Geometry of accretion in Soft X-ray Transients

Abstract

We present results of modelling Ginga data of a number of Soft X-ray Transient sources performed with the aim of constraining the geometry of accretion during various stages of the sources' evolution. Assuming a generic geometry of a central, extended X-ray source with an external, optically thick accretion disk, we use consistent models of X-ray reprocessing to constrain the inner radius of the accretion disk and its ionization state. We show that the evolution of GS 1124-68 (Nova Muscae 1991) and GS 2000+25 agree qualitatively with the recent ideas linking the high/low state transition with changing the inner radius of the optically thick disk, but the case of GS 2023+33 (V404 Cyg) poses a problem for any model.

Aipproc LaTeX (4 pages, 4 figures), to appear in Proc. of the 8th October Astrophysics Conference in Maryland, "Accretion Processes in Astrophysical Systems", S. S. Holt & T. Kallman (eds.)