X-Ray Spectra at Infinity from a Relativistic Accretion Disk around a Kerr Black Hole

Abstract Some of the existing compact X-ray sources might be Kerr black holes surrounded by accretion disks that emit blackbody radiation. We have calculated the spectra and the flux at infinity emitted from an optically thick and geometrically thin relativistic accretion disk around a Kerr black hole. If one observes the spectrum characteristic to a Kerr black hole, both the specific angular momentum of the black hole and the inclination angle of the disk can be estimated when either the distance to the hole or the accretion rate and the mass of the hole are already known through other observations. We also calculated the apparent light curve observed at infinity from a hot spot co-moving with a disk. When the specific angular momentum of the black hole is sufficiently large enough and the disk is nearly edge-on, the light curve exhibits an almost rectangular pulse shape. This pulse profile for Kerr black holes is much in contrast to that for the Schwarzschild types.