Open AccessThe ‘off’ state of GX 339–4
Author(s) -
Kong A. K. H.,
Kuulkers E.,
Charles P. A.,
Homer L.
Publication year - 2000
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2000.03334.x
Subject(s) - physics , astrophysics , accretion (finance) , flux (metallurgy) , luminosity , black hole (networking) , power law , spectral index , accretion disc , wavelength , spectral line , light curve , astronomy , optics , galaxy , computer network , routing protocol , statistics , materials science , routing (electronic design automation) , mathematics , computer science , metallurgy , link state routing protocol
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 6.6×10 33 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. 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.