Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aas...206.4604n&link_type=abstract
American Astronomical Society Meeting 206, #46.04; Bulletin of the American Astronomical Society, Vol. 37, p.793
Astronomy and Astrophysics
Astronomy
Scientific paper
Previous work by Motch (1985) suggested that in the low/hard state of GX 339-4 the soft X-ray power-law extrapolated backward in energy agrees with the IR flux level. Corbel & Fender (2002) later showed that the typical hard state radio power-law extrapolated forward in energy meets the backward extrapolated X-ray power-law at an IR spectral break, which was explicitly observed twice in GX 339-4. This `IR coincidence' has been cited as further evidence that synchrotron radiation from a jet might make a significant contribution to the observed X-rays in hard state black hole systems. We quantitatively explore this hypothesis with a series of simultaneous radio/X-ray observations of GX 339-4, taken during its 1997, 1999, and 2002 hard states. We fit these spectra, in detector space, with a simple, but remarkably successful, doubly broken power-law model that indeed requires an IR spectral break. For these observations, the break position and the integrated radio/IR flux have stronger dependences upon the X-ray flux than the simplest jet model predictions. If one allows for a softening of the X-ray power law with increasing flux, then the jet model can agree with the observed correlation. We also find evidence that the radio flux/X-ray flux correlation previously observed in the 1997 and 1999 GX 339-4 hard states shows a `parallel track' for the 2002 hard state. The slope of the 2002 correlation is consistent with observations taken in prior hard states; however, the radio amplitude is reduced. We then examine the radio flux/X-ray flux correlation in Cyg X-1 through the use of 15 GHz radio data, obtained with the Ryle radio telescope, and Rossi X-ray Timing Explorer data, from the All Sky Monitor and pointed observations. We again find evidence of `parallel tracks', and here they are associated with `failed transitions' to, or the beginning of a transition to, the soft state. We also find that for Cyg X-1 the radio flux is more fundamentally correlated with the hard, rather than the soft, X-ray flux.
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