II. The Compton-reflected Continuum

Guilbert & Rees (1988) and Lightman & White (1988) were the first to imagine that Compton reflection could be the mechanism generating the emission bump at high energies that is observed in Seyfert galaxies and that cannot be otherwise explained as thermal emission from the (standard, "cold") disc.
For the emitted spectra we used a code which simulates such reflection following standard assumptions on the disc structure and ionization (Matt et al. 1991; see also Ross & Fabian 1993 for a calculation of the backscattered continuum for various ionization states of the disc). Such assumptions can be changed and other accretion models can of course be considered, but here we deal for simplicity only with standard keplerian, geometrically thin and optically thick discs.

Figure 1 shows broad-band (E=2-250 keV) spectra (in red) corresponding to Schwarzschild and extreme Kerr BHs, for different values of the view angle (observer's inclination with respect to the simmetry axis of the system), an emitting region going from the innermost stable orbit up to 100 gravitational radii, and a simple power law for the disc emissivity (i.e. radial dependence) with index -0.5. Logarithmic scales on both axes are used.

Apart from the iron line, which is not very well resolved here, the overall shape of the continuum is clearly seen to be spread through, more and more "enlarged" with increasing inclination, as an effect of the Doppler shift of the photons.
In another picture (figure 2) we show the overall effect on the continuum emission alone.

The large spread in blue- or red-shifts also results in a smearing of the photoelectric edge into broad throughs, as also predicted by Ross et al. 1996. This can be better seen with an increased resolution in energy (next section).