Unifying disc-jet behaviour in X-ray binaries: an optical/IR approach

TL;DR

This paper demonstrates that optical/IR colour-magnitude diagrams effectively distinguish thermal disc emission from non-thermal jet emission in X-ray binaries, enabling predictions of multi-wavelength properties from optical/IR data.

Contribution

It introduces a unified optical/IR approach to understanding disc-jet behaviour in X-ray binaries, linking optical/IR observations with X-ray and radio states.

Findings

Optical/IR diagrams separate thermal and non-thermal emission.

A blackbody model reproduces observed colour-magnitude relations.

Predictions of X-ray and radio properties from optical/IR data are possible.

Abstract

Synchrotron emission from jets produced by X-ray binaries can be detected at optical and infrared (IR) frequencies. I show that optical/IR colour-magnitude diagrams of the outbursts of nine X-ray binaries successfully separate thermal disc emission from non-thermal jet emission, in both black hole and neutron star sources. A heated single-temperature blackbody is able to reproduce the observed relations between colour and magnitude, except when excursions are made to a redder colour than expected, which is due to jet emission. The general picture that is developed is then incorporated into the unified picture of disc-jet behaviour in black hole X-ray binaries. At a given position of a source in the X-ray hardness-intensity diagram, the radio, IR and optical properties can be inferred. Similarly, it is possible to predict the X-ray and radio luminosities and spectral states from optical/IR monitoring.