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

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

• Piotr Zycki
• Nicolaus Copernicus Astronomical Center, Warsaw,
  POLAND
• Andrzej Niedzwiecki
• Lódz University, Department of Physics, Lódz,
  POLAND

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Relativistic effects in X-ray spectra
Broad Iron Ka 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?
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Short-term effects of rotation of an X-ray source
Modulation of the primary emission on the orbital
time scale
Zycki Niedzwiecki 2005
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Quasi-periodic signal in power spectra expected
Zycki Niedzwiecki 2005
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but not seen in MCG6-30-15
Vaughan et al. 2003
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However, periodic modulation of the line was
observed in NGC 3516
Iwasawa,Miniutti Fabian 2004
Can be modelled with a co-rotating flare model
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Puzzling aspects of long-term (hours-days) X-ray
variability of AGN
Variability of the reprocessing features (mainly
the Fe Ka line) is weaker than, and uncorrelated
with, the variability of the primary emission.
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The light-bending model
Miniutti Fabian 2004
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).
? 2 Rg
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Line profiles
i30o
h0.2-0.6 Rg h8 Rg
(superposition)
( ? 2 Rg)
h0.07 r, r2-3 Rg
Good fits to the observed line profiles are
obtained for small height of the source
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Line vs continuum variability
i30o
Model with ?2, varying height (MF) 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.
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So, the light-bending model 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?

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High inclination sources
i63o
Model with ?2, varying height (MF) Source just
above the disk, changing radial position Source
close to the axis
The model works in broader range of parameters
(height)