The XMM-Newton EPIC X-ray Light Curve Analysis of WR 6

TL;DR

This study analyzes X-ray variability in Wolf-Rayet star WR 6 using XMM-Newton data, finding no clear cyclic pattern but proposing a co-rotating interaction region model to explain the observed X-ray behavior.

Contribution

It introduces a phenomenological CIR model to explain X-ray variability in WR 6, supported by high-quality observational data and spectral analysis.

Findings

No cyclic behavior detected in phased light curves.

No event clustering observed in photon arrival times.

CIR model can potentially explain X-ray variability.

Abstract

We obtained four pointings of over 100 ks each of the well-studied Wolf-Rayet star WR 6 with the XMM-Newton satellite. With a first paper emphasizing the results of spectral analysis, this follow-up highlights the X-ray variability clearly detected in all four pointings. However, phased light curves fail to confirm obvious cyclic behavior on the well-established 3.766 d period widely found at longer wavelengths. The data are of such quality that we were able to conduct a search for "event clustering" in the arrival times of X-ray photons. However, we fail to detect any such clustering. One possibility is that X-rays are generated in a stationary shock structure. In this context we favor a co-rotating interaction region (CIR) and present a phenomenological model for X-rays from a CIR structure. We show that a CIR has the potential to account simultaneously for the X-ray variability and constraints provided by the spectral analysis. Ultimately, the viability of the CIR model will require both intermittent long-term X-ray monitoring of WR 6 and better physical models of CIR X-ray production at large radii in stellar winds.