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Session 104 - Accretion-Powered X-Ray Sources.
Display session, Thursday, January 18
North Banquet Hall, Convention Center
In this paper we analyze the plane-parallel flow of a radiation-dominated gas, including the effects of energy losses driven by the escape of radiation from the flow. This scenario may be dynamically important in radiation-dominated accretion columns above neutron stars and also in radiation-dominated accretion disks around black holes. In these environments, the mass and momentum fluxes are conserved while the gas crosses the shock, but the energy flux is not. When radiative losses are included in the calculation, the flow stagnates in the downstream region. This behavior is consistent with that expected when accreting gas is confronted by a barrier, such as the solid surface of a neutron star, or the centrifugal ``wall'' surrounding a black hole. Paradoxically, our results indicate that the incorporation of radiation escape into the model causes the downstream radiation pressure to increase, with an associated hardening of the spectrum. The increased pressure reflects the requirement that the radiation field must brake the gas to a standstill. The new model may improve our understanding of the spectral formation process in high-luminosity accretion flows around neutron stars and black holes.
