Colliding stellar wind modelling of the X-ray emission from WR 140

TL;DR

This study models X-ray emissions from the binary WR 140 using colliding stellar wind theory, revealing variable plasma emission and absorption effects near periastron, and highlighting the need for more complex wind models.

Contribution

It introduces models with partial electron heating that better fit X-ray data and discusses the impact of clumpy winds and non-spherical geometries on observations.

Findings

Partial electron heating models fit data better.

X-ray emission measure decreases near periastron.

Additional absorption observed near periastron.

Abstract

We modelled the Chandra and RXTE X-ray spectra of the massive binary WR 140 in the framework of the standard colliding stellar wind (CSW) picture. Models with partial electron heating at the shock fronts are a better representation of the X-ray data than those with complete temperature equalization. Emission measure of the X-ray plasma in the CSW region exhibits a considerable decrease at orbital phases near periastron. This is equivalent to variable effective mass-loss rates over the binary orbit. At orbital phases near periastron, a considerable X-ray absorption in excess to that from the stellar winds in WR 140 is present. The standard CSW model provides line profiles that in general do not match well the observed line profiles of the strong line features in the X-ray spectrum of WR 140. The variable effective mass-loss rate could be understood qualitatively in CSW picture of clumpy stellar winds where clumps are efficiently dissolved in the CSW region near apastron but not at periastron. However, future development of CSW models with non-spherically-symmetric stellar winds might be needed to get a better correspondence between theory and observations.