctuations. One possibility is that the turbulent fluctuations are self-generated by the relativistic particles themselves. Theoretical studies as well as observational findings have brought to light the complex relationship that exists between the accelerated (non-thermal) particles, the dynamics and the structure of the shock wave, the surrounding magnetised turbulence and the efficiency of particle injection, actually the very nature of the acceleration process. This result is quite remarkable, as it means that the interpretation of current and forthcoming high resolution astrophysical data will teach us on the microphysics of collisionless shock waves, whether non-relativistic or ultra-relativistic. This is also highly challenging, because that relationship implies that (i) the process of acceleration is highly non-linear and must be considered in its full generality; that, furthermore, (ii) its comprehension must borrow knowledge from several disciplines (high energy astrophysics, particles physics and space plasma physics); and (iii) its study consequently requires the development of new numerical tools. This is the main objective of this working team, i.e., to assemble a trans-disciplinary community of physicists from these disciplines in order to study the physics of high energy radiation from shock waves, starting from the microphysics of the shock wave itself, hence discuss the development of numerical tools dedicated to these studies. The project will be mostly dedicated to the Fermi acceleration process at collisionless shocks. A special attention will be paid to the evolution of the performance of the process with respect to the shock velocity and to the physical properties of the environment (magnetization, magnetic field obliquity, degree of ionization). The following tasks will be considered during this project: 1/ effects of the turbulence properties over the Fermi acceleration process efficiency in relativistic shocks 2/ dominant plasma instabilities in various shock velocity and upstream magnetisation regimes 3/ connection between magnetospherical and astrophysical shock acceleration studies 4/ critical discussions on the available multiwavelength observations and prospects for future experiments.

List of participants

Program of the first Meeting: February 14th-18th 2011
Program of the second Meeting: April 23th-27th 2012

List of articles of interest including publications from team members

Please contact the team leader with any questions/corrections.