The Off State of GX 339-4
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, \alpha ~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.
Keywords
Cite
@article{arxiv.astro-ph/0001158,
title = {The Off State of GX 339-4},
author = {A. K. H. Kong and E. Kuulkers and P. A. Charles and L. Homer},
journal= {arXiv preprint arXiv:astro-ph/0001158},
year = {2009}
}
Comments
Accepted for publication in MNRAS