X-ray spectra of accreting black holes (both supermassive and stellar mass ones) can be deconvolved into a power-law produced by thermal Comptonization and a components due to the reflection of hard X-rays from cold material (presumably the accretion disc). In some sources, the amount of reflection is much below the value corresponding to an X-ray source above a flat infinite reflector. It was suggested that the lack of reflection is due to mildly relativistic bulk motion of the coronal plasma away from the reflector. Bulk motion causes aberration reducing the X-ray emission towards the disc, which leads to smaller reflection. This model predicts a correlation between the spectral slope and the amount of reflection that successfully reproduces the recently observed correlation.
Galactic black holes (GBH) radiate in one of several spectral states. In the soft state the spectra extend up to at least 1 MeV without a spectral break. Such a behaviour contradicts the standard thermal Comptonization picture. A hybrid, thermal/non-thermal model was developed where such spectra are produced by Comptonization of soft photons from the cool accretion disc by non-thermal electrons in the corona.
GBHs also show time lags between the variability in different energy bands. These lags sometimes become as large as 0.3 sec. A model was proposed where the time lags are related to the time scales of the spectral evolution of magnetic flares which may be comparable to the Keplerian time scales at 3-100 gravitational radii from the central black hole. The proposed model describes well the time-averaged spectra as well as the temporal characteristics such as the power-density spectrum, the time/phase lags, and the coherence function of Cygnus X-1.
Some quasars demonstrate mysterious steep rises in polarization blueward of the Lyman limit. It was shown that strong rises in polarization can be produced in the plasma outflowing from the accretion disc with mildly relativistic velocities and by an ionized ``skin'' covering the disc.