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).