Formation of the compact jets in the black hole GX 339-4

TL;DR

This study reports the first detection of variable far-infrared emission from the compact jets of black hole GX 339-4 during its outburst decay, revealing the evolution of jet emission across multiple wavelengths.

Contribution

It provides the first multi-wavelength observation of jet re-ignition in a black hole binary, including Herschel far-infrared data, showing the spectral evolution from radio to optical.

Findings

Detection of variable far-infrared emission from jets

Observation of jet re-ignition across radio, infrared, optical, and X-ray

Complex spectral energy distribution from radio to optical

Abstract

Galactic black hole binaries produce powerful outflows with emit over almost the entire electromagnetic spectrum. Here, we report the first detection with the Herschel observatory of a variable far-infrared source associated with the compact jets of the black hole transient GX 339-4 during the decay of its recent 2010-2011 outburst, after the transition to the hard state. We also outline the results of very sensitive radio observations conducted with the Australia Telescope Compact Array, along with a series of near-infrared, optical (OIR) and X-ray observations, allowing for the first time the re-ignition of the compact jets to be observed over a wide range of wavelengths. The compact jets first turn on at radio frequencies with an optically thin spectrum that later evolves to optically thick synchrotron emission. An OIR reflare is observed about ten days after the onset of radio and hard X-ray emission, likely reflecting the necessary time to build up enough density, as well as to have acceleration (e.g. through shocks) along an extended region in the jets. The Herschel measurements are consistent with an extrapolation of the radio inverted power-law spectrum, but they highlight a more complex radio to OIR spectral energy distribution for the jets.