X-ray spectroscopy and variability of the luminous quasar PDS 456
In this thesis I present contemporary X-ray observations of the “Rosetta Stone” of black hole winds, the luminous quasar PDS 456. I perform a detailed analysis of a recent, long Suzaku campaign in 2013 (of ~ 1 Ms duration) where the X-ray flux was unusually low. During this campaign PDS 456 displays significant short-term X-ray spectral variability, on time-scales of ~ 100 ks, due to variable absorbing gas crossing the line-of-sight. By investigating the physical properties of these X-ray absorbers I find that they constitute the same inhomogeneous ultra fast accretion disc-wind (vw ~ 0:25c), which is characterized by highly ionized gas, relatively close to the SMBH and colder, denser clumpy material located further out.
A series of five simultaneous observations of PDS 456 with XMM-Newton & NuSTAR then resolved the P-Cygni like profile at Fe K, confirming that the absorption originates from a fast (vmax = 0:35+_0:02c), wide angle (i.e., & 2p) wind, capable of causing significant feedback between the black hole and its host galaxy. Collating all the Suzaku and XMM-Newton & NuSTAR observations from 2007–2014, I show that the wind velocity appears correlated with the X-ray luminosity, which may imply that the wind is radiatively driven.
The last part of the project is focused on the broadband analysis of PDS456 from the 2007 archival Suzaku data (~ 370 ks in duration), where the quasar was observed in a high-flux state and the unabsorbed AGN primary continuum was revealed. Significant spectral variability is present during the intrinsic X-ray flares that are present in this observation, which are likely driven by fluctuations in a two-component (accretion disc plus corona) continuum. This takes the form of a variable soft X-ray excess (< 1 keV), likely to be the Comptonized tail of the accretion disc emission, as well as a high energy powerlaw. The X-ray emission in PDS 456 appears to originate from two distinct regions:- (i) a warm, optically thick layer of gas blanketing the disc, which is responsible for the soft X-ray excess and (ii) a hot/thin electron corona above the disc, which produces the hard X-ray emission. The latter is typically 10Rg in extent and appears to be Compton cooled by soft X-ray emission.
|Jan 1, 2017