# Presentation: 550624

## The Central Engine in AGN:Back to Basics

- Collaborators:
- Kris Beckwith, Omer Blaes, Shane Davis, Jean-Pierre De Villiers, John Hawley, Shigenobu Hirose, Jim Stone

## Real Central Engines

- Big Blue Bump

- hard X-rays

- dust reprocessed IR

## A Central Engine As Some Imagine It

- Mass

- Light

- Jet (optional)

## Order of Magnitude Estimates:The Big Problems

- Accreting ~1 L46 solar mass/year:
- reducing its specific angular momentum from ~1029 cm2 s-1 to ~1024 cm2 s-1; with efficiency great enough to be consistent with the remnant mass  budget; with what spin distribution?

- Tin ~ 105  (L/LE)1/4M8-1/4 K:
- origin of hard X-rays?

- ~*O*(0.1) radio-loud:
- with Lkin,jet ~ Lrad; and controlled by what parameter?

## A Central Engine as Traditionally Seen

- N-T (Wms = 0)

- B-Z

- Mass

- Light

- Jet (optional)

## A Central Engine as We’d Like to Understand It

- Mass

- Light

- Jet (parameter)

## The Goal: From Basic Physical Mechanisms to Light and Outflows

- In stars, nuclear reactions release heat.  Energy is carried to the surface by photon diffusion and convection, then radiated at the surface.

- In accretion disks, correlated MHD turbulence transfers angular momentum and leads to dissipation into heat.  Energy is carried to the surface by photon diffusion,.....

## A Three-Step Program

- Global disk calculations to find the radial stress profile and the overall disk structure
- Local shearing-box studies to find the internal vertical structure
- Sum over local disk atmospheres to find the observed spectrum

## Global GR/MHD(more details tomorrow in Hawley’s talk)

- Kerr metric
- MHD approximation
- no radiation forces, no radiation losses
- 	3d, internal energy only (De Villiers-Hawley)
- 	2d, total energy (McKinney-Gammie)

- Simulations essential

## Generic Structures

## Results of Global Simulations I:Non-zero Inner Disk Stress

## Electromagnetic Limits to Spin-Up

| a/M | lm | lEM |
| --- | --- | --- |
| 0.0 | 3.26 | -0.06 |
| 0.5 | 2.77 | -0.13 |
| 0.9 | 2.23 | -0.39 |
| 0.93 | 2.11 | -0.54 |
| 0.95 | 2.08 | -0.83 |
| 0.99 | 1.85 | -1.70 |

## Global Result II: Larger Accretion Efficiency?

- Criterion: Must conserve energy in time-steady disk, consistent with stress
- Best candidate: uniform resistivity, heating proportional to |J|2

## But What Fraction of the Photons Escape---and With What Doppler Shift?

## Estimated Accretion Efficiency

| a/M |  |  |
| --- | --- | --- |
| 0.0 | 0.055--0.056 | 0.067--0.07 |
| 0.5 | 0.077--0.079 | 0.13--0.14 |
| 0.9 | 0.137--0.145 | 0.16--0.18 |
| 0.998 | 0.250--0.290 | 0.29--0.41 |

## Global Result III: Jets(more during Hawley’s talk tomorrow)

## Substantial Jet Energy Efficiency for Rapid Spin

| a/M |  |  |  |
| --- | --- | --- | --- |
| -0.9 |  | 0.023 | 0.039 |
| 0.0 |  | 0.0003 | 0.057 |
| 0.5 |  | 0.0063 | 0.081 |
| 0.9 |  | 0.046 | 0.16 |
| 0.93 |  | 0.038 | 0.17 |
| 0.95 |  | 0.072 | 0.10 |
| 0.99 |  | 0.21 | 0.26 |

## Radiation MHD Simulations

- MHD approximation
- 3-d shearing box
- total energy: grid-scale dissipation of magnetic field 	and kinetic energy goes into heat
- flux-limited diffusion with Rosseland mean opacity

## Radiation Shearing-Box Results:Structure in the Gas Pressure-Dominated Regime

- gas

- magnetic

- radiation

- The upper layers are magnetically-supported

- r = 300 rg      L = 0.14LE
- M = 6.6Msun (for simpler opacity)

## Spectral Formation

- Modified Hubeny code: for a given ring,
- 	1-d, plane-parallel, time-steady
- 	hydrostatic equilibrium
- 	thermal, photoionization, excited state equilibrium
- 	detailed multi-group, multi-frequency transfer
- 	continuum opacity only

## Consequences for Emitted Spectrum

- Magnetic support extends the atmosphere, reduces its density, leads to an extended scattering-dominated atmosphere and stronger departures from LTE

- CVI K-edge

- harder modified black-body tail

## Conclusions

- Beginning to be possible to calculate AGN disk properties from (almost) first principles
- Radiative efficiency larger, and  no longer a function solely of spin?
- Magnetic support can affect emitted spectrum
- Substantial EM angular momentum loss,
-     strong Poynting jet when a/M > 0.9