# Photoionization Emission Models for the Cyg X-3 X-ray Spectrum

## TL;DR

This paper models the X-ray emission spectrum of Cyg X-3, revealing a dense wind likely from the companion star, and distinguishes different emission regions through spectral line analysis.

## Contribution

It introduces a detailed photoionization model for Cyg X-3's X-ray spectrum, highlighting the wind's properties and the distinct origins of emission lines.

## Key findings

- Density of emission region ≥ 10^12 cm^-3
- Wind features prominent in lighter element lines
- Iron K lines originate from a different region

## Abstract

We present model fits to the X-ray line spectrum of the well known High Mass X-ray binary Cyg X-3. The primary observational dataset is a spectrum taken with the $Chandra$ X-ray Observatory High Energy Transmission Grating (HETG) in 2006, though we compare it to all the other observations of this source taken so far by this instrument. We show that the density must be $\geq 10^{12}$ cm$^{-3}$ in the region responsible for most of the emission. We discuss the influence of the dust scattering halo on the broad band spectrum and we argue that dust scattering and extinction is not the most likely origin for the narrow featureseen near the Si K edge. We identify the features of a wind in the profiles of the strong resonance lines and we show that the wind is more apparent in the lines from the lighter elements. We argue that this wind is most likely associated with the companion star. We show that the intensities of most lines can be fitted, crudely, by a single component photoionized model. However, the iron K lines do not fit with this model. We show that the iron K line variability as a function of orbital phase is different from the lower energy lines, which indicates that the lines arise in physically distinct regions. We discuss the interpretation of these results in the context of what is known about the system and similar sys