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USA Observation of Spectral and Timing Evolution During the 2000 Outburst of XTE J1550-564

K. T. Reilly·E. D. Bloom·W. Focke·B. Giebels·G. Godfrey·P. M. Saz Parkinson·G. Shabad·P. S. Ray·R. M. Bandyopadhyay·K. S. Wood·M. T. Wolff·G. G. Fritz·P. Hertz·M. P. Kowalski·M. N. Lovellette·D. J. Yentis·Jeffrey D. Scargle
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Abstract

We report on timing and spectral observations of the 2000 outburst of XTE J1550-564 made by the Unconventional Stellar Aspect (USA) Experiment on board the Advanced Research and Global Observation Satellite (ARGOS). We observe a low-frequency quasi-periodic oscillation (LFQPO) with a centroid frequency that tends to increase with increasing flux and a fractional rms amplitude which is correlated with the hardness ratio. The evolution of the hardness ratio (4--16 keV/1--4 keV) with time and source flux is examined. The hardness-intensity diagram (HID) shows a cyclical movement in the clockwise direction and possibly indicates the presence of two independent accretion flows. We observe a relationship between the USA 4--16 keV count rate and radio observations and discuss this in the context of previously observed correlations between X-ray, radio, optical and IR data. We examine our results in the context of models invoking two accretion flows: a thin disk and a hot sub-Keplerian flow.

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K. T. Reilly, E. D. Bloom, W. Focke, B. Giebels, G. Godfrey, P. M. Saz Parkinson, G. Shabad, P. S. Ray, R. M. Bandyopadhyay, K. S. Wood, M. T. Wolff, G. G. Fritz, P. Hertz, M. P. Kowalski, M. N. Lovellette, D. J. Yentis, Jeffrey D. Scargle. 2001-07-28. USA Observation of Spectral and Timing Evolution During the 2000 Outburst of XTE J1550-564. https://doi.org/10.1086/324756

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