The New X‐Ray Transient SAX J1711.6−3808: Decoupling between Its 3–20 keV Luminosity and Its State Transitions

We present a study of the correlated spectral and timing behavior of the newX-ray transient SAX J1711.6-3808 during its 2001 outburst using data obtainedwith the RXTE. We also investigate the correlations between those sourceproperties and the 3-20 keV X-ray luminosity. The behavior of the source duringthe observations can be divided into two distinct state types. During the hardstate, the energy spectra are relatively hard and can be described by only apower-law component, and the characteristic frequencies (i.e., the frequency ofthe 1-7 Hz QPOs observed for the first time in this source) in the powerspectra are low. However, during the ``soft'' state, the spectra areconsiderably softer (in addition to the power-law component, a soft componentis necessary to fit the spectra) and the frequencies are the highest observed.Remarkably, this distinction into two separate states cannot be extrapolated toalso include the 3-20 keV X-ray luminosity. Except for one observation, thisluminosity steadily decreased but the hard state was observed both at thehighest and lowest observed luminosities. In contrast, the soft state occurredonly at intermediate luminosities. This clearly demonstrates that the statebehavior of SAX J1711.6-3808 is decoupled from its X-ray luminosity and that ifthe X-ray luminosity traces the accretion rate in SAX J1711.6-3808, then thestate transitions are not good accretion rate indicators, or vice versa. Thedata of SAX J1711.6-3808 does not allow us to conclusively determine its exactnature. The source resembles both neutron star and black hole systems when theyhave low luminosities. We discuss our results with respect to the correlatedtiming and spectral behavior observed in other LMXBs and the implications ofour results on the modeling of the outburst light curves of X-ray transients.Comment: Accepted for publication in ApJ Main Journal, 13 September 200