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S. Markoff, M. A. Nowak (MIT Center for Space Research), J. Wilms (University of Warwick)
The hard state of X-ray binaries (XRBs) is characterized by a hard power law in the X-ray band, and a flat/inverted radio spectrum which is associated with occasionally imaged compact jets. The X-ray power law is generally thought to result from Compton upscattering of thermal accretion disk photons by a hotter phase of plasma called a corona. The corona properties are inferred from spectral characteristics thought to be both direct and reflected off the disk. It is interesting to note that the plasma conditions at the base of the observed jets, as inferred from conservation laws, are quite similar to that of the corona. Some corona models even invoke beaming away from the disk and larger roles for magnetic fields. The discovery of a tight correlation between the radio and X-ray luminosities in the hard state, as well as new evidence that the soft X-rays trace back to a break in the infrared/optical bands as predicted by synchrotron radiation, suggest that this idea may not be so farfetched. As a test of the strongest interpretation, we model the broadband spectrum of several simultaneous observations from XRBs, including Cyg X-1 and GX 339-4, assuming that all direct emission comes from the jet. We also include line and reflection features consistent with our models of reflection from jets. We present statistical fits to the broadband spectra, and discuss the results.
S.M. is supported by an NSF Astronomy & Astrophysics postdoctoral fellowship under NSF Award AST-0201597.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.