The Off State of GX 339 – 4
نویسنده
چکیده
We report BeppoSAX and optical observations of the black hole candidate GX339– 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 6.6 × 10 erg s 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 4U1630–47. 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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