# Combining timing characteristics with physical broadband spectral modelling of black hole X-ray binary GX~339$-$4

## TL;DR

This study models the broadband emission of GX~339$-$4 during multiple outbursts, revealing the dominant role of a hot corona in X-ray spectra and significant jet contributions, while linking jet properties to X-ray variability patterns.

## Contribution

It introduces a combined corona and jet model fitting multi-wavelength data, connecting spectral and timing properties of GX~339$-$4 with physical jet and corona characteristics.

## Key findings

- X-ray spectra are best fit by inverse Compton scattering in a hot corona.
- Jet base contributes up to 50% of the 3-100 keV flux via inverse Compton scattering.
- Jet properties correlate with the shape of the X-ray variability.

## Abstract

GX~339$-$4 is a black hole X-ray binary that is a key focus of accretion studies since it goes into outburst roughly every two-to-three years. Tracking of its radio, IR and X-ray flux during multiple outbursts reveals tight broadband correlations. The radio emission originates in a compact, self-absorbed jet, however the origin of the X-ray emission is still debated: jet base or corona? We fit 20 quasi-simultaneous radio, IR, optical and X-ray observations of GX~339$-$4 covering three separate outbursts in 2005, 2007, 2010--2011, with a composite corona + jet model, where inverse Compton emission from both regions contributes to the X-ray emission. Using a recently-proposed identifier of the X-ray variability properties known as power-spectral hue, we attempt to explain both the spectral and evolving timing characteristics, with the model. We find the X-ray spectra are best fit by inverse Compton scattering in a dominant hot corona ($kT_{\rm e}\sim$ hundreds of keV). However, radio and IR-optical constraints imply a non-negligible contribution from inverse Compton scattering off hotter electrons ($kT_{\rm e} \ge 511$~keV) in the base of the jets, ranging from a few up to $\sim50$\% of the integrated 3--100~keV flux. We also find that the physical properties of the jet show interesting correlations with the shape of the broadband X-ray variability of the source, posing intriguing suggestions for the connection between the jet and corona.