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 DexterUniversity of Washington
With Eric Agol, Chris Fragile and Jon McKinney
Exciting Observations of Accreting Black Holes
• X-ray binaries– State transitions– QPOs– Iron lines
• AGN– QPO(?)– Microlensing– Multiwavelength
surveysUIUC CTA Seminar 2L / LEdd
MCG-6-30-15 Miniutti et al 2007
Fender et al (2004)Middleton et al (2010)
Galactic Center
UIUC CTA Seminar 3
Sagittarius A*
UIUC CTA Seminar 4
Jet or nonthermal electrons far from BH
Thermal electrons at BH
Simultaneous IR/x-ray flares close to BH?
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ata
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ata
avai
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eCharles Gammie
Sub-mm Sgr A*
• Precision black hole astrophysics• Need accurate emission models
5UIUC CTA Seminar
Doeleman et al (2008)
Gaussian FWHM ~4 Rs!
Black Hole Shadow
• Signature of event horizon• Sensitive to details of accretion flow
Bardeen (1973); Dexter & Agol (2009) Falcke, Melia & Agol (2000)
6UIUC CTA Seminar
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!
UIUC CTA Seminar 7
Global GRMHD
• Advantages:– Fully relativistic, 2D & 3D– Generate MRI, turbulence,
accretion
• Limitations:– Thermodynamics– Radiation– Spatial extent– Morphology
UIUC CTA Seminar 8
Gammie et al (2004)
GRMHD Models of Sgr A*
• 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)
– ElectronsUIUC CTA Seminar 9
Moscibrodzka et al (2009)
Ray Tracing
UIUC CTA Seminar 10
• Method for performing relativistic radiative transfer
• Fluid variables emission at infinity
• Calculate light rays assuming geodesics. (ω >> ωp, ωc)
• Observer “camera” constants of motion
• Trace backwards and integrate along portions of rays intersecting flow.
• IntensitiesImage, many frequenciesspectrum, many timeslight curve
Schnittman et al (2006)
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• a=0.9, doesn’t conserve energy!
• Fit images to 1.3mm (230 GHz) VLBI data over grid in Mtor, i, ξ, tobs
• Unpolarized; single temperature
UIUC CTA Seminar 11
GRMHD Fits to VLBI Data
UIUC CTA Seminar 12
Dexter, Agol & Fragile (2009); Doeleman et al (2008)i=10 degrees i=70 degrees
10,000 km
100 μas
Light Curves
UIUC CTA Seminar 13
Comparison to Observed Flares
UIUC CTA Seminar 14
Eckart et al (2008)Marrone et al (2008)
Improved ModelingDexter 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)
UIUC CTA Seminar 15
Improved Modeling
UIUC CTA Seminar 16
• Sample limited by existing 3D simulations
• Misleading p(a)– For low spin, need
hotter accretion flow
Parameter Estimates• i = 50 degrees
• Te /1010 K = 5.4±3.0
• ξ = -23 degrees
• dM/dt = 5 x 10-9 Msun yr-1
• All to 90% confidence
UIUC CTA Seminar 17
+35-15
+97-22
Inclination
Electron Temperature
Sky Orientation
Accretion Rate+15-2
Comparison to RIAF Values
UIUC CTA Seminar 18
Broderick et al (2009)
Inclination Sky Orientation
Face-on Fits
UIUC CTA Seminar 19
• Excellent fits to 1.3mm VLBI at all inclinations with 90h, Ti=Te (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
Millimeter Flares• Models
reproduce observed flare duration, amplitude, frequency
• Stronger variability at higher frequency
UIUC CTA Seminar 20
Solid – 230 GHz Dotted – 690 GHz
Millimeter Flares
UIUC CTA Seminar 21
• Strong correlation with accretion rate variability
• Approximate emissivity:– Jν ~ nBα, α ≈ 1-2.
– Isothermal emission region, ν/νc ≈ 10.
– Not heating from magnetic reconnection
Finite Speed of Light
UIUC CTA Seminar 22
Toy emissivity, i=50 degrees 690 GHz, i=50 degrees
Finite Speed of Light
UIUC CTA Seminar 23
• Emission dominated by narrow range in observer time
• Time delays are 10-15% effect on light curves
Shadow of Sgr A*
UIUC CTA Seminar 24
Shadow may be detected on chile-lmt, smto-chile baselines; otherwise need south pole.
Crescents
UIUC CTA Seminar 25
Constraining Models
UIUC CTA Seminar 26
• 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
Fish et al (2009) Dexter et al (2010)
230 GHz 345 GHz
Caveats
• Limited sample
• Constant Ti/Te
• Unpolarized millimeter emission
UIUC CTA Seminar 27
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.
UIUC CTA Seminar 28
M87
UIUC CTA Seminar 29
New mass estimate BH angular size ~4/5 of Sgr A*! (Gebhardt & Thomas 2009)
Tilted Disks
UIUC CTA Seminar 30
Interferometry
UIUC CTA Seminar 31
Morales & Wythe (2009)
Log-Normal Ring Models
UIUC CTA Seminar 32
Event Horizon Telescope
UIUC CTA Seminar 33
UV coverage (Phase I: black)
From Shep Doeleman’s Decadal Survey Report on the EHT
Doeleman et al (2009)
Exciting Observations of Accreting Black Holes
• X-ray binaries– State transitions– QPOs– Iron lines
• AGN– QPO(?)– Microlensing– Multiwavelength
surveysUIUC CTA Seminar 34L / LEdd
SWIFT J1247
LMC X-3: 1983 – 2009
Steiner et al. 2010
Morgan et al (2010)
Fairall-9
Schmoll et al (2009)
Sagittarius A*
UIUC CTA Seminar 35
Dodds-Eden et al (2009)
Yuan et al (2003)
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