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W. Yu, F. K. Lamb (U. Illinois), R. Fender (U. Southampton), M. van der Klis (U. Amsterdam)
We summarize the evidence concerning the mass, accretion geometry, and X-ray beaming of black hole and neutron star soft X-ray transients from nearly ten years of RXTE observations. The correlation between the peak luminosities of a low/hard state and a subsequent high/soft state during the rise of an outburst indicates that the flow powering the low/hard state is related to the flow powering the later high/soft state. The time lag between the two peaks is up to 100 days, suggesting that the connection between the flows producing the two states is in the outer disk. We argue that the mass in the disk affects the luminosity at which the state transition occurs and is responsible for the large differences in this luminosity among different outbursts of a given microquasar. We argue that emission from the jet contributes very little to the X-ray flux in the low/hard state. This implies that the luminosity at which the state transition occurs in ultra-luminous X-ray sources (ULXs) in nearby galaxies is a reliable indicator of the mass of the compact object and can be used to determine the nature of the ULX.
This work was supported in part by NSF grant AST 0098399, NASA grant NAG5-12030, and funds of the Fortner Endowed Chair at Illinois.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.