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Compton Scattering by Static and Moving Media I. The Transfer Equation and Its Moments  Dimitrios Psaltis
; Frederick K. Lamb
;  Date: 
3 Jun 1997  Subject:  astroph  Affiliation:  Univ. of Illinois at UrbanaChampaign  Abstract:  Compton scattering of photons by nonrelativistic particles is thought to play an important role in forming the radiation spectrum of many astrophysical systems. Here we derive the timedependent photon kinetic equation that describes spontaneous and induced Compton scattering as well as absorption and emission by static and moving media, the corresponding radiative transfer equation, and their zeroth and first moments, in both the system frame and in the frame comoving with the medium. We show that it is necessary to use the correct relativistic differential scattering cross section in order to obtain a photon kinetic equation that is correct to first order in epsilon/m_e, T_e/m_e, and V, where epsilon is the photon energy, T_e and m_e are the electron temperature and rest mass, and V is the electron bulk velocity in units of the speed of light. We also demonstrate that the terms in the radiative transfer equation that are secondorder in V usually should be retained, because if the radiation energy density is sufficiently large compared to the radiation flux, the effects of bulk Comptonization described by the terms that are secondorder in V are at least as important as the effects described by the terms that are firstorder in V, even when V is small. Our equations are valid for systems of arbitrary optical depth and can therefore be used in both the freestreaming and the diffusion regimes. We demonstrate that Comptonization by the electron bulk motion occurs whether or not the radiation field is isotropic or the bulk flow converges and that it is more important than thermal Comptonization if V^2 > 3 T_e/m_e.  Source:  arXiv, astroph/9706017  Services:  Forum  Review  PDF  Favorites 


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