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M.J. Pierce (University of Wyoming), W.C. Cash (University of Colorado)
Recent technological developments suggest that space-based interferometry at X-ray wavelengths is feasible. At these wavelengths nano-arcsecond astrometry is be possible with modest, 2-km, baselines. We discuss the prospects for using this capability for high-precision, astrometric measurements of X-ray luminous quasars. The space motion of the Earth with respect to the Cosmic Microwave Background is well characterized and provides an ideal reference frame for such measurements. In particular, it induces a differential parallax for chance alignments of quasars located at different redshifts. We show that the fringes can in principle be measured and that the resulting signal is ideally suited for characterizing the equation of state of dark energy as a function of redshift. The geometric nature of this approach offers a number of advantages over alternative methods. We present a baseline concept for a space-based X-ray interferometer capable of making these measurements and discuss some of the possible technical difficulties with this technique. We also discuss some of the systematic errors with this approach. These include the effects of the transverse peculiar motions of the quasar host galaxies and of gravitational lensing by intervening galaxy halos. We conclude that high-precision astrometry of X-ray luminous quasars offers great promise for characterizing the dark energy content of the universe.
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Bulletin of the American Astronomical Society, 36 #2
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