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arXiv · 1011.3295

Identification of a Population of X-ray Emitting Massive Stars in the Galactic Plane

G. E. Anderson·B. M. Gaensler·D. L. Kaplan·B. Posselt·P. O. Slane·S. S. Murray·J. C. Mauerhan·R. A. Benjamin·C. L. Brogan·D. Chakrabarty·J. J. Drake·J. E. Drew·J. E. Grindlay·J. Hong·T. J. W. Lazio·J. C. Lee·D. T. H. Steeghs·M. H. van Kerkwijk
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Abstract

We present X-ray, infrared, optical and radio observations of four previously unidentified Galactic plane X-ray sources, AX J163252-4746, AX J184738-0156, AX J144701-5919 and AX J144547-5931. Detection of each source with the Chandra X-ray Observatory has provided sub-arcsecond localizations, which we use to identify bright infrared counterparts to all four objects. Infrared and optical spectroscopy of these counterparts demonstrate that all four X-ray sources are extremely massive stars, with spectral classifications Ofpe/WN9 (AX J163252-4746), WN7 (AX J184738-0156 = WR121a), WN7-8h (AX J144701-5919) and OIf+ (AX J144547-5931). AX J163252-4746 and AX J184738-0156 are both luminous, hard, X-ray emitters with strong Fe XXV emission lines in their X-ray spectra at ~6.7 keV. The multi-wavelength properties of AX J163252-4746 and AX J184738-0156 are not consistent with isolated massive stars or accretion onto a compact companion; we conclude that their X-ray emission is most likely generated in a colliding-wind binary system. For both AX J144701-5919 and AX J144547-5931, the X-ray emission is an order of magnitude less luminous and with a softer spectrum. These properties are consistent with a colliding-wind binary interpretation for these two sources also, but other mechanisms for the generation of X-rays cannot be excluded. There are many other as yet unidentified X-ray sources in the Galactic plane, with X-ray properties similar to those seen for AX J163252-4746, AX J184738-0156, AX J144701-5919 and AX J144547-5931. This may indicate a substantial population of X-ray-emitting massive stars and colliding-wind binaries in the Milky Way.

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G. E. Anderson, B. M. Gaensler, D. L. Kaplan, B. Posselt, P. O. Slane, S. S. Murray, J. C. Mauerhan, R. A. Benjamin, C. L. Brogan, D. Chakrabarty, J. J. Drake, J. E. Drew, J. E. Grindlay, J. Hong, T. J. W. Lazio, J. C. Lee, D. T. H. Steeghs, M. H. van Kerkwijk. 2010-11-15. Identification of a Population of X-ray Emitting Massive Stars in the Galactic Plane. https://doi.org/10.1088/0004-637x%2F727%2F2%2F105

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