Accretion Disks in AGNs

Omer BlaesUniversity of California, Santa Barbara

Collaborators

• Spectral Models: Shane Davis, Ivan Hubeny

• Numerical Simulations: Shigenobu Hirose, Neal Turner

• Simulation Analysis and Theory: Julian Krolik

i

AGNSPEC

-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 beenattempted for AGN works pretty well for black hole X-ray binaries(BHSPEC, Davis et al. 2005, Davis & Hubeny 2006).

Some Recent Observational DevelopmentsThat Have Direct Bearing on Our Understanding

Of Accretion Disks in AGN(1) 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.

-Pooley et al. (2006)

0.1

0.33

-Dai et al. (2006)

-Bonning et al. (2006)

5100/4000

4000/2200

2200/1350

(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.

5100/1350

-Bonning et al. (2006)

-Davis et al. (2006)

AGNSPEC

Blackbodies

(F )

-Davis et al. (2006)

SDSS data

AGNSPEC

AGNSPECWith

E(B-V)=0.04

(4000-2200) (2200-1450)

begone!!!Thermodynamically consistent, radiation MHD simulations ofMRI turbulence in vertically stratified shearing boxes are tellingus a lot about the likely vertical structure of accretion disks.

Turner (2004): prad>>pgasHirose et al. (2006): prad<<pgasKrolik et al. (2006): prad~pgas

Radiation

Gas

Magnetictimes 10

Expect strong (but marginally stable) thermal fluctuations atlow energy and stable (damped) fluctuations at high energy.

Gas

Radiation

Magnetic

GravityTotal

C

VI K

-ed

ge

-Blaes et al. (2006)

No magneticfields

With magneticfields

Complex Structure of Surface Layers

Photon BubbleShock Train???

Photosphere

Parker

Spectral Consequences

• 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):

0.8TPmagPrad

1/ 2

2 radians

Overall Vertical Structure of Disk with Prad~Pgas

MRI - the source ofaccretion power

Photosphere

Photosphere

Parker UnstableRegions

Parker UnstableRegions

Pmag>Prad~Pgas

Pmag>Prad~Pgas

Prad~Pgas>Pmag