X-RAY VARIABILITY AND THE INNER REGION IN ACTIVE GALACTIC NUCLEI

We present theoretical models of X-ray variability attributable to orbital signatures from an accretion disk including emission region size, quasi-periodic oscillations (QPOs), and its quality factor Q, and the emergence of a break frequency in the power spectral density shape. We find a fractional variability amplitude of F-var alpha M-0.4. We conduct a time series analysis on X-ray light curves (0.3-10 keV) of a sample of active galactic nuclei (AGNs). A statistically significant bend frequency is inferred in 9 of 58 light curves (16%) from 3 AGNs for which the break timescale is consistent with the reported BH spin but not with the reported BH mass. Upper limits of 2.85x10(7)M in NGC 4051, 8.02x10(7)M circle dot in MRK766, and 4.68x10(7)M circle dot in MCG-6-30-15 are inferred for maximally spinning BHs. For REJ 1034+396 where a QPO at 3733 s was reported, we obtain an emission region size of (6-6.5) M and a BH spin of a less than or similar to 0.08. The relativistic inner region of a thin disk, dominated by radiation pressure and electron scattering, is likely to host the orbital features as the simulated Q ranges from 6.3x10(-2) to 4.25x10(6), containing the observed Q. The derived value of Q similar to 32 for REJ 1034+396 therefore suggests that the AGN hosts a thin disk.