Internal shocks driven by accretion flow variability in the compact jet of the black hole binary GX 339-4

TL;DR

This study models the compact jet in the black hole binary GX 339-4 using internal shocks driven by accretion flow variability, successfully reproducing observed spectral energy distribution and variability in radio to infrared bands.

Contribution

It introduces a model linking jet variability to accretion flow fluctuations, explaining spectral and variability features in GX 339-4's jet emission.

Findings

Model reproduces the radio to infrared SED of GX 339-4.

Successfully explains the mid-infrared spectral variability.

Links jet fluctuations to X-ray variability of the accretion flow.

Abstract

In recent years, compact jets have been playing a growing role in the understanding of accreting black hole engines. In the case of X-ray binary systems, compact jets are usually associated with the hard state phase of a source outburst. Recent observations of GX 339-4 have demonstrated the presence of a variable synchrotron spectral break in the mid-infrared band that was associated with its compact jet. In the model used in this study, we assume that the jet emission is produced by electrons accelerated in internal shocks driven by rapid fluctuations of the jet velocity. The resulting spectral energy distribution (SED) and variability properties are very sensitive to the Fourier power spectrum density (PSD) of the assumed fluctuations of the jet Lorentz factor. These fluctuations are likely to be triggered by the variability of the accretion flow which is best traced by the X-ray emission. Taking the PSD of the jet Lorentz factor fluctuations to be identical to the observed X-ray PSD, our study finds that the internal shock model successfully reproduces the radio to infrared SED of the source at the time of the observations as well as the reported strong mid-infrared spectral variability.