Type of Document Dissertation Author Marshall, Kevin Author's Email Address marshall@chara.gsu.edu URN etd-12012006-141444 Title The X-ray Variability of Seyfert Galaxies Degree Ph.D. Department Physics and Astronomy Advisory Committee
Advisor Name Title H. Richard Miller Committee Chair D. Michael Crenshaw Committee Member Paul J. Wiita Committee Member Todd J. Henry Committee Member William H. Nelson Committee Member Keywords
- astronomy
- active galaxies
- X-rays
Date of Defense 2006-11-17 Availability unrestricted Abstract Strong and variable X-ray emission has long been known to be a universalproperty of active galaxies. However, despite years of study, the exact nature
of the variability remains relatively unknown. We present here results of
a multi-year monitoring campaign of a sample of Seyfert galaxies (3C 120,
Mkn 509, 3C 390.3, and Akn 120), carried out using the Rossi X-ray Timing
Explorer (RXTE). For Mkn 509, we also present results of optical monitoring.
Mkn 509 shows a strong correlation between X-ray and optical variations, with
the optical leading the X-ray by 25 days. We also investigate the rms-flux
relationship in our sample. The two radio loud objects in our sample
(3C 120, 3C 390.3) show a clear correlation between flux and rms variability,
while the two radio quiet objects (Mkn 509, Akn 120) show no such relationship.
Monte Carlo simulations were used to estimate the shape of the underlying
power spectrum, and we find that all of our objects have a break frequency
below which the power spectrum flattens. The relationship between optical and
X-ray variability is discussed, with lags occurring most likely as a result of
instabilities or changes in accretion flow propagating inwards through the
disk. We also discuss possible physical timescales that could be related to
the break frequency, along with connections to galactic X-ray binaries.
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