[Show abstract][Hide abstract] ABSTRACT: We present the discovery of fast infrared/X-ray correlated variability in the black hole transient GX 339−4. The source was
observed with subsecond time resolution simultaneously with Very Large Telescope/Infrared Spectrometer And Array Camera and
Rossi X-ray Timing Explorer/Proportional Counter Array in 2008 August, during its persistent low-flux highly variable hard state. The data show a strong
correlated variability, with the infrared emission lagging the X-ray emission by 100ms. The short time delay and the nearly
symmetric cross-correlation function, together with the measured brightness temperature of ∼2.5 × 106K, indicate that the bright and highly variable infrared emission most likely comes from a jet near the black hole. Under
standard assumptions about jet physics, the measured time delay can provide us a lower limit of Γ > 2 for the Lorentz factor
of the jet. This suggests that jets from stellar-mass black holes are at least mildly relativistic near their launching region.
We discuss implications for future applications of this technique.
Full-text · Article · Feb 2010 · Monthly Notices of the Royal Astronomical Society