X-ray variability time scales in Active Galactic Nuclei

Abstract

X-ray variability in Active Galactic Nuclei (AGN) is commonly analysed in terms of the Power Spectral Density (PSD). The break observed in the power spectrum can be interpreted as a characteristic X-ray variability time scale. Here we study variability properties within the framework of clumpy accretion flows, in which shocks between accreting elements account for the UV and X-ray emissions. We derive a characteristic X-ray time scale, ${\tau }_X$, and compare it with the measured PSD break time scale, $T_B$. A quite good agreement is found in both magnitude and trend. In particular, the model dependence on black hole mass and accretion rate precisely reproduces the empirical relation obtained by McHardy et al. (2006). We suggest a possible physical interpretation of the break time scale and briefly discuss the related aspects of optical/UV variability and correlations between different wavelengths.

6 pages, 1 figure, accepted for publication in Astronomy and Astrophysics

References in corpus (4)

• The multiwavelength variability of 3C 273
• Correlated X-ray/Optical Variability in the Quasar MR2251-178
• Correlated X-ray and Optical Variability in Mkn 509
• AGN's UV and X-ray luminosities in clumpy accretion flows

Cited by in corpus (11)

• X-ray power law spectra in active galactic nuclei
• A transient radio source consistent with a merger-triggered core collapse supernova
• The First Hard X-Ray Power Spectral Density Functions of AGN
• Synchrotron radio emission in radio-quiet AGNs
• The physical origin of the X-ray power spectral density break timescale in accreting black holes
• BASS-XL: X-ray variability properties of unobscured Active Galactic Nuclei
• The catalog of variable sources detected by INTEGRAL I: Catalog and Techniques
• Characterisation of the X-ray point source variability in the eROSITA south ecliptic pole field
• Disk evolution of the M87's nucleus observed in 2008
• AGN variability in the age of VRO
• Intra-day variability of three Seyfert Galaxies measured with XMM-Newton