SÉMINAIRE DU GRECO
"Transfert de la polarisation dans les plasmas magnétisés relativistes" 

Jean Heyvaerts 

Relativistic particles emit in magnetized media synchrotron radiation, the polarization state of which changes during propagation due to a number of effects. I'll show how all these effects can be accounted for in a radiativetransfertype equation for the vector of the four Stokes parameters. The dissipative part of the absorption matrix has been known as early as the 70's. By contrast, and surprizingly, the nondissipative transfer coefficients due to relativistic popula tions have prooved much more difficult to obtain, due to resonances at a very large number of harmonics of the relativistic cyclotron frequency and a complex mixture of quasiresonant and nonresonant interactions of the particles with the radiation. C.Pichon, S.Prunet, J.Thiébaut and myself have recently overcome these difficulties by use of an exact reformulation of the elements of the electrical high frequency conductivity tensor, which is related to the absorption matrix. These new analytical expressions have been brought to quasiexact and singularityless forms for frequencies much larger than the relativistic cyclotron frequency. Our results apply to any distribution of relativistic particles and reduce to simple forms in limiting cases. If time allows, I'll describe how multifrequency and imageresolved polarization data of synchrotronemitting sources can be inverted to provide 3D maps of the vector magnetic field in these source. The method has been demonstrated in J.Thiébaut's thesis by inverting simulation data representing the effect of propagation in a source made of a cold plasma and relativistic emitters. Our recent work should allow to extend it to fully relativistic sources, such as pulsar winds, blazars and possibly other highenergy sources.


lundi 15 avril 2013  11:00 Salle des séminaires François Arago, Institut d'Astrophysique de Paris 
