The first X-ray survey of Galactic luminous blue variables

Aims. The X-ray emission of massive stars has been studied when these objects are in their main-sequence phase, as well as when they are 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-Newton survey and archival XMM-Newton and Chandra observations, we performed the first X-ray survey of LBVs: about half of the known LBVs or candidate LBVs were 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[LX/LBOL] − 9.4 for P Cyg. This variety in the strength of the X-ray emission is discussed, with particular emphasis on the potential influence of binarity.

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