ar X iv : a st ro - p h / 99 01 18 6 v 1 1 4 Ja n 19 99 IC EMISSION ABOVE A DISK

We developed a non-linear Monte Carlo code based on the LP method proposed by Stern et al (1995). We use it to simulate an extended non-thermal X/γ ray source coupled with a cold accretion disk. The source radiates by inverse Compton process. We show that very low optical depths (τ ∼ 5.10 −4) are required for the 2nd Compton order to be negligible. Such optical depths can be reached only if the source is very close to the disk (corona-like geometries). And even in this configuration, 2nd Compton order is negligible only for the hardest observed spectral slopes. We also account for Compton reflection on the disk. This kind of coupling leads to a strongly angle dependent spectrum with a reflection component much stronger than in standard isotropic models, leading to unobserved reflection dominated spectra at low inclination.