Irradiated Accretion Disk in the Galactic Supersoft X-Ray Source RX J0019.8 + 2156

Abstract

We considered the X-ray irradiated accretion disk in the galactic supersoft X-ray source RX J0019.8+2156, and estimated the contribution in UV and optical fluxes due to the reprocessing effect of X-ray radiation on the surface of the accretion disk and main sequence companion star. In the nuclear-burning white dwarf model of supersoft X-ray sources, radiation near the Eddington luminosity is generated on the white dwarf. For an assumed distance of 2 kpc to the object, however, a simple model with the standard accretion-disk model can not reproduce the observed fluxes in the UV and optical wavelengths of the object. This fact suggests the existence of reprocessing processes by the irradiated components in the binary system at relatively lower frequencies. We thus calculated the irradiation effects on the accretion disk and the mass donor companion in this system, and estimated their contributions to the flux of the lower frequency regions in the energy distribution. As a result, the reprocessed radiation from the irradiated accretion disk and companion star can well reproduce the observed fluxes.