2000MNRAS.312L..49K

We report BeppoSAX and optical observations of the black hole candidate GX339-4 during its X-ray `off' state in 1999. The broad-band (0.8-50keV) X-ray emission can be fitted by a single power law with spectral index, α∼1.6. The observed luminosity is 6.6x10<sup>33</sup>erg.s<sup>–1</sup> in the 0.5-10keV 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 GS2023+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. an 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.