On the role of relativistic On the role of relativistic effects in the X-ray variability effects in the X-ray variability

of AGNof AGN

Piotr ŻyckiPiotr ŻyckiNicolaus Copernicus Astronomical Center, Warsaw, POLANDNicolaus Copernicus Astronomical Center, Warsaw, POLAND

Andrzej NiedźwieckiAndrzej NiedźwieckiŁódź University, Department of Physics, Łódź, POLANDŁódź University, Department of Physics, Łódź, POLAND

Relativistic effects in X-ray spectraRelativistic effects in X-ray spectra

Broad Iron Kα line observed in many sources: AGN, X-ray binaries (with black holes and neutron stars).

The line is broad because the accretion disk is rotating.

What if the X-ray source rotated?

Short-term effects of rotation of an X-ray sourceShort-term effects of rotation of an X-ray source

Modulation of the primary emission on the orbital time scale

Sun610 MM Życki & Niedźwiecki 2005

Quasi-periodic signal in power spectra expected…Quasi-periodic signal in power spectra expected…

Sun610 MM Życki & Niedźwiecki 2005

……but not seen in MCG—6-30-15but not seen in MCG—6-30-15

Vaughan et al. 2003

However, periodic modulation of the line However, periodic modulation of the line was observed in NGC 3516was observed in NGC 3516

Iwasawa,Miniutti & Fabian 2004

Can be modelled with a co-rotating flare model

Puzzling aspects of long-term (hours-days) Puzzling aspects of long-term (hours-days) X-ray variability of AGNX-ray variability of AGN

Variability of the reprocessing features (mainly the Fe Kα line) is weaker than, and uncorrelated with, the variability of the primary emission.

The light-bending modelThe light-bending model

ρ = 2 Rg

Assumptions:

Intrinsic source luminosity is constant.

Variability due to change of position of the source, and related change of strength of relativistic effects.

Variations of the observed flux and the flux seen by the disk are not correlated, because of relativistic effects.

Source averaged over the azimuthal angle (a ring really).

Miniutti & Fabian 2004

Line profilesLine profiles

Good fits to the observed line profiles are obtained for small height of the source

h=0.2-0.6 Rg h=8 Rg

(superposition)

( ρ = 2 Rg)

h≈0.07 r, r=2-3 Rg

i=30o

Line vs continuum variabilityLine vs continuum variability

Model with ρ=2, varying height (M&F)

Source just above the disk, changing radial position

Source close to the axis

Source just above the disk, changing radial position. Luminosity follows dissipation rate.

i=30o

So, the light-bending model So, the light-bending model for AGN for AGN ……

… can work, in the geometry of radial motion of X-ray sources, low above the disk.

The questions are: •How fundamental this is (does it apply to all source accreting at high Mdot?)•What is the physical mechanism?

High inclination sourcesHigh inclination sources

i=63o

Model with ρ=2, varying height (M&F)

Source just above the disk, changing radial position

Source close to the axis

The model works in broader range of parameters (height)