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states, combining a still powerful jet and a luminous accretion disk. In these states, disk photons can be scattered
up to very high energy by non thermal particles from the jet, which would produce enough gamma-ray photons
to trigger pair production. Detailed quantitative calculations are under work.
In another work, with the PhD student Cl?ment Cabanac, we are studying the time behavior of X-ray
binaries observed with the hard X and γ-rays satellite INTEGRAL. We are currently developing numerical
tools to extract the time information from the raw data, especially the presence of quasi-periodic oscillations
(QPO) that have been commonly detected by the RXTE satellite. The origin of these QPO is still disputed
and an important question is their energy spectrum. We are developing in parallel a theoretical model for these
QPO based on an instability at the transition region between the SAD and the JED.
15.6 Relativistic Plasmas and Cosmic Rays
The non-thermal radiation from Black Hole environments is emitted by a relativistic plasma generated in the
jets. Therefore high energy radiation (including TeV gamma rays, cosmic rays and possible neutrinos) is an
important consequence of accretion-ejection flows around Black Holes. These relativistic plasmas are generated
by specific dissipation mechanisms occurring at relativistic shocks and magnetic reconnections that require some
theoretical developments. Moreover the dynamics of these accretion-ejection flows cannot be fully mastered
without a significant understanding of these microphysics processes. Some progress have been recently done in
our team on these topics which are at the forefront of the physics of the so-called ”Astroparticle Science”.
15.6.1 Relativistic plasmas
Relativistic aspect of the accretion-ejection phenomenon.
The issue of the formation of relativistic jets involves three important intricate problems, namely, the crossing
of critical surfaces, collimation and conversion of the Poynting flux into matter-energy flux. These problems
have been addressed in a synthesis that will appear in a collective book organized by R. Blandford and M.
Lyutikov (Pelletier 2005).
A major problem of the physics of accretion disks is the excitation of a turbulence state able to efficiently
transfer the angular momentum of matter in order that it progressively falls on the central Black Hole. In the
nineties, a successful solution has been proposed with the so-called ”Magneto-Rotational Instability”. We have
extended the analysis of the instability to the case of a Kerr Black Hole and found an expected intensification
and a wider window of the instability, that makes it compatible with the intense magnetic field required for
launching jets, despite the stabilizing tendency of its tension effect. The analysis has been presented in the
same chapter as before and will be developed in a forthcoming paper.
Magnetic reconnection in relativistic regime.
Nowadays the process of ”magnetic reconnection” is invoked in order to convert Poynting flux into matter
energy flux and radiation in ultra-relativistic flows. Only very fast reconnection processes can be relevant in this
context. Now standard reconnection processes based on the generalization of the Sweet-Parker scheme are too
slow. New investigations in Tokamaks and space plasma physics revealed a new mechanism that turns out to be
independent on dissipation and fast. We are extending this approach to relativistic plasmas. A fair description
of the phenomenon can be obtained in the frame of an appropriate modification of relativistic MHD for both
baryon loaded plasmas and e + − e − -plasmas. This has been presented in a first publication (Pelletier 2005) and
a paper on relativistic reconnection is to be submitted (Pelletier & Longaretti 2005).
15.6.2 Cosmic Rays
Transport of Cosmic Rays in chaotic magnetic fields.
The properties of the transport of Cosmic Rays in weak turbulence theory are known since the seventies.
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