X-Ray Variability and the Inner Region in Active Galactic Nuclei
Abstract
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 Fvar\propto M-0.4\bullet . 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 2.85 × 107 M ⊙ in NGC 4051, 8.02 × 107 M ⊙ in MRK 766, and 4.68 × 107 M ⊙ 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 <~ 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 6.3 × 10-2 to 4.25 × 106, containing the observed Q. The derived value of Q ~ 32 for REJ 1034+396 therefore suggests that the AGN hosts a thin disk.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2014
- DOI:
- 10.1088/0004-637X/791/2/74
- arXiv:
- arXiv:1406.6469
- Bibcode:
- 2014ApJ...791...74M
- Keywords:
-
- accretion;
- accretion disks;
- black hole physics;
- galaxies: active;
- galaxies: Seyfert;
- methods: statistical;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 32 pages, 11 figures (9 sub-figures)