Effects of the stellar wind on X-ray spectra of Cygnus X-3

TL;DR

This study models the X-ray spectra of Cygnus X-3 considering stellar wind effects, revealing a two-phase wind structure and suggesting the compact object is likely a black hole.

Contribution

It introduces a detailed model of the stellar wind's impact on X-ray spectra, including a two-phase wind structure and implications for the nature of the compact object.

Findings

The wind consists of a hot plasma and small dense cool clumps.

The mass-loss rate is estimated at (0.6--1.6) x 10^-5 solar masses per year.

A continuum model dominated by Compton reflection best fits the data.

Abstract

We study X-ray spectra of Cyg X-3 from BeppoSAX, taking into account absorption and emission in the strong stellar wind of its companion. We find the intrinsic X-ray spectra are well modelled by disc blackbody emission, its upscattering by hot electrons with a hybrid distribution, and by Compton reflection. These spectra are strongly modified by absorption and reprocessing in the stellar wind, which we model using the photoionization code cloudy. The form of the observed spectra implies the wind is composed of two phases. A hot tenuous plasma containing most of the wind mass is required to account for the observed features of very strongly ionized Fe. Small dense cool clumps filling <0.01 of the volume are required to absorb the soft X-ray excess, which is emitted by the hot phase but not present in the data. The total mass-loss rate is found to be (0.6--1.6) x 10^-5 solar masses per year. We also discuss the feasibility of the continuum model dominated by Compton reflection, which we find to best describe our data. The intrinsic luminosities of our models suggest that the compact object is a black hole.