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W. Cui (Purdue University), F. Yuan (Purdue University and Shanghai Astronomical Observatory)
Most black hole candidates (BHCs) are transient X-ray sources -- they are extremely faint in quiescent but, once in a long while, becomes the brightest X-ray sources in the sky during an outburst. The evolution of a BHC throughout an outburst is often empirically characterized by a set of discrete states, such as the well-known low/hard and high/soft states. Though crude, the approach has been very useful in revealing qualitative differences among various stages of the evolution and thus the underlying physical processes involved. In comparison, the quiescent state is the least understood observationally, due to the lack of high-quality data. It is tempting to view it as a simple extension of the low/hard state in the direction of low mass accretion rates, given that the X-ray spectrum of BHCs in the later state is well described by the inverse-Compton scattering of soft photons by energetic electrons in hot accretion flows or some sort of hot coronae. Here, we argue that this is probably not the case, based on results from an investigation of the roles of accretion and jets in producing the observed radiation from radio to X-ray wavelengths.
This work was supported in part by NASA Grants NAG5-9998 and NNG05GF91G and the One-Hundred Talent Program of China.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.