Extragalactic X-ray binaries: black holes and neutron stars in Centaurus A

Burke, Mark J. (2013). Extragalactic X-ray binaries: black holes and neutron stars in Centaurus A. University of Birmingham. Ph.D.

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Abstract

This thesis presents research into the X-ray binary population of NGC 5128 (Centaurus A). The two principle investigations focus on the identification of black hole candidates, which can be identified by their long term variability and spectral properties. We demonstrate this with what we believe is our best example; a source that faded over two months of observations and displayed cool disc thermal-dominant spectra when at high luminosities- similar to the Galactic black hole X-ray binaries. The main result of this research is that the population of black hole X-ray binaries is more pronounced in the dust lane of the galaxy compared to in the halo. The explanation of this result, based around the mass of the donor stars required for systems to emit at the observed luminosities, may also explain the long noted effect of a steepening of the X-ray luminosity function in early-type galaxies at a few 10٨38 erg/s; an effect that increases with the age of the stellar population.

Finally, frequent Chandra observations of the NGC 5128 were used to investigate the two known ultraluminous
X-ray sources. These are transient systems and were observed at luminosities (1-10)% of their peak, in the regime frequented by the Galactic X-ray binaries. This presented an exciting opportunity to study the lower luminosity behaviour of these systems in an effort to determine the mass of the accreting compact object. The results of the spectral analysis point towards accretion powered by a stellar, rather than intermediate mass black hole. The long term variability of these sources is reminiscent of several of the long period Galactic X-ray binaries.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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