The influence of disc radiation capture upon black hole rotational evolution is negligible for radiatively inefficient discs. For the standard thin disc model it is a slight but potentially important effect leading to the equilibrium spin parameter v
alue of about 0.998. For optically thin discs, the fraction of disc radiation captured by the black hole is however about two times larger. In some disc radiation models, inner parts of the accretion flow are optically thin, advection-dominated flows, and the thin disc ends at some transition radius R_{tr}. The thermal energy of the disc stored in trapped radiation is released at this radius. Angular distribution of the radiation released at this radial photosphere facilitates its capture by the black hole. For accretion rates close to critical and disc truncation radius of (2..4) GM/c^2, radiation capture is most efficient in spinning the black hole down that may lead to a_{eq} ~ 0.996..0.997 or less depending on the mass accretion rate. For an accretion flow radiating some constant fraction epsilon of dissipated energy, the equilibrium Kerr parameter is shown to obey the relation 1-a_{eq} propto epsilon^{3/2} as long as 1-a_{eq} << 1. Deviations from Keplerian law near the last stable orbit dominate over the radiation capture effect if they exceed 1..2%.
Gravitational microlensing by the stellar population of lensing galaxies provides an important opportunity to spatially resolve the accretion disk structure in strongly lensed quasars. Some of the objects (like Einsteins cross) are reasonably consist
ent with the predictions of the standard accretion disk model. In other cases, the size of the emitting region is larger than predicted by the standard thin disk theory and practically independent on wavelength. This may be interpreted as an observational manifestation of an optically-thick scattering envelope possibly related to super-Eddington accretion with outflows.
We present the results of optical panoramic and long-slit spectroscopy of the nebula MF16 associated with the Ultraluminous X-ray Source NGC6946 ULX-1. More than 20 new emission lines are identified in the spectra. Using characteristic line ratios we
find the electron density n_e ~ 600cm^{-3}, electron temperature in the range from ~9000K to ~20 000K (for different diagnostic lines) and the total emitting gas mass M ~ 900 Msolar. We also estimate the interstellar extinction towards the nebula as A_V = 1.m54 somewhat higher than the Galactic absorption. Observed line luminosities and ratios appear to be inconsistent with excitation and ionization by shock waves so we propose the central object responsible for powering the nebula. We estimate the parameters of the ionizing source using photon number estimates and Cloudy modelling. Required EUV luminosity ($sim 10^{40}$ergl) is high even if compared with the X-ray luminosity. We argue that independently of their physical nature ULXs are likely to be bright UV and EUV sources. It is shown that the UV flux expected in the GALEX spectral range (1000-3000Angstroms) is quite reachable for UV photometry. Measuring the luminosities and spectral slopes in the UV range may help to distinguish between the two most popular ULX models.
