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M. D. Still (NASA/GSFC, University of St Andrews), K. O'Brien, K. Horne (University of St Andrews)
Accretion disks are the engines driving the exotic phenomena observed in X-ray binary stars. The physical structure of disks feeding neutron stars or stellar mass black holes is pooly understood because they are too distant to resolve directly and are often low-luminosity sources compared to their stellar hosts and companions. Consequently ideas concerning the nature of disks in X-ray binaries such as advection-dominated accretion flows, irradiation-induced warping, tidal distortions and flip-flop instabilities remain untested. We have developed "Echo-tomography" to address this problem. We employ simultaneous monitoring of X-ray pulse or flare events from the compact source and their subsequent echoes at lower energies which result from reprocessing by the atmospheres of the companion star and accretion disk. Reprocessed pulses are delayed from the X-ray events due to light travel times across the binary. The result is a transfer function which defines an iso-delay curve over the surface of the reprocessing atmospheres. Samples of curves can be built up over an orbital cycle to produce a spatial map of disk structure using inversion techniques. The nature of this type of experiment requires the use of multiple satellites and ground-based observatories, but with the suite of X-ray and optical instruments comprising the payload onboard the upcoming X-ray Multi-Mirror Mission, echo-tomography will be feasible from a single observatory.
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The author(s) of this abstract have provided an email address for comments about the abstract: martin.still@st-and.ac.uk