The Submillimeter Bump of Sgr A* from GRMHD Simulations

1
The Submillimeter Bump ofSgr A from GRMHD
Simulations

• Jason Dexter
• University of Washington

With Eric Agol, Chris Fragile and Jon McKinney
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Sub-mm Sgr A
Doeleman et al (2008)
?

• Precision black hole astrophysics
• Probe strong gravity!

4 Rs!
Yuan et al (2003)
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Black Hole Shadow
Bardeen (1973) Dexter Agol (2009)
Falcke, Melia Agol (2000)

• Sensitive to details of accretion flow
• 3D GRMHD!

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Modeling

• Geodesics from Dexter Agol (2009)
• Time-dependent, relativistic radiative transfer
• Simulation from Fragile et al (2007)
• Fit images to VLBI data over grid in Mtor, i, ?,
  tobs
• Unpolarized single temperature

Schnittman et al (2006)
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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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Improved Modeling

• Sub-mm spectral index (Marrone 2006)
• Add simulations from McKinney Blandford (2009)
  Fragile et al (2009)
• Two-temperature models (parameter Ti/Te)
• 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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Parameter Estimates
35 -15

• i 50 degrees
• Te /1010 K 5.43.0
• ? -23 degrees
• All to 90 confidence
• Results agree with Broderick et al (2009)

Inclination
Spin
97 -22
Sky Orientation
Electron Temperature
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Millimeter Flares

• Models reproduce observed mm flare duration,
  amplitude, frequency
• Strong correlation with accretion rate
• Not caused by heating from magnetic reconnection

Solid 230 GHz Dotted 690 GHz
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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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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
• Reproduce observed mm flares
• LMT-Chile next best chance for observing shadow
• Future polarized emission, tilted disks.

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Comparison to Observed Flares
Eckart et al (2008)
Marrone et al (2008)
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Spectra
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Visibility Variance
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Accretion Rate Variability
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RIAF Fits
Broderick et al (2009)
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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)