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M.W. Pakull (Obs. Strasbourg)
We present new optical observations of ultraluminous X-ray sources in nearby galaxies. Many of the non-obscured ULX are surrounded by large (several hundred parsec diameter) ionized nebulae with bubble-like morphology. Measured supersonic expansion velocities of 80 km/s or more imply formation either by exceedingly energetic supernova explosions, or by continuous inflation over the last 106 years by mildly relativistic jets like in the microquasar SS433 and its radio nebula W50. A census of similar bubbles not being associated with observable X-ray emission can provide important constraints on lifetime and beaming properties of ULX.
Optical counterparts of at least two ULX display the hallmark of X-ray binaries in the form of broad HeII \lambda4686 emission which is probably produced in an accretion disk. These detections open the route towards direct determination of the accretor's mass in ULX.
The author(s) of this abstract have provided an email address for comments about the abstract: pakull@astro.u-strasbg.fr
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Bulletin of the American Astronomical Society, 36 #2
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