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Title: X-ray power spectral densities of active galactic nuclei
Author: Summons, Daniel Paul
ISNI:       0000 0001 3489 8865
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2007
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I address the question'of whether active galactic nuclei (AGN) exhibit similar Xray 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 progranunes 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 ai, -(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 data 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. The PSD and lag spectrum of Ark 564 strongly suggests that a two-component Lorentzian interpretation of the origin of most of the variability is correct. Given the super-EddiPgton accretion rate of Ark 564 it is most likely analogous to a very-high state system. These results further confinn the connection between AGN and BHXRBs. I use proprietary X-ray data from our RXTE monitoring progranune, together with other data from the RXTE archive and complementary data from XMM-Newton, ASCA, and EXOSAT to produce broadband PSDs for 32 AGN spanning the frequency range from rv 10-8 to rv 10-3 Hz. The X-ray data for each AGN are reduced and analysed in a consistent manner. In particular, to ensure consistency between different RXTE gain epochs, all RXTE monitoring data is calibrated with respect to public archival Crab PCA data. I apply PSRESP to the resulting PSDs to determine the undistorted shape. All of the 32 AGN are consistent with either an unbroken or single-bend power-law interpretation of their PSDs, with the exception of Ark 564. I thus show that, for an expanded sample, AGN do behave like scaled-up BHXRBs, with the bend timescale scaling as mass divided by accretion rate. Thus, I further endorse the result of McHardy et al. (2006).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available