Interpreting the X-ray state transitions of Cygnus X-1

TL;DR

This paper introduces a new method combining spectroscopic data and radiation hydrodynamic models to interpret X-ray state transitions in Cygnus X-1, showing how X-ray intensity affects circumstellar medium and Doppler tomograms.

Contribution

It develops a novel approach integrating models and observations to understand state transitions in high-mass X-ray binaries.

Findings

Synthetic Doppler tomograms match observed data.

X-ray intensity changes cause significant circumstellar medium redistribution.

State transitions are reflected in observable spectral features.

Abstract

We present a novel method for interpreting observations of high-mass X-ray binaries (HMXBs) based on a combination of spectroscopic data and numerical results from a radiation hydrodynamic model of stellar winds. We calculate synthetic Doppler tomograms of predicted emission in low/hard and high/soft X-ray states and compare them with Doppler tomograms produced using spectra of Cygnus X-1, a prototype of HMXBs. Emission from HMXBs is determined by local conditions within the circumstellar medium, namely density, temperature, and ionization state. These quantities depend strongly on the X-ray state of the systems. By increasing intensity of an X-ray emission produced by the compact companion in the HMXB model, we achieved a complete redistribution of the circumstellar medium in the vicinity of the modelled system. These changes (which simulate the transitions between two major spectral states) are also apparent in the synthetic Doppler tomograms which are in good agreement with the observations.