X‐ray energy spectra from accretion disks in black hole candidates

I will review major accretion disk spectral models which have been used to fit observed x‐ray spectral of black hole candidates and low mass x‐ray binaries. These spectral models are compared in the light of recent observations of luminosity/spectral variations of black hole candidates. Blackbody disk models can explain the observed luminosity/spectral variations in terms of variation of the mass accretion rate and constant mass of the central object, although the local emission of accretion disk will not be a blackbody. Because of the Comptonization, color temperature of the local emission will be significantly larger than the effective temperature, and success of the blackbody disk model suggests the color to the effective temperature ratio (Tcol/Teff) is constant along the disk and radius and disk luminosity variations. Precise calculation of accretion disk spectral models by Titarchuk (1993) taking account of Comptonization and radiative transfer reproduced the observed results successfully.