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The Off State of GX 339-4

A. K. H. Kong·E. Kuulkers·P. A. Charles·L. Homer
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Abstract

We report BeppoSAX and optical observations of the black hole candidate GX 339-4 during its X-ray `off' state in 1999. The broad-band (0.8-50 keV) X-ray emission can be fitted by a single power law with spectral index, α~1.6. The observed luminosity is 6.6e33 erg s^{-1} in the 0.5-10 keV band, which is at the higher end of the flux distribution of black hole soft X-ray transients in quiescence, comparable to that seen in GS 2023+338 and 4U 1630-47. An optical observation just before the BeppoSAX observation shows the source to be very faint at these wavelengths as well (B=20.1, V=19.2). By comparing with previously reported `off' and low states (LS), we conclude that the `off' state is actually an extension of the LS, i.e. a LS at lower intensities. We propose that accretion models such as the advection-dominated accretion flows are able to explain the observed properties in such a state.

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A. K. H. Kong, E. Kuulkers, P. A. Charles, L. Homer. 2000-01-10. The Off State of GX 339-4. https://doi.org/10.1046/j.1365-8711.2000.03334.x

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