Fast infrared variability from a relativistic jet in GX 339--4

• Main Authors: Casella, P. (Author), Maccarone, T. .J (Author), O'Brien, K. (Author), Fender, R.P (Author), Russell, D.M (Author), van der Klis, M. (Author), Pe'er, A. (Author), Maitra, M. (Author), Altamirano, D. (Author), Belloni, T. (Author), Kanbach, G. (Author), Klien-Wolt, M. (Author), Mason, E. (Author), Soleri, P. (Author), Stefanescu, A. (Author), Wiersema, K. (Author), Wijnands, R. (Author)
• Format: Article
• Language: English
• Published: 2009-12-08.
• Subjects: Article
• Online Access: Get fulltext

 We present the discovery of fast infrared/X-ray correlated variability in the black-hole transient GX 339-4. The source was observed with sub-second time resolution simultaneously with VLT/ISAAC and RXTE/PCA in August 2008, 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 100 ms. The short time delay and the nearly symmetric cross-correlation function, together with the measured brightness temperature of 2.5 10⁶ K, 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.