Connecting Simulations with Observations of the Galactic Center Black Hole

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Connecting Simulations with Observations of the
Galactic Center Black Hole

• Jason Dexter
• University of Washington

With Eric Agol, Chris Fragile and Jon McKinney
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Exciting Observations of Accreting Black Holes

• X-ray binaries
• State transitions
• QPOs
• Iron lines
• AGN
• QPO(?)
• Microlensing
• Multiwavelength surveys

Fender et al (2004)
Middleton et al (2010)
MCG-6-30-15 Miniutti et al 2007
L / LEdd
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Galactic Center
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Sagittarius A
Jet or nonthermal electrons far from BH Thermal
electrons at BH Simultaneous IR/x-ray flares
close to BH?
no data available
no data available
Charles Gammie
Figure Moscibrodzka et al. (2009)
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Sub-mm Sgr A
Doeleman et al (2008)
Gaussian FWHM 4 Rs!

• Precision black hole astrophysics
• Need accurate emission models

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Black Hole Shadow
Bardeen (1973) Dexter Agol (2009)
Falcke, Melia Agol (2000)

• Signature of event horizon
• Sensitive to details of accretion flow

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Sgr A Models

• Quiescent
• ADAF/RIAF or jet steady state, no MRI, non-rel
• Toy flare models
• -Hotspots
• -Expanding blobs
• -Density perturbations
• But we have a more physical theory!

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Global GRMHD
Gammie et al (2004)

• Advantages
• Fully relativistic, 2D 3D
• Generate MRI, turbulence, accretion
• Limitations
• Thermodynamics
• Radiation
• Spatial extent
• Morphology

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GRMHD Models of Sgr A
Moscibrodzka et al (2009)

• Sub-mm Sgr A is an excellent application of
  GRMHD!
• Thick accretion flow (ADAF/RIAF)
• Insignificant cooling(?) (L/Ledd 10-9)
• Thermal electrons near BH
• Not perfect
• Collisionless plasma (mfp 104 Rs)
• Electrons

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Ray Tracing

• Method for performing relativistic radiative
  transfer
• Fluid variables ? emission at infinity
• Calculate light rays assuming geodesics. (? gtgt
  ?p, ?c)
• Observer camera? constants of motion
• Trace backwards and integrate along portions of
  rays intersecting flow.
• Intensities?Image, many frequencies?spectrum,
  many times?light curve

?
Schnittman et al (2006)
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Modeling

• Dexter, Agol Fragile (2009)
• Geodesics from public, analytic code geokerr
  (Dexter Agol 2009)
• Time-dependent, relativistic radiative transfer
• 3D simulation from Fragile et al (2007)
• Need 3D for accurate MRI, variability
• a0.9, doesnt conserve energy!
• Fit images to 1.3mm (230 GHz) VLBI data over grid
  in Mtor, i, ?, tobs
• Unpolarized single temperature

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GRMHD Fits to VLBI Data
Dexter, Agol Fragile (2009) Doeleman et al
(2008)
i10 degrees
i70 degrees
?100 µas?
?10,000 km?
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Light Curves
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Comparison to Observed Flares
Eckart et al (2008)
Marrone et al (2008)
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Improved Modeling

• Dexter et al (2010 submitted)
• Sub-mm spectral index (Marrone 2006)
• Add simulations from McKinney Blandford (2009)
  Fragile et al (2009)
• Two-temperature models (parameter Ti/Te Goldston
  et al 2005, Moscibrodzka et al 2009)
• Joint fits to spectral, VLBI data over grid in
  Mtor, i, a, Ti/Te
• Angle-dependent emissivity (Leung et al 2010)

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Improved Modeling

• Sample limited by existing 3D simulations
• Misleading p(a)
• For low spin, need hotter accretion flow

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Parameter Estimates
35 -15
Sky Orientation

• i 50 degrees
• Te /1010 K 5.43.0
• ? -23 degrees
• dM/dt 5 x 10-9 Msun yr-1
• All to 90 confidence

Inclination
97 -22
Electron Temperature
Accretion Rate
15 -2
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Comparison to RIAF Values
Broderick et al (2009)
Sky Orientation
Inclination
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Face-on Fits

• Excellent fits to 1.3mm VLBI at all inclinations
  with 90h, TiTe (Dexter, Agol and Fragile 2009)
• Low inclinations now ruled out by
• Spectral index constraint (Moscibrodzka et al
  2009)
• Scarcity of VLBI fits in other models

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Millimeter Flares

• Models reproduce observed flare duration,
  amplitude, frequency
• Stronger variability at higher frequency

Solid 230 GHz Dotted 690 GHz
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Millimeter Flares

• Strong correlation with accretion rate
  variability
• Approximate emissivity
• J? nBa, a 1-2.
• Isothermal emission region, ?/?c 10.
• Not heating from magnetic reconnection

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Finite Speed of Light
Toy emissivity, i50 degrees
690 GHz, i50 degrees
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Finite Speed of Light

• Emission dominated by narrow range in observer
  time
• Time delays are 10-15 effect on light curves

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Shadow of Sgr A
Shadow may be detected on chile-lmt, smto-chile
baselines otherwise need south pole.
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Crescents
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Constraining Models

• Similar variance to Fish et al (2009)
• Chile/Mexico are best bets for further
  constraining models
• Simultaneous measurement of total flux at 345 GHz
  would provide a significant constraint

230 GHz
345 GHz
Fish et al (2009)
Dexter et al (2010)
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Caveats

• Limited sample
• Constant Ti/Te
• Unpolarized millimeter emission

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Conclusions

• Fit 3D GRMHD images/light curves of Sgr A to mm
  observations
• Estimates of inclination, sky orientation agree
  with RIAF fits (Broderick et al 2009)
• Electron temperature well constrained
• Consistent, but independent accretion rate
  constraint
• Reproduce observed mm flares
• LMT-Chile next best chance for observing shadow
• Future polarized emission, tilted disks, M87.

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M87
New mass estimate ? BH angular size 4/5 of Sgr
A! (Gebhardt Thomas 2009)
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Tilted Disks
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Interferometry
Morales Wythe (2009)
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Log-Normal Ring Models
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Event Horizon Telescope
From Shep Doelemans Decadal Survey Report on the
EHT
UV coverage (Phase I black)
Doeleman et al (2009)
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Exciting Observations of Accreting Black Holes

• X-ray binaries
• State transitions
• QPOs
• Iron lines
• AGN
• QPO(?)
• Microlensing
• Multiwavelength surveys

Steiner et al. 2010
Schmoll et al (2009)
Fairall-9
LMC X-3 1983 2009
Morgan et al (2010)
SWIFT J1247
L / LEdd
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Sagittarius A
Yuan et al (2003)
Dodds-Eden et al (2009)