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G. J. Sobczak (Astronomy Dept., Harvard University), J. E. McClintock (Harvard-Smithsonian Center for Astrophysics), R. A. Remillard, A. M. Levine, E. H. Morgan (Center for Space Research, MIT), C. D. Bailyn (Department of Astronomy, Yale University), J. A. Orosz (Dept. of Astronomy and Astrophysics, The Pennsylvania State University)
Excellent coverage of the 1998 outburst of the X-ray Nova XTE J1550-564 was provided by the Rossi X-ray Timing Explorer. XTE J1550-564 exhibited an intense (6.8 Crab) flare on 1998 September 19 (UT), making it the brightest new X-ray nova observed with RXTE. We present a spectral analysis utilizing over 100 Proportional Counter Array spectra from 2.5-20 keV spanning more than 150 days, and a nearly continuous All Sky Monitor light curve. The spectra were fit to a model including multicolor blackbody disk and power-law components. XTE J1550-564 is observed in the very high, high/soft, and intermediate canonical outburst states of black hole X-ray novae. We also present correlations between the variable, low frequency (2-13 Hz) QPOs and the spectral parameters for XTE J1550-564 and compare these to similar correlations for the microquasar GRO J1655-40. The correlations are generally in the opposite sense for the two sources except that both sources exhibit a linear increase in the QPO frequency as the disk flux increases. This correlation implies that the QPO frequency is governed by the mass accretion rate in the disk.
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