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N. Bezayiff, D. M. Smith (University of California, Santa Cruz)
Recently it has been proposed by Titarchuk and Fiorito (2004, ApJ 612, 988; hereafter TF04) that the mass of a black hole candidate (BHC) can be deduced from a fit to the correlation between the x-ray spectral index and the frequency of a low-frequency quasi-periodic oscillation (QPO) in the x-ray flux, if a significant power-law component is present in the BHC's spectrum. This correlation was noted by Vignarca et al. (2003, A&A 397, 729) for several BHC. Using data from the Rossi X-ray Timing Explorer (RXTE), we will apply TF04's model to BHC GX 339--4 and see if a mass can be estimated for the compact object. GX 339--4 is an excellent candidate for this approach because 1) an abundance of data have been collected in the 2002 and 2004 outbursts when a significant power-law component is present, and 2) it is bright enough to provide sufficient statistics to reliably determine QPO center frequencies and the power-law index even in short pointings. The model of TF04 explains both the spectral variation and the QPO frequency as related to the radius of a transition layer between the outer (Keplerian) and inner (sub-Keplerian) disk. It has the potential both to explain these phenomena and to predict black hole masses from two robust and easily observed x-ray properties. In further work, we plan to apply this model to data from BHCs 1E 1740.7--2942 and GRS 1758--258.
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© 2004. The American Astronomical Society.