Understanding of X-ray spectra of black hole binaries and its application to ULXs

Based on X-ray spectral analyses of RXTE data, we report on understanding of accreting stellar black holes in high mass accretion rate. We have found that there are three spectral regimes for black hole binaries in the (stable) high/soft state. Well established standard regime satisfies the standard relation that Z_disk is proportional to T_in⁴ (L_disk is disk bolometric luminosity and T_in is disk inner temperature). In an apparently standard regime, though the spectrum is dominated by the disk emission like in the standard regime, L_disk is moderately saturated and another cooling process is required in addition to radiative cooling. An intermediate anomalous regime or (relatively weak) very high state was characterized by highly comptonized spectrum by high energy electrons. The quasi-periodic oscillations are observed preferentially in the anomalous regime. This presented picture was found to explain the spectral behavior of both black hole binaries in our Galaxy and LMC. Spectral evolution of several bright ULXs observed with ASCA was also successfully explained in the same picture.