Strong surface outflows on accretion discs

Abstract

In order to provide an explanation for the unexpected radial brightness distribution of the steady accretion discs seen in nova-like variables, we have recently proposed that the accretion energy is redistributed outwards by means of strong, magnetically driven surface flows. In this paper we note that the "powerful, rotating disc winds" observed in the soft states of black hole X-ray binaries, and also in the disc around a magnetised neutron star in Her X-1, have the properties of the outflows we recently postulated to exist in the nova-like variable accretion discs around white dwarfs. The relevant properties are that the flows are not winds, but are instead bound flows (travelling at less than the escape velocity) and that the mass fluxes in the flows are a substantial fraction of the accretion rate in the disc.