Mehdipour, M; (2012) Ionised outflows and multi-wavelength variability of Active Galactic Nuclei. Doctoral thesis (PhD), UCL (University College London).

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Abstract

This thesis presents a study of ionised outflows and multi-wavelength variability of Active Galactic Nuclei (AGN) focusing on three Seyfert-type objects: NGC 3516, Mrk 509 and ESO 113-G010. For this work I have made use of mostly XMM-Newton data, i.e. high-resolution X-ray spectra from the Reflection Grating Spectrometer (RGS) for exploring the ionised outflows, and simultaneous optical/UV/X-ray data from the Optical Monitor (OM) and the European Photon Imaging Camera (EPIC) instruments to study the intrinsic emission and variability. I have investigated the structure and geometry of the partial-covering multi-phase ionised absorber of NGC 3516. I demonstrate that the X-ray variability, originally attributed to occultation by a cloud in an accretion disc wind passing in front of the source, is rather the result of changes in the intrinsic emission of the source. From a 100-day multi-wavelength campaign on Mrk 509, I find that the character of its variability, strictly correlated in the UV and soft X-ray bands, indicates that the soft X-ray excess emission is produced by Compton reprocessing of the UV disc emission in a warm corona encasing the inner disc. I have also studied the nuclear obscuration and the role of dust in the warm absorber of ESO 113-G010. I show that the cause of significant optical/UV reddening, despite the lack of X-ray absorption from neutral gas, is most likely to be dust embedded in a weakly-ionised phase of an absorber which is conspicuous in the high-resolution X-ray spectrum of this object. I have explored the uncertainties in the irradiating spectral energy distribution due to the nuclear obscuration of the source and the effects these have on the survival of the dust, on the thermal stability of the warm absorber phases and the ionisation balance calculations required for photoionisation modelling. From my case-studies of these three objects emerges a more detailed picture of the ionised outflows phenomenon and of the environment in the vicinity of the nuclear supermassive black holes in AGN.

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