SCYON Abstract

Received on June 7 2001

A dozen colliding wind X-ray binaries in the star cluster R136 in the 30 Doradus region

AuthorsSimon Portegies Zwart, David Pooley, Walter Lewin
Submitted toAstrophysical Journal


We analyzed archival Chandra X-ray observations of the central portion of the 30 Doradus region in the Large Magellanic Cloud. The image contains 20 X-ray point sources with luminosities between 5x1032 and 2x1035 erg/s (0.2 to 3.5 keV). A dozen sources have bright WN Wolf-Rayet or spectral type O stars as optical counterparts. Nine of these are within about 3.4 pc of R136, the central star cluster of NGC 2070. We derive an empirical relation between the X-ray luminosity and the parameters for the stellar wind of the optical counterpart. The relation gives good agreement for known colliding wind binaries in the Milky Way Galaxy and for the identified X-ray sources in NGC 2070. We conclude that probably all identified X-ray sources in NGC 2070 are colliding wind binaries and that they are not associated with compact objects. This conclusion contradicts Wang (1995) who argued, using ROSAT data, that two earlier discovered X-ray sources are accreting black-hole binaries. Five early type stars in R136 are not bright in X-rays, possibly indicating that they are either: single stars or have a low mass companion or a wide orbit. The resulting binary fraction among early type stars is unusually high; possibly all early type stars in the 30 Doradus region are binaries.