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Connecting Simulations with Observations of the Galactic Center Black Hole

Connecting Simulations with Observations of the Galactic Center Black Hole. Jason Dexter University 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

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Connecting Simulations with Observations of the Galactic Center Black Hole

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  1. Connecting Simulations with Observations of the Galactic Center Black Hole Jason Dexter University of Washington With Eric Agol, Chris Fragile and Jon McKinney

  2. 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 UIUC CTA Seminar L / LEdd

  3. Galactic Center UIUC CTA Seminar

  4. 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 UIUC CTA Seminar Figure: Moscibrodzka et al. (2009)

  5. Sub-mm Sgr A* Doeleman et al (2008) • Precision black hole astrophysics • Need accurate emission models Gaussian FWHM ~4 Rs! UIUC CTA Seminar

  6. Black Hole Shadow • Signature of event horizon • Sensitive to details of accretion flow Bardeen (1973); Dexter & Agol (2009) Falcke, Melia & Agol (2000) UIUC CTA Seminar

  7. 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

  8. Global GRMHD Gammie et al (2004) • Advantages: • Fully relativistic, 2D & 3D • Generate MRI, turbulence, accretion • Limitations: • Thermodynamics • Radiation • Spatial extent • Morphology UIUC CTA Seminar

  9. 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 UIUC CTA Seminar

  10. Ray Tracing • 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. • IntensitiesImage, many frequenciesspectrum, many timeslight curve  Schnittman et al (2006) UIUC CTA Seminar

  11. 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

  12. GRMHD Fits to VLBI Data i=10 degrees i=70 degrees Dexter, Agol & Fragile (2009); Doeleman et al (2008) 100 μas 10,000 km UIUC CTA Seminar

  13. Light Curves UIUC CTA Seminar

  14. Comparison to Observed Flares Marrone et al (2008) Eckart et al (2008) UIUC CTA Seminar

  15. 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) UIUC CTA Seminar

  16. Improved Modeling • Sample limited by existing 3D simulations • Misleading p(a) • For low spin, need hotter accretion flow UIUC CTA Seminar

  17. Parameter Estimates +35 -15 Sky Orientation Inclination • 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 +97 -22 Electron Temperature Accretion Rate +15 -2 UIUC CTA Seminar

  18. Comparison to RIAF Values Broderick et al (2009) Sky Orientation Inclination UIUC CTA Seminar

  19. Face-on Fits • 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 UIUC CTA Seminar

  20. Millimeter Flares • Models reproduce observed flare duration, amplitude, frequency • Stronger variability at higher frequency Solid – 230 GHz Dotted – 690 GHz UIUC CTA Seminar

  21. Millimeter Flares • Strong correlation with accretion rate variability • Approximate emissivity: • Jν ~ nBα, α ≈ 1-2. • Isothermal emission region, ν/νc ≈ 10. • Not heating from magnetic reconnection UIUC CTA Seminar

  22. Finite Speed of Light Toy emissivity, i=50 degrees 690 GHz, i=50 degrees UIUC CTA Seminar

  23. Finite Speed of Light • Emission dominated by narrow range in observer time • Time delays are 10-15% effect on light curves UIUC CTA Seminar

  24. Shadow of Sgr A* Shadow may be detected on chile-lmt, smto-chile baselines; otherwise need south pole. UIUC CTA Seminar

  25. Crescents UIUC CTA Seminar

  26. 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) UIUC CTA Seminar

  27. Caveats • Limited sample • Constant Ti/Te • Unpolarized millimeter emission UIUC CTA Seminar

  28. 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

  29. M87 New mass estimate  BH angular size ~4/5 of Sgr A*! (Gebhardt & Thomas 2009) UIUC CTA Seminar

  30. Tilted Disks UIUC CTA Seminar

  31. Interferometry Morales & Wythe (2009) UIUC CTA Seminar

  32. Log-Normal Ring Models UIUC CTA Seminar

  33. Event Horizon Telescope From Shep Doeleman’s Decadal Survey Report on the EHT UV coverage (Phase I: black) Doeleman et al (2009) UIUC CTA Seminar

  34. Exciting Observations of Accreting Black Holes Steiner et al. 2010 Schmoll et al (2009) • X-ray binaries • State transitions • QPOs • Iron lines • AGN • QPO(?) • Microlensing • Multiwavelength surveys Fairall-9 LMC X-3: 1983 – 2009 Morgan et al (2010) SWIFT J1247 UIUC CTA Seminar L / LEdd

  35. Sagittarius A* Yuan et al (2003) Dodds-Eden et al (2009) UIUC CTA Seminar

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