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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. Accretion. Material falling onto a central object Gravitational binding energy radiation

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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. Accretion • Material falling onto a central object • Gravitational binding energyradiation • Any angular momentumdisk, spin+fieldsjets • It’s everywhere: • Stars • Planetary, debris disks • Compact Objects • (Super)novae • Gamma ray bursts • Active Galactic Nuclei CofC Colloquium

  3. Black Holes • a, M • Innermost stable circular orbit • Photon orbit CofC Colloquium

  4. Astrophysical Black Holes • Types: • Stellar mass (100-101 Msun) • Supermassive (106-109 Msun) • IMBH? (103-106 Msun) • No hard surface • Energy lost to black hole • Inner accretion flow probes strong field GR • Astronomy↔Physics Non-accreting BH CofC Colloquium

  5. The MRI • How does matter lose angular momentum? • Magnetized fluid with Keplerian rotation is unstable: “magnetorotational instability” • Velikhov (1959), Chandrasekhar (1961), Balbus & Hawley (1991) • Transports angular momentum outaccretion! • Toy model based on ideal MHD • Field tied to fluid elements • Tension force along field lines, “spring” CofC Colloquium

  6. Toy Model of the MRI • Radially separated fluid elements differentially rotate. • “Spring” slows down inner element and accelerates outer. • Inner element loses angular momentum and falls inward. Outer element moves outward. • Differential rotation is enhanced and process repeats. • Strong magnetic field growth, saturated growth, turbulence CofC Colloquium

  7. GRMHD Gammie et al (2004) • Advantages: • Fully relativistic • Generate MRI, turbulence, accretion from first principles • Limitations: • Numerical & Difficult • Thermodynamics • Radiation • Spatial extent & Shape • Compare to observations! CofC Colloquium

  8. Galactic Center CofC Colloquium

  9. 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 CofC Colloquium Figure: Moscibrodzka et al. (2009)

  10. Sgr A* VLBI • Largest angular size of any BH • Microarcseconds; baby penguin on moon. • Very long baseline interferometry • High resolution: ~λ/D • Scattering: ~λ2 • Interferometry  Fourier transforms CofC Colloquium

  11. Millimeter Sgr A* Doeleman et al (2008) • Precision black hole astrophysics Gaussian FWHM ~4 Rs! CofC Colloquium

  12. Black Hole Shadow • Signature of event horizon • Sensitive to details of accretion flow Bardeen (1973); Dexter & Agol (2009) Falcke, Melia & Agol (2000) CofC Colloquium

  13. GRMHD Models of Sgr A* Moscibrodzka et al (2009) • mm Sgr A* is an excellent application of GRMHD! • Geometrically thick • Insignificant cooling(?) (L/Ledd ~ 10-9) • Thermal electrons near BH • Not perfect… • Collisionless (mfp = 104 Rs) • Electrons CofC Colloquium

  14. Ray Tracing • Method for performing relativistic radiative transfer • Fluid variables  radiation at infinity • Calculate light rays assuming geodesics. (no refraction) • 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) CofC Colloquium

  15. 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) • Fit images to 1.3mm (230 GHz) VLBI data over grid in Mtor, i, ξ, tobs • Single temperature UIUC CTA Seminar

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

  17. Improved Modeling Dexter et al (2010): • Fit to millimeter flux at .4-1.3mm (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 CofC Colloquium

  18. 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 CofC Colloquium

  19. Comparison to RIAF Values Broderick et al (2009) Sky Orientation Inclination CofC Colloquium

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

  21. Comparison to Observed Flares Marrone et al (2008) Eckart et al (2008) CofC Colloquium

  22. Shadow of Sgr A* Shadow may be detected on chile-lmt, smto-chile baselines; otherwise need south pole. CofC Colloquium

  23. Crescents CofC Colloquium

  24. Constraining Models • Similar standard deviation 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) CofC Colloquium

  25. Tilted Disks • No reason to expect Sgr A* isn’t tilted • Best fit images are still crescents • Shadow still visible CofC Colloquium

  26. Conclusions • Fit 3D GRMHD images 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: Tilted disks, M87, polarization. CofC Colloquium

  27. Event Horizon Telescope From Shep Doeleman’s Decadal Survey Report on the EHT UV coverage (Phase I: black) Doeleman et al (2009) CofC Colloquium

  28. M87 New mass estimate  BH angular size ~4/5 of Sgr A*! (Gebhardt & Thomas 2009) CofC Colloquium

  29. Interferometry Morales & Wythe (2009) CofC Colloquium

  30. Log-Normal Ring Models CofC Colloquium

  31. 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 CofC Colloquium L / LEdd

  32. Sagittarius A* Yuan et al (2003) Dodds-Eden et al (2009) CofC Colloquium

  33. 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 CofC Colloquium L / LEdd

  34. Finite Speed of Light Toy emissivity, i=50 degrees 690 GHz, i=50 degrees CofC Colloquium

  35. Finite Speed of Light • Emission dominated by narrow range in observer time • Time delays are 10-15% effect on light curves CofC Colloquium

  36. 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 CofC Colloquium

  37. Light Curves CofC Colloquium

  38. 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 CofC Colloquium

  39. 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! CofC Colloquium

  40. Modeling • Sample limited by existing 3D simulations • Misleading p(a) • For low spin, need hotter accretion flow CofC Colloquium

  41. 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 CofC Colloquium

  42. Caveats • Limited sample • Constant Ti/Te • Unpolarized millimeter emission • Aligned disk/hole CofC Colloquium

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