Timing Properties of Active Galactic Nuclei
Smith, Evan Arnold
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Timing properties of Active Galactic Nuclei (AGN) are investigated primarily using archival data from the Rossi X-ray Timing Explorer (RXTE) satellite collected between 1996 and 2011. The main emphasis is to search for quasi-periodic oscillations (QPOs). This search was motivated by the uniqueness of the RXTE AGN database, which contains a gold-mine of information on the long-term light curves of AGN, as well as the fact that QPOs are a common feature in the light curves of stellar mass black hole (BH) and neutron star (NS) X-ray Binaries (XRBs).In stellar mass systems, QPOs have been used as strong diagnostics about the environment around the collapsed central object, and it is generally believed that super-massive (SM) BHs behave similarly, proportionally to their mass. To date, only a very few QPOs have been found in AGN light curves, with the RXTE AGN database having previously been almost completely unexplored. The few AGNQPOs detected to date have tended to be high frequency (HF). The RXTE AGN light curves offer a unique chance to find low-frequency (LF) QPOs at periods that could not be searched in other data sets. We searched 76 AGN from the RXTE archive and found 22 AGN with QPOs. Thus, we find that AGN LFQPOs not only exist, but are a common feature of AGN. We compare these results with similar phenomena in stellar-mass BH XRBs, finding that the LFQPO periods fit with the hypothesis of being modulated by Lense-Thirring precession, as has been suggested for some LFQPOs in XRBs. QPOs in x-ray binaries have been extensively studied and several models have been developed. Our timing analysis of RXTE AGN light curves uses the Lomb-Scargle periodogram, a techniques used for unevenly spaced data. We sometimes compare our RXTE Proportional Counter Array (PCA) results with results from other AGN observations, including the RXTE All-Sky Monitor (ASM) and Swift Burst Alert Telescope (BAT).