USA Experiment Observation of Spectral and Timing Evolution during the 2000 Outburst of XTE J1550–564
/ Authors
K. Reilly, E. Bloom, W. Focke, B. Giebels, G. Godfrey, P. S. Saz Parkinson, and G. Shabad, P. Ray, R. Bandyopadhyay, K. Wood
and 7 more authors
M. Wolff, G. Fritz, P. Hertz, M. Kowalski, M. Lovellette, and D. J. Yentis, andJeffrey D. Scargle
/ 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 with a centroid frequency that tends to increase with increasing flux and a fractional rms amplitude that is correlated with the hardness ratio. Several high-frequency quasi-periodic oscillations were detected by Rossi X-Ray Timing Explorer during periods where the low-frequency quasi-periodic oscillation was seen to be weakening or not detectable at all. The evolution of the hardness ratio (4-16 keV/1-4 keV) with time and source flux is examined. The hardness-intensity diagram shows a cyclical movement in the counterclockwise direction and possibly indicates the presence of two independent accretion flows: a thin-disk flow and a hot sub-Keplerian flow.
Journal: The Astrophysical Journal Letters
DOI: 10.1086/324756