The Submillimeter Bump ofSgr A* from GRMHD Simulations

Jason DexterUniversity of Washington

With Eric Agol, Chris Fragile and Jon McKinney

Sub-mm Sgr A*

• Precision black hole astrophysics• Probe strong gravity!

2Probing Strong Gravity

Doeleman et al (2008)

~4 Rs!

Yuan et al (2003)

Black Hole Shadow

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

Bardeen (1973); Dexter & Agol (2009) Falcke, Melia & Agol (2000)

3Probing Strong Gravity

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, ξ, tobs

• Unpolarized; single temperature

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Schnittman et al (2006)

GRMHD Fits to VLBI Data

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Dexter, Agol & Fragile (2009); Doeleman et al (2008)i=10 degrees i=70 degrees

10,000 km

100 μas

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• i = 50 degrees

• Te /1010 K = 5.4±3.0

• ξ = -23 degrees

• All to 90% confidence• Results agree with

Broderick et al (2009)

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+35-15

+97-22

Spin Inclination

Electron Temperature

Sky Orientation

Millimeter Flares• Models reproduce

observed mm flare duration, amplitude, frequency

• Strong correlation with accretion rate

• Not caused by heating from magnetic reconnection

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Solid – 230 GHz Dotted – 690 GHz

Shadow of Sgr A*

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Shadow may be detected on chile-lmt, smto-chile baselines; otherwise need south pole.

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

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Eckart et al (2008)Marrone et al (2008)

Spectra

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Visibility Variance

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Accretion Rate Variability

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RIAF Fits

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Broderick et al (2009)

Event Horizon Telescope

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UV coverage (Phase I: black)

From Shep Doeleman’s Decadal Survey Report on the EHT

Doeleman et al (2009)