The first X-ray survey of Galactic Luminous Blue Variables

TL;DR

This paper presents the first X-ray survey of Galactic Luminous Blue Variables, revealing diverse X-ray emission properties and exploring their potential links to binarity, filling a key gap in understanding their high-energy behavior.

Contribution

It provides the first systematic X-ray observations of LBVs, identifying known and new X-ray sources and setting upper limits for non-detections, thus advancing knowledge of their high-energy characteristics.

Findings

Detected four LBVs in X-ray, including eta Car and Cyg OB2 #12.

Upper limits on X-ray flux for undetected LBVs, e.g., P Cygni.

Discussed the role of binarity in X-ray emission variability.

Abstract

Aims: The X-ray emission of massive stars has been studied when these objects are in their main-sequence phase, as well as in their Wolf-Rayet phase. However, the X-ray properties of the transitional Luminous Blue Variable (LBV) phase remain unknown. Methods: Using a dedicated but limited XMM survey as well as archival XMM and Chandra observations, we performed the first X-ray survey of LBVs: about half of the known LBVs or candidate LBVs are studied. Results: Apart from the well known X-ray sources eta Car and Cyg OB2 #12, four additional LBVs are detected in this survey, though some doubt remains on the association with the X-ray source for two of these. For the other LBVs, upper limits on the flux were derived, down to $\log[L_{\rm X}/L_{\rm BOL}]-9.4$ for PCyg. This variety in the strength of the X-ray emission is discussed, with particular emphasis on the potential influence of binarity.