# A different view of wind in X-ray binaries: The Accretion Disc Corona source 2S 0921-630

## TL;DR

This paper investigates the origin of accretion disc coronae in X-ray binaries, providing evidence that thermal-radiative winds driven by the central source explain observed spectral features, supported by simulations and high-resolution spectra.

## Contribution

It demonstrates that thermal-radiative winds can account for the wind emission lines in ADC sources, confirming their role in the structure of X-ray binaries.

## Key findings

- Model agrees with observed wind emission lines in 2S 0921-630
- Thermal-radiative winds are the likely origin of ADC
- High-resolution spectra can test wind models via blueshifted absorption lines

## Abstract

Accretion disc coronae (ADC) sources are very high inclination neutron star or black hole binaries, where the outer accretion flow blocks a direct view of the central source. The weak observed X-ray emission is instead produced mainly by scattering of the intrinsic radiation from highly ionised gas surrounding the source, the ADC. However, the origin of this scattering material is still under debate. We use the ADC source 2S 0921-630 (V395 Car) to test whether it is consistent with a thermal-radiative wind produced by the central X-ray source illuminating and puffing up the outer disc. This wind is clearly visible in blueshifted absorption lines in less highly inclined systems, where the source is seen directly through this material. Using the phenomenological photoionised plasma model, we first characterise the parameter that drives emission lines observed in 2S0921 in XMM-Newton and Chandra data. Following this, we run the Monte Carlo radiation transfer simulation to get scattered/reprocessed emissions in the wind, with the density and velocity structure obtained from the previous work. Our model agrees with all the wind emission lines in the Chandra high and medium energy grating spectra for an intrinsic source luminosity of L > 0.2 LEdd. This result strongly favours thermal-radiative winds as the origin of the ADC. We also show how high-resolution spectra via microcalorimeters can provide a definitive test by detecting blueshifted absorption lines.