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S. Mineshige, K. Watarai (Kyoto), T. Manmoto (Chiba)
The observational properties of relativistic slim disks (or optically thick ADAFs; advection-dominated accretion flows) are discussed in comparison with those of thin disks and optically thin ADAFs. We first solve a transonic, slim disk structure in a general relativistic potential, and then calculate radiation spectra, taking into account photon redshift, Doppler boosting, gravitational lensing, and photon shielding by the inflated inner disk structure. The calculated spectra are fitted with multi-color blackbody model with fitting parameters of T\rm in, the maximum temperature of the blackbody, r\rm in, the (apparent) size of the innermost, hot region, and p, the power-law index of the radial temperature profile. We find that (i) for the disk around a Schwarzschild black hole r\rm in decreases from 3r\rm S to ~1.5 r\rm S (with r\rm S being the Schwarzschild radius) as mass-accretion rate increases beyond a critical value of ~30 L\rm E/c2; (ii) for the disk around a Kerr hole, conversely, r\rm in increases from < r\rm S to ~1.5 r\rm S as mass-accretion rate increases; (iii) at accretion rate above the critical value, therefore, disks around a Schwarzschild and Kerr BHs look quite similar and are hard to distinguish; and (iv) in both cases the temperature distribution gets flatter, from \propto r-3/4 at low luminosity to \propto r-1/2 at large luminosity. Implications on intermediate-mass black holes are briefly discussed. Interestingly, IC342 source 1 was observed to move along the line of decreasing r\rm in line as luminosity increases. This provides a firm evidence that at least some of intermediate luminosity sources are shining at \ga L\rm E and containing black holes with M ~q 10-100 M\odot.