Multi-Wavelength Observations of GX 339-4: First Spitzer Detection of a Black Hole Binary

Using multi-wavelength observations of Galactic black hole (BH) binaries, we can learn about the physical processes at work in these systems, including improving our understanding of emission mechanisms, accretion processes, and jet production. With the launch of the Spitzer Space Telescope, we have recently been able to extend our studies into the far-IR (24-70 microns) where strong emission can be seen from compact jets or the accretion disk. On 2004 August 20, we simultaneously observed the BH binary GX 339-4 at radio, far-IR, near-IR, optical, and X-ray energies, and we report on the results from these observations. Based on the X-ray properties, GX 339-4 had just entered the "Steep Power-Law" state at this time. A detection in the radio band indicates the presence of optically thin synchrotron emission from a jet. In addition, we measured a flux of 135 +/- 34 microJy at 24 microns, representing the first detection of a black hole binary with Spitzer. We model the broadband spectral energy distribution (SED) and discuss the physical implications.