1. The Transient Universe: AY 250 Spring 2007 Sagittarius A* Geoff Bower

2. The Transient Universe: AY 250 Spring 2007 Why Study Sgr A*? “Unique Laboratory for Astrophysics” –We can get closer to this black hole than any other 1 mas ~ 100 R_g –Unprecedented multi-wavelength information Winds; young stars; stellar remnants; molecular, atomic, ionized gas Stellar proper motions, radial velocities (Genzel, Ghez) NIR and X-ray emission (Genzel, Ghez, Baganoff, etc.) –Template for other AGN and compact objects –Fundamental physics exploration

3. The Transient Universe: AY 250 Spring 2007 What We Don’t Know Yet Why is Sgr A* so underluminous? –L ~ 10 -9 L Edd Models degenerate –Inflow, outflow, jets, nonthermal emission How does Sgr A* relate to other AGN? Fundamental gravity Narayan & Quataert 2005

4. The Transient Universe: AY 250 Spring 2007 Stellar Orbits: M BH ~ 3 x 10 6 M sun Ghez 2004

5. The Transient Universe: AY 250 Spring 2007

6. Sgr A East & West 6cm VLA (Morris & Yusef-Zadeh)

7. The Transient Universe: AY 250 Spring 2007 7mm VLBA (Bower & Backer 1998) What We See What We Want to See

8. The Transient Universe: AY 250 Spring 2007 Flux Density Variations: The Dog Wags its Tail

9. The Transient Universe: AY 250 Spring 2007 Radio Monitoring of Flux Density Macquart & Bower 2005

10. The Transient Universe: AY 250 Spring 2007 Power Spectral Analysis Zhao et al 1999Macquart & Bower 2005

11. The Transient Universe: AY 250 Spring 2007 Scintillation Drives Variability

12. The Transient Universe: AY 250 Spring 2007 X-Ray Flares Baganoff et al 2001

13. The Transient Universe: AY 250 Spring 2007 NIR Flares Genzel et al 2003

14. The Transient Universe: AY 250 Spring 2007 Simultaneous Radio/X-ray Flare 160x X-ray Flare

15. The Transient Universe: AY 250 Spring 2007 Simultaneous NIR/X-ray Flare Eckart et al 2004

16. The Transient Universe: AY 250 Spring 2007 Simultaneous NIR/X-ray Flare Eckart et al 2004 Small mm flare

17. The Transient Universe: AY 250 Spring 2007 July 2004 Radio/NIR/X-ray Flare

18. The Transient Universe: AY 250 Spring 2007 RadioSubmm InfraredX-ray nu Fnu Frequency Quiescent Flaring The Dog Wags Its Tail Particle heating Not Particle Injection

19. The Transient Universe: AY 250 Spring 2007 X-Ray Fluoresence No internal X-ray source Sgr A* or XRB origin 400 y ago 10^39 erg s^-1 Revnivtsev et al 2004 Hard X-rays 6.4 keV Fe Fluorescent line

20. The Transient Universe: AY 250 Spring 2007 X-Ray Fluoresence Changes in X-ray morphology in molecular cloud 14 pc in projection from Sgr A*  L~10^38 erg s^-1 –60 years ago –2-3 year duration Muno et al 2007

21. The Transient Universe: AY 250 Spring 2007 Linear Polarization: Unique Probe of Accretion and Jet Physics

22. The Transient Universe: AY 250 Spring 2007 No Linear Polarization

23. The Transient Universe: AY 250 Spring 2007 JCMT Discovery of Sgr A* Linear Polarization Detected at 150 – 690 GHz 850 um = 345 GHz 3.6 cm gray scale 90 deg angle flip Dust confusion an issue

24. The Transient Universe: AY 250 Spring 2007 BIMA Confirmation of Sgr A* Polarization

25. The Transient Universe: AY 250 Spring 2007 B N e RM < 2 x 10 6 10 Schwarzschild radii 10,000 Schwarzschild radii Polarized radiation propagates through dense, magnetized accretion region

26. The Transient Universe: AY 250 Spring 2007 MHD Simulations of Accretion Proga & Begelman 2003

27. The Transient Universe: AY 250 Spring 2007 Polarization Variability

28. The Transient Universe: AY 250 Spring 2007

29. Motion Around the Black Hole? Submm polarization 4 hours 13 Schwarzschild radii Marrone et al 2006

30. The Transient Universe: AY 250 Spring 2007 NIR Interferometry Paumard et al 2005 Microarcsec

31. The Transient Universe: AY 250 Spring 2007 Approaching the Event Horizon

32. The Transient Universe: AY 250 Spring 2007 The Black Hole Shadow Falcke, Melia & Agol 2000 Bardeen 1973

33. The Transient Universe: AY 250 Spring 2007 Event Horizon Shadow Shadow with radius 5 R_g must exist –Optically thin emission required Sgr A* is the most realistic candidate Black HoleShadow Diameter Sgr A*66 μ arcsec M8736 NGC 464924 Cen A10 SS 4330.00030

34. The Transient Universe: AY 250 Spring 2007 Angular Sizes 1.3 mm0.8 mm Intrinsic>66 μ arcsec>66 Scattering20 x 106 x 3 Beam (8000 km) 3020

35. The Transient Universe: AY 250 Spring 2007 Other Effects/Related Experiments Effects of black hole spin Polarization Imaging Phase-referenced imaging –Orbital period (Rs) ~ 20 minutes –How stable is the image? Temporal coherence due to lensing Broderick & Blandford 2004 Q V

36. The Transient Universe: AY 250 Spring 2007 Total Intensity Submm VLBI

37. The Transient Universe: AY 250 Spring 2007 Polarization Submm VLBI

38. The Transient Universe: AY 250 Spring 2007 Technical Requirements Global array High frequency receivers & antenna performance –230/350 GHz > Gigabit recording Phase stability –Water vapor radiometers Time standards Array Phasing –Correlator options Astrometry/Phase referenced observations eVLBI