Monte-Carlo simulations of comptonization on free-falling electrons

The recent observations of black hole binary systems show more and more cle arly that the observed spectra of these systems result from the Comptonizat ion of the high energy electrons close to the black hole on the ambient sof t photons. So, in order to model these observed spectra, we have to treat a s precisely as possible the Comptonization process, taking into account the real motion of the electrons, which is, in fact, a composition of their fr ee-falling motion onto the black hole and of their brownian motion due to t he electron temperature. Whereas the thermal Comptonization has been alread y explored in details. the effects of the electrons free-falling motion on the resulting Comptonized spectrum is not yet clearly understood. Also, the general relativistic effects close to the black hole were not yet plainly taken into account. We present the study of these effects by using a Monte- Carlo simulation which take into account the exact motion of the Comptonizi ng electrons, in a fully general relativistic treatment. Some of the result s of this study will be presented here, and will give a new insight into th e understanding of black hole binary spectral states.