Radiative Models of Sgr A* and M87* from

Relativistic MHD Simulations

Jason DexterUniversity of Washington /

UC Berkeley

With Eric Agol, Chris Fragile and Jonathan McKinney

Sagittarius A*

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Jet or nonthermal electrons far from BH

Thermal electrons at BH

Simultaneous IR/X-ray flares close to BH?

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eCharles Gammie, Rainer Schödel

Millimeter VLBI of Sgr A*

• Precision black hole astrophysics

3AHAR 2011: The Central Kiloparsec

Doeleman et al. (2008)

Gaussian FWHM ~4 Rs!

Black Hole Images & Shadows• Sensitive to

viewing geometry & details of accretion flow– Need

accurate theoretical predictions!

Bardeen (1973); Dexter & Agol (2009)

Falcke, Melia & Agol (2000)

4AHAR 2011: The Central Kiloparsec

Broderick & Loeb (2009)

Dexter et al. (2009, 2010)

Models of Sgr A*• Semi-analytic:

– RIAF or jet• Narayan & Yi (1995), Yuan et al. (2003), Broderick et al. (2009, 2010,

2011), Falcke & Markoff (2000)

– Hotspots/expanding blobs• Broderick & Loeb (2006), Eckart et al. (2006), Yusef-Zadeh et al.

(2006)

• MHD Simulations:– Non-relativistic

• Goldston et al. (2005), Chan et al. (2008), Huang et al. (2009)

– Axisymmetric or averaged GRMHD• Noble et al. (2007), Moscibrodzka et al. (2009), Hilburn et al. (2009)

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GRMHD Models of Sgr A*

• 3D, time-dependent GRMHD great for mm Sgr A*– Thick, MRI-driven accretion flow – Insignificant cooling(?) – Synchrotron radiation near BH

• Not perfect…– Collisionless plasma (mfp = 104 Rs)– No electrons

• Assume constant Ti/Te

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Moscibrodzka et al. (2009)

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• Assume light rays are geodesics:– geokerr, Dexter & Agol (2009)

• 5 (4) Simulations: – Fragile et al. (2007, 2009)– McKinney & Blandford (2009)

• Synchrotron emissivity: – Leung et al. (2011)

• Joint fits to spectral & VLBI data:– Marrone 2006, Doeleman et al.

2008, Fish et al. 2011– Parameters: dM/dt, i, a, Ti/Te

Ray Tracing

Schnittman et al. (2006)

Parameter Estimates• i = 60 degrees

• ξ = -70 degrees

• Te /1010 K = 6 ± 2

• dM/dt = 3 x 10-9 Msun yr-1

• All to 90% confidence

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+15-15

+86-15

+7-1

Dexter et al. (2010, 2011)

Sky Orientation

Inclination

Electron Temperature

Accretion Rate

All VLBI 2007

Millimeter Flares• Correlation with

accretion rate

• Driven by magnetic turbulence

• Models reproduce observed mm flares

• IR/X-ray?AHAR 2011: The Central Kiloparsec 9

Solid – 230 GHz (1.3mm) Dotted – 690 GHz (0.4mm)

Black Hole Shadow in Sgr A*

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Shadow may be detected on Chile-Mexico baseline (in closure phase too)

Shadow

230 GHz

345 GHz

M87• 1600 MSgr A* at 2000 DSgr A*

• Jet launching physics?• Known viewing geometry?

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7mm Junor et al. (1999)

2cm Kovalev et al. (2007)

Hubble

M87* Models• Simulation: McKinney & Blandford (2009)• Jet: B2 > ρc2, ujet=ηB2

• Representative models: Disk/jet or jet• Unlike previous models

– Can’t have disk peak in radio– Can’t match radio at all

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Broderick & Loeb ( 2009)

Images & Visibilities• Images are still crescents!• Gaussian size: 36-41 μas• Shadow on Hawaii-Mexico or Mexico-Chile

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Dexter et al. (2011)

Conclusions• Millimeter images/light curves of Sgr A* and M87*

from GRMHD simulations• Sgr A* (Dexter et al. 2009, 2010, 2011)

– Excellent fits with GRMHD & images are crescents!– Estimates for viewing geometry and physical conditions – Reproduce observed mm flares– Mexico—Chile next best chance for observing shadow

• M87 (Dexter et al. 2011)– Disk/jet or jet models– Predict 36-41 μas size, shadow on Hawaii—Chile or Mexico

—Chile– Robust results if geometry is correct

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Tilted Sgr A*

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• No reason to expect Sgr A* isn’t tilted• Unconstrained parameters• Best fit images are still crescents• Shadow still visible

Shadow

RIAF Fits

AHAR 2011: The Central Kiloparsec 16Dexter et al. (2010, 2011), Broderick et al. (2010)

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Shadow in Closure Phase

Visibility Variance

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Spectra

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Accretion Rate Variability

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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)

Comparison to Observed Flares

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

Galactic Center Black Hole

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