2003ApJ...596..429O

We investigate the spectral energy distribution (SED) of the supercritical disk accretion flows around black holes by solving the multifrequency zeroth-moment equation of the radiation transfer equation under the flux-limited diffusion approximation as well as the energy equation of gas. Special attention is paid to the photon-trapping effects, the effects that photons are trapped within accretion flow and are swallowed by a black hole, with little being radiated away. It is found that when flow luminosity is below about twice the Eddington luminosity (L≲2L_E), photon trapping is ineffective and the SED shifts to the higher energy side as L increases. The peak frequency at which the SED reaches its peak becomes at maximum 3 times higher than that given by the standard-disk model, which might resolve the ``too hot accretion disk problem.'' When L≳2L_E, in contrast, the peak frequency of the SED tends to decrease with increase of mass accretion rate. This is due to enhanced photon trapping. Since high-energy photons are generated near the equatorial plane, they can be more effectively trapped in flow than low-energy ones, and hence the high-energy part of radiation is suppressed. Finally, the observed time variation of IC 342 S1, which is an ultraluminous X-ray source, in the X-ray H-R diagram, can be explained by the modulation of the mass accretion rate. In comparison with the observational data, we estimate that the mass of black hole in IC 342 S1 is ∼100M_☉.