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E. Kalemci, J. A. Tomsick, R. E. Rothschild (CASS/UCSD)
We have used RXTE to obtain power spectra for the Galactic black hole candidate XTE J1550-564 in several energy bands to study the low frequency quasi-periodic oscillations (QPOs). The properties of these QPOs have been extensively studied at lower energies (3 - 15 keV) by the PCA instrument on-board RXTE but not as much for higher energies. We focus on HEXTE instrument on RXTE which has a bandpass of 15-200 keV. We developed a technique to correct for the dead-time effects in HEXTE power spectrum, and have been able to detect or obtain useful upper limits for the QPOs with frequencies from 0.1 to 5 Hz in several observations in the 60-120 keV range. The goal of this study is to determine the relationship between the QPO strength and energy, and how it varies from observation to observation. This relationship may have important implications for the accretion disk geometry and temperature profile of the corona.