Physics
Scientific paper
Jun 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt........32d&link_type=abstract
PhD Thesis, Paris VII University (1998)
Physics
1
Accretion, Accretion Discs, Instabilities, Binaries: Close, Cataclysmic Variables, Galaxies: Individual Messier Number: M33, Galaxies: Local Group, Galaxies: Nuclei, X-Rays: Stars
Scientific paper
This PhD thesis presents X-ray observations of the nearby galaxy M33 and an X-ray irradiated accretion disk model. X-ray observations of nearby galaxies allow direct access to the underlying high energy populations, amongst which are X-ray binaries where a compact object (black hole, neutron star) accretes matter from its normal star companion. I present a catalogue and a variability analysis of the sources in M33 detected by the X-ray satellite ROSAT. I discuss X-7 which is shown to be an X-ray binary pulsar. Some 70% of the X-ray flux from M33 comes from the nucleus source X-8. I show that the luminosity from this object is modulated on a 106 day period. Additional observations obtained with the Hubble Space Telescope show a bright stellar-like UV source in the center of the nucleus. These observations significantly constrain models of the bright (Lx~1e39 ergs/s) nucleus source which we believe to be a 10 solar mass black hole X-ray binary. Illumination of the accretion disk surrounding the compact object plays a crucial role in such a system. An accretion disk is thermally and viscously unstable around the hydrogen ionisation temperature. This instability is thought to power the outbursts of dwarf novae and soft X-ray transients. I present a numerical code that can follow the evolution of the instability in a disk with high precision. This model is modified to account for illumination. Contrary to observations of low mass X-ray binaries, illumination by a point source does not modify the properties of a planar disk. However, if the illumination source is not in the disk plane, as is the case for instance if the disk is warped or if the source is above the disk, illumination can stabilise the disk. It is concluded that the physical processes and the geometry of illumination in low mass X-ray binaries is still ill-understood.
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