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W. B. Focke, Y. Jiang, D. M. Tournear, E. D. Bloom, B. Giebels, G. Godfrey, P. Saz Parkinson, K. T. Reilly (Stanford), G. Shabad (iStanford Linear Accelerator Center, Stanford U.), K. S. Wood (NRL), R. M. Bandyopadhyay (Oxford), G. Fritz, P. Hertz (NASA HQ), M. P. Kowalski, M. N. Lovellette, P. S. Ray, M. T. Wolff (NRL), D. J. Yentis (E. O. Hurlbert Center for Space Research, NRL), J. D. Scargle (NASA/Ames Research Center)
Uttley & McHardy (MNRAS, 323, L26, 2001) demonstrated a simple new diagnostic of variability in accreting sources. It involves the relation of the RMS (absolute, not fractional) variability of the source to its luminosity. They observed a linear relation in a black hole candidate and a neutron star, and observed behavior consistent with such a relation in an active galactic nucleus.
We explore and expand on this diagnostic. The diagnostic is applied to data collected with ARGOS/USA and RXTE/PCA data for Cygnus X-1 and other accretion powered X-ray sources. We find that a two-dimensional distribution is necessary to describe the data. We apply the diagnostic to model light curves to constrain models of the time variability of the sources.
Work at SLAC was supported by Department of Energy contract DE-AC 03-76-SFO0515. Basic research in X-ray astronomy at the Naval Research Laboratory is supported by ONR/NRL. This work was also supported by the NASA Applied Information Systems Research Program.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.