Basic Properties of Supercritical Accretion Disks

Abstract

Abstract At the turn of the millennium, supercritical accretion disks (superdisks), where the mass-accretion rate highly exceeds the Eddington's one, are being resurrected under recent observational and theoretical progress. We examined the effects and properties of the self-irradiation, self-occultation, continuous and line spectra of superdisks, and found various distinct features of superdisks. Due to self-irradiation, the effective flux is enhanced by a factor of 1.1 to 1.8 all over the disk, depending on the relative disk thickness. For a superdisk with finite thickness, the flux at infinity is enhanced in the poleward direction, while it is zero in the equatorial direction. The continuous spectra are generally flat (vSv ∼ v0), as long as we see the disk pole-on. It, however, strongly depends on the inclination angle: for a larger inclination angle the central part of the disk is self-occulted and the flat nature of the continuum disappears. The line spectra are also greatly modified from those of the standard disk. In the non-relativistic standard model the line spectra have symmetrical double peaks. In the superdisk, however, the line spectra become asymmetric with strong blue peaks and weak red peaks, even for the non-relativistic case. This is due to the projection effect. The relations between the observables and model parameters are derived.