Chandra revisits WR48a: testing colliding wind models in massive binaries

TL;DR

This study uses new and archival Chandra and XMM-Newton X-ray data to analyze the colliding wind binary WR 48a, revealing spectral line broadening, variability in X-ray emission and absorption, and supporting the colliding stellar wind model.

Contribution

The paper provides detailed high-resolution spectral analysis of WR 48a, confirming the colliding stellar wind model and demonstrating long-term variability in X-ray emission and absorption.

Findings

Spectral lines are broadened and slightly blueshifted.

X-ray emission and absorption vary over years.

Clumpy stellar winds may influence observed variability.

Abstract

We present results of new Chandra High-Energy Transmission Grating (HETG) observations (2019 November - December) of the massive Wolf-Rayet (WR) binary WR 48a. Analysis of these high-quality data showed that the spectral lines in this massive binary are broadened (FWHM = 1400 km/s) and marginally blushifted (~ -100 km/s). A direct modelling of these high-resolution spectra in the framework of the standard colliding stellar wind (CSW) picture provided a very good correspondence between the shape of the theoretical and observed spectra. Also, the theoretical line profiles are in most cases an acceptable representation of the observed ones. We applied the CSW model to the X-ray spectra of WR 48a from previous observations: Chandra-HETG (2012 October) and XMM-Newton (2008 January). From this expanded analysis, we find that the observed X-ray emission from WR48a is variable on the long timescale (years) and the same is valid for its intrinsic X-ray emission. This requires variable mass-loss rates over the binary orbital period. The X-ray absorption (in excess of that from the stellar winds in the binary) is variable as well. We note that lower intrinsic X-ray emission is accompanied by higher X-ray absorption. A qualitative explanation could be that the presence of clumpy and non-spherically symmetric stellar winds may play a role.