X-ray power spectral densities of active galactic nuclei

Summons, Daniel Paul (2007) X-ray power spectral densities of active galactic nuclei. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

I address the question of whether active galactic nuclei (AGN) exhibit similar X-ray temporal variability properties to black hole X-ray binaries (BHXRBs). I utilise long time-scale X-ray monitoring data to produce broadband power spectral densities (PSDs) for a variety of AGN. Unfortunately X-ray monitoring programmes of AGN often produce light curves that are irregularly sampled, which causes the observed PSD to become distorted. I therefore further developed a Monte Carlo modelling technique (PSRESP), based upon Uttley et al. (2002), to determine the undistorted broadband PSD and associate a robust acceptance probability to the fitted model. Using archival and proprietary Rossi X-ray Timing Explorer (RXTE) data, along with X-ray from XMM-Newton, I apply PSRESP to determine the undistorted PSD of NGC 3783, which had previously been suggested to be analogous to a ‘hard’ state BHXRB. I show that a second break is not statistically supported, and I show that this PSD is, in fact, well fitted by a ‘soft’ state model that has only one break at higher frequencies. These results leave Arakelian 564 as the only AGN which shows a second break at low frequencies. I present a power spectral analysis of a 100 ksec XMM-Newton observation along with RXTE and ASCA data of the narrow line Seyfert 1 galaxy Ark 564. I demonstrate that the PSD of Ark 564 is well fit by the sum of two Lorentzian-shaped components, similar to those seen in BHXRBs.