University of Leicester
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Diffuse and discrete sources of galactic x-ray emission

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posted on 2014-12-15, 10:41 authored by Alex. Hands
Our Galaxy is a luminous X-ray source by virtue of its discrete X-ray source populations and various large-scale diffuse processes which produce the ultra-hot interstellar medium. This thesis presents an analysis of the properties of a variety of Galactic X-ray emitting components, based on data from the EPIC CCD cameras onboard ESA's XMM-NEWTON satellite observatory. In total 51 individual observations are analysed for which the combined exposure time is nearly 900 ks. X-ray spectra measured over a wide range in Galactic longitude and latitude are used to disentangle the different components of the diffuse soft X-ray background (SXRB). The SXRB is comprised primarily of a two-temperature Galactic halo, an unabsorbed local hot bubble (LHB) and, in certain directions, an extended plasma 'superbubble', all with temperatures in the range of 1-3 million K. Observations towards the Galactic Plane provide evidence that the LHB may be larger in extent than has previously been assumed, with some of the emission lying behind an absorption wall with a column density of NH ~ 3 x 1020 cm-2. The diffuse hard X-ray phenomenon known as the Galactic ridge is investigated at various locations both on and near to the Galactic Plane. The spectrum of the ridge at high energies is well described by a thermal plasma model with a temperature of 108.0 K. The exact nature of this emission is uncertain but several possibilities are discussed in this thesis. The surface brightness of the ridge is measured as ~ 10-10 erg s -1 cm-2 deg-2 (2-10 keV), of which ~ 15% is due to point sources and a further ~2% has been resolved and identified as extended supernova remnants and HII regions. In the region of XMM-NEWTON's X-ray Galactic Plane Survey (XGPS), a total of 424 discrete X-ray sources have been detected. Cumulative log N - log S distributions, including data from other satellites, illustrate how the dominating source population changes from Galactic X-ray binaries at high fluxes to extragalactic objects at fainter fluxes. However, an additional lower luminosity population, possibly associated with cataclysmic variables and RS CVns, appears to contribute significantly at intermediate X-ray fluxes.


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University of Leicester

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  • Doctoral

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  • PhD



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