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Accretion Disks in AGNsPowerPoint Presentation

Accretion Disks in AGNs

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- Spectral Models: Shane Davis, Ivan Hubeny
- Numerical Simulations: Shigenobu Hirose, Neal Turner
- Simulation Analysis and Theory: Julian Krolik

-Hubeny & Hubeny 1997, 1998; Hubeny et al. (2000, 2001)

- The Good:
- Models account for relativistic disk structure and relativistic
- Doppler shifts, gravitational redshifts, and light bending in
- a Kerr spacetime.
- Models include a detailed non-LTE treatment of abundant
- elements.
- Models include continuum opacities due to bound-free and
- free-free transitions, as well as Comptonization. (No lines
- at this stage, though.)

- The Bad --- Ad Hoc Assumptions:
- Stationary, with no torque inner boundary condition.
- RPtot with constant with radius - determines surface
- density.
- Vertical structure at each radius depends only on height
- and is symmetric about midplane.
- Vertical distribution of dissipation per unit mass assumed
- constant.
- Heat is transported radiatively (and not, say, by bulk
- motions, e.g. convection).
- Disk is supported vertically against tidal field of black
- hole by gas and radiation pressure only.

LMC X-3 in the thermal dominant state

BeppoSAX

RXTE

-Davis, Done, & Blaes (2005)

The same sort of accretion disk modeling that has been

attempted for AGN works pretty well for black hole X-ray binaries

(BHSPEC, Davis et al. 2005, Davis & Hubeny 2006).

Some Recent Observational Developments

That Have Direct Bearing on Our Understanding

Of Accretion Disks in AGN

Spectropolarimetry has succeeded in removing BLR, NLR,

and dust emission in the optical and infrared, revealing the

underlying broadband continuum shape for the first time

(Kishimoto’s talk later in this session).

Ton 202

-Kishimoto et al. (2004)

(2) Microlensing observations have now placed constraints

on the physical size of the optical continuum emitting

region in many QSO’s.

0.33

0.1

-Pooley et al. (2006)

(3) Reverberation mapping leveraged by

BLR radius/continuum luminosity correlations has given

a method of getting approximate black hole masses for

the huge number of SDSS quasars.

5100/4000

4000/2200

2200/1350

-Bonning et al. (2006)

-Bonning et al. (2006)

begone!!!

Thermodynamically consistent, radiation MHD simulations of

MRI turbulence in vertically stratified shearing boxes are telling

us a lot about the likely vertical structure of accretion disks.

Turner (2004): prad>>pgas

Hirose et al. (2006): prad<<pgas

Krolik et al. (2006): prad~pgas

Expect strong (but marginally stable) thermal fluctuations at

low energy and stable (damped) fluctuations at high energy.

- Magnetically supported upper layers decrease density at
- effective photosphere, resulting in increased ionization and
- a hardening of the spectrum.
- Strong (up to factor 100) irregular density inhomogeneities
- exist well beneath photosphere of horizontally averaged
- structure. They will soften the spectrum.
- Actual photosphere is therefore complex and irregular,
- which will reduce intrinsic polarization of emerging photons
- (Coleman & Shields 1990). Magnetic fields may also
- Faraday depolarize the photons (Gnedin & Silant’ev 1978):

Photosphere at

Parker Unstable

Regions

MRI - the source of

accretion power

Parker Unstable

Regions

Photosphere

Overall Vertical Structure of Disk with Prad~Pgas

Pmag>Prad~Pgas

Prad~Pgas>Pmag

Pmag>Prad~Pgas