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Radiative Models of Sagittarius A* and M87 from Relativistic MHD Simulations

Radiative Models of Sagittarius A* and M87 from Relativistic MHD Simulations. Jason Dexter 7/8/2011. Black Holes. a, M, (Q) Innermost stable circular orbit Circular photon orbit. Accretion. Material falling onto a central object Gravitational binding energy radiation

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Radiative Models of Sagittarius A* and M87 from Relativistic MHD Simulations

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  1. Radiative Models of Sagittarius A* and M87 from Relativistic MHD Simulations Jason Dexter 7/8/2011

  2. Black Holes • a, M, (Q) • Innermost stable circular orbit • Circular photon orbit Final Exam

  3. Accretion • Material falling onto a central object • Gravitational binding energyradiation • Any angular momentumdisk, rotation+fieldsjets • It’s everywhere: • Stars • Protostellar, debris disks • Compact Objects • (Super)novae • X-ray & γ-ray bursts • Active Galactic Nuclei (AGN) • X-ray Binaries Final Exam

  4. Accreting Black Holes • Power brightest objects in Universe (GRB, AGN) • Center of every galaxy? Final Exam

  5. Accreting Black Holes • Types: • Stellar mass (100-1 Msun) • Supermassive (106-9 Msun) • IMBH? (103-6 Msun) • No hard surface • Cold, bright, thin (‘thin disk’) or hot, thick, often faint (‘ADAF’ or ‘RIAF’) • Thin disk: AGN, ‘thermal’ state • ADAF: Sgr A*, M87, LLAGN, ‘quiescent’ • Inner accretion flow probes strong field GR Narayan & Quataert (2005) Final Exam

  6. Accretion Theory • Time-steady, axisymmetric, vertically-averaged • No accretion mechanism • Predictive, qualitatively correct Steiner et al. (2010) Kriss et al. (1999)) Reynolds et al. (1996) Final Exam

  7. Accretion Theory • Thin disk problems: • Thermal & inflow instabilities • UV Emission, Simultaneous variability, Microlensing Sizes • ADAF  RIAF to explain linear polarization of Sgr A* (Agol 2000, Quataert & Gruzinov 2000) Dexter & Agol (2011) Final Exam

  8. The MRI • How does matter lose angular momentum? • Magnetized fluid with Keplerian rotation is unstable: “magnetorotational instability” • Velikhov (1959), Chandrasekhar (1961), Balbus & Hawley (1991) • Nonlinear, saturates, drives magnetic turbulence • Transports angular momentum outaccretion! • Pro: physical accretion, con: numerical computation Final Exam

  9. GRMHD Gammie et al. (2004) • Advantages: • Fully relativistic • Generate MRI, turbulence, accretion from first principles • Limitations: • Numerical & Difficult • Thermodynamics • Radiation • Spatial extent & shape (thick!) • Compare to observations! Final Exam

  10. Tilted GRMHD • Black hole spin axis not aligned with torus axis. • Thin: Alignment • Thick: • Precession • Standing shocks, plunging streams. • Compare to observations! Bardeen & Petterson (1975), Fragile et al. (2000) Fragile et al. (2007), Fragile & Blaes (2008) Final Exam

  11. Radiative Transfer Kasen et al. (2009) • Connecting theory & observation requires photons • Examples across astrophysics: • Numerical simulations of galaxy formation, supernovae, irradiated exoplanets  Governato et al. (2009) Final Exam

  12. Ray Tracing • Method for performing relativistic radiative transfer • Fluid variables  radiation at infinity • Calculate light rays assuming geodesics (no refraction) • Trace backwards and integrate radiative transfer equation along portions of rays intersecting flow. • IntensitiesImage, many frequenciesspectrum, many timeslight curve  Schnittman et al. (2006) Final Exam

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

  14. grtrans • Relativistic radiative transfer via ray tracing • To compute observables: • Photon trajectories (geokerr, Dexter & Agol 2009) • Dynamical model (GRMHD) • Particle model (electrons) • Convert code to physical units with MBH, dM/dt • Emission/absorption (unpol synchrotron) • Flexible, applicable to non-BH problems Final Exam

  15. Radiation Edge of Tilted Disks • Inner edge usually associated with ISCO • Independent of spin for 15 degree tilt! Dexter & Fragile (2011) Final Exam

  16. Inner Edge of Tilted Disks Untilted Tilted • Non-axisymmetric standing shocks transport angular momentum, truncate disk Angular momentum deficit increases with spin Top: Angular momentum Bottom: Entropy Final Exam

  17. Galactic Center Final Exam

  18. 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 Final Exam Figure: Moscibrodzka et al. (2009)

  19. Millimeter VLBI of Sgr A* Doeleman et al (2008) Gaussian FWHM ~4 Rs! • Precision black hole astrophysics Arizona—Hawaii baseline Final Exam

  20. GRMHD Models of Sgr A* Moscibrodzka et al. (2009) • mm Sgr A* is an excellent application of GRMHD! • Particle: Maxwell with constant Ti/Te, emission: synchrotron radiation • 5 (4) simulations: Fragile et al. (2007, 2009); McKinney & Blandford (2009) • mm images over grid in: • dM/dt, i, a, Ti/Te • Joint fits to spectral (Marrone 2006), VLBI data (Doeleman et al. 2008, Fish et al. 2011) Final Exam

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

  22. Parameter Estimates +15 -15 • i = 60 degrees • ξ = -70 degrees • Te /1010 K = 6 ± 2 • dM/dt = 3 x 10-9 Msun yr-1 • All to 90% confidence All VLBI 2007 Sky Orientation +86 -15 Inclination Electron Temperature Accretion Rate +7 -1 Dexter et al. (2010) Final Exam

  23. Comparison to RIAF Values Sky Orientation All VLBI 2007 Inclination Broderick et al. (2011) Final Exam

  24. Millimeter Flares • Correlation with accretion rate • Driven by magnetic turbulence • Models reproduce observed mm flares • IR/X-ray? Solid – 230 GHz (1.3mm) Dotted – 690 GHz (0.4mm) Final Exam

  25. Comparison to Observed Flares Marrone et al. (2008) Eckart et al. (2008) Final Exam

  26. Black Hole Shadow in Sgr A* 230 GHz Shadow 345 GHz Shadow may be detected on Chile-Mexico baseline (in closure phase too) Final Exam

  27. Crescents • Images: gravitational lensing & doppler beaming • Ring, crescent, Gaussian • Wide range of physical models Final Exam

  28. Tilted Sgr A* • Nice picture, but no reason to expect Sgr A* isn’t tilted • Unconstrained parameters • Best fit images are still crescents • Shadow still visible Shadow Final Exam

  29. M87 7mm Junor et al. (1999) • 1600 MSgr A* at 2000 DSgr A* • Jet launching physics? • Known viewing geometry? Hubble 2cm Kovalev et al. (2007) Final Exam

  30. Modeling M87 McKinney & Blandford (2009) • mm-VLBI: Large mass, long timescales, northern sky, no scattering, direct image! • Particle: disk/jet, emission: synchrotron • Magnetic jet, let ujet=ηB2 • n(γ)=Aγ-p, γ > γmin • Inner radii only Final Exam

  31. Fiducial Models • Representative models: Disk/jet or jet • Unlike previous models • Can’t have disk peak in radio • Can’t match radio at all! (similar to Sgr A*) Broderick & Loeb ( 2009) Final Exam

  32. Images & Visibilities • Images are still crescents! • Jets are smaller than disks Total Disk Jet 230 GHz 345 GHz 230 GHz 345 GHz Final Exam

  33. mm-VLBI Predictions • Predict Gaussian size 36-41 μas • Shadow on Hawaii-Mexico or Mexico-Chile Shadow Final Exam

  34. Summary • Connect GRMHD simulations with observations • grtrans, geokerr (Dexter & Agol 2009) • Radiation edge of thick disks independent of spin for 15 degree tilt (Dexter & Fragile 2011) • Sgr A* (Dexter et al. 2009, 2010) • 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 • Disk/jet or jet models • Predict 36-41 μas size, shadow on Hawaii—Chile or Mexico—Chile • Robust results if geometry is correct Final Exam

  35. Future Work • Exciting times in BH astrophysics • Detailed models • Add polarization, complete sim sample • Make grtrans public • More speculative • Inhomogeneous disks & implications • Branch out: explosive astrophysics Final Exam

  36. Thanks! • Eric Agol & committee • Especially reading committee! • Chris Fragile, Omer Blaes & collaborators • My family & Kalista • Classmates • Astronomy department Final Exam

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

  38. Modeling M87 • Five(!) free parameters for fixed viewing geometry Final Exam

  39. Interferometry Morales & Wythe (2009) Final Exam

  40. Sgr A* VLBI • Largest angular size of any BH (w/ M87) • Microarcseconds; baby penguin on moon. • Very long baseline interferometry • High resolution: ~λ/D • Scattering: ~λ2 • Interferometry  Fourier transforms Final Exam

  41. Log-Normal Ring Models Final Exam

  42. 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 Final Exam

  43. Sagittarius A* Yuan et al (2003) Dodds-Eden et al (2009) Final Exam

  44. Constraining Models • Similar standard deviation to RIAF • Chile/Mexico are best bets for further constraining models • Significant constraint from simultaneous total flux at 345 GHz • Nice picture! 230 GHz 345 GHz Fish et al (2009) Dexter et al (2010) Final Exam

  45. 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 Final Exam L / LEdd

  46. 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 Final Exam L / LEdd

  47. Finite Speed of Light Toy emissivity, i=50 degrees 690 GHz, i=50 degrees Final Exam

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

  49. Light Curves Final Exam

  50. 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 Final Exam

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