variability of radio-quiet agn across the spectrum: facts and ideas b. czerny copernicus...
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Variability of radio-quiet AGN across the
spectrum: facts and ideasB. Czerny
Copernicus Astronomical Center, Warsaw, Poland
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Outline
• Flow geometry• Basic timescales in alpha disks• Basic instabilities in alpha disks• Nature of viscosity, instabilities in MHD
simulations• Disk – hot medium interaction and its effect
on the time variability • Hot medium origin
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Flow geometry
High L/LEdd – disk approaching black hole, spectra disk-dominated
Low L/LEdd – disk retreating, spectra dominated by hot thermal plasma
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Flow geometry
An example of disk-dominated spectrum: WLQ SDSS J094533.99+100950.1
(Hryniewicz et al., in preparation)
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Basic timescales in alpha disksViscous torque = alpha*Ptot
Orbital motion
Optical variability ?
Evolution of surface density
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Basic instabilities in alpha disks
• Radiation pressure instability (inner disk)• Ionization instability (middle disk)• Gravitational instability (outer disk)
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Radiation pressure instabilityGRS 1915+105 is the only galactic source showing (occasionally) this instability.
example of GRS 1915+105 lightcurve from Belloni et al. (2000)
Model of the disk time evolution in GRS 1915+105 (Janiuk et al 2000). Model explains the lack of state transitions from C to B.
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Radiation pressure instability
M = 108 Msun
Czerny et al. 2009 Predicted outburst duration
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Radiation pressure instability
M = 108 Msun
Czerny et al. 2009
Predicted outburst duration combined with BH masses, luminosities and ages of Young Radio Sources, Wu 2009
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Ionization instabilityResponsible for X-ray novae and dwarf novae outbursts.
May operate in AGN
Janiuk et al. 2004
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Ionization instability•Upper curve: whole disk
•Lower curve: evaporated disk
• interesting for intermittent activity
Janiuk et al. 2004
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Gravitational instability
Collin & Hure 2001
May:-generate stars-speed up inflow-determine BLR
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Nature of viscosity
Magneto-rotational instability, Balbus & Hawley
3D simulations show that this leads to additional faster variability in 'thermal' timescale
Hirose et al. 2009
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Nature of viscosityHirose et al. 2009
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Nature of viscosity
If optical fluctuations in quasars are interpreted as thermal timescale, Starling et al. 2004 obtain:
~ 0.02
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Nature of viscosityAre optical variations in quasars in the timescales of days, down to intra-night micro-variability, due to MRI?
NO
Czerny et al. 2008
YES
Kelly et al. 2009
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Nature of viscosityThe key question to MRI: is radiation pressure instability operating?
May be...
Hirose, Blaes & Krolik 2009, October
No
“The magnetic energy and pressure do scale together as suggested by the dimensional analysis underlying the alpha model, but it is not necessarily because the pressure directly forces the magnetic energy...”
Hirose, Krolik & Blaes 2009, January
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Disk-hot medium interaction
NGC 4151; Czerny, Doroshenko et al.. 2003
• X-ray irradiation of the disk – variable X-rays lead to variable optical/UV flux
• local disk fluctuations - accretion rate perturbation – variable optical flux leads to variable X-ray flux (propagation model of Lyubarsky 1997)
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Disk-hot medium interaction
Short timescales: X-ray irradiation
Anisotropic emission model, Gaskell 2006
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Disk-hot medium interaction
Zdziarski et al. 2010
Damping is very strong if the modulation timescale is shorter than the viscous timescale.
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Disk-hot medium interactionFaster propagation: accreting corona model
Process can be modeled using Markoff chain (e.g. King et al. 2004) but considerable arbitrariness is involved.
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Hot medium origin
• Failed jet/lampost model • Inner ADAF/IRAF• Anchored magnetic flares• Disk evaporation/condensation – accreting
corona• Inflow of ionized material
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Hot medium originMost advanced model: disk evaporation/condensation (Meyer & Meyer-Hoffmeister 1994 +)
Inner cold disk region
Rozanska & Czerny 2000
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Hot medium origin
Complete time evolution of a disk with two-temperature corona; disk condensation/evaporation due to conduction and radiative processes; low accretion rate.
Mayer & Pringle 2007
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Conclusions:
• We need more objects – statistics will translate to flow parameters
• We need more multiwavelength monitoring – statistics again will show trends in parameters of the disk-hot plasma coupling
• We need more advanced global models to test such data – e.g. time-dependent disk with wind and BLR
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Conclusions:We should borrow much more physics from the solar corona in order to understand multi-phase AGN medium...
Hotshot for July 16, 2010
Solar Dynamics Observatory
Hotshot for August 25 2010