Sgr A* from General Relativistic MHD Simulations Jason Dexter University of Washington With Eric Agol, Chris Fragile and Jon McKinney

Galactic Center Black Hole AAS 217 Seattle2

Sagittarius A* AAS 217 Seattle3 Jet or nonthermal electrons far from BH Thermal electrons at BH Simultaneous IR/x-ray flares close to BH? no data available Charles Gammie

Millimeter VLBI of Sgr A* Precision black hole astrophysics 4AAS 217 Seattle Doeleman et al. (2008) Gaussian FWHM ~4 R s !

Black Hole Shadow Sensitive to details of accretion flow – Need accurate theoretical predictions! Bardeen (1973); Dexter & Agol (2009)Falcke, Melia & Agol (2000) 5AAS 217 Seattle

GRMHD Models of Sgr A* GRMHD perfect for mm Sgr A* – 3D, time-dependent, thick MRI- driven accretion flow (ADAF/RIAF) – Insignificant cooling(?) – Synchrotron radiation near BH Not perfect… – Collisionless plasma (mfp = 10 4 R s ) – Electrons AAS 217 Seattle6 Moscibrodzka et al. (2009)

Ray Tracing AAS 217 Seattle7 Fluid variables  emission at infinity Calculate light rays assuming geodesics. (ω >> ω p, ω c ) Observer camera: pixels are rays Intensities  Image, many frequencies  spectrum, many times  light curve  Schnittman et al. (2006)

Sgr A* Modeling Geodesics from geokerr (Dexter & Agol 2009) Time-dependent, relativistic rad. trans. Simulations from Fragile et al. (2007, 2009); McKinney & Blandford (2009) Joint fits to spectral (Marrone 2006), VLBI (Doeleman et al. 2008, Fish et al. 2010) data over grid in: – dM/dt, i, a, T i /T e AAS 217 Seattle8

GRMHD Fits to VLBI Data AAS 217 Seattle9 Dexter, Agol & Fragile (2009); Doeleman et al. (2008) i=10 degreesi=70 degrees  10,000 km   100 μas 

Parameter Estimates i = 60 degrees ξ = -70 degrees T e /10 10 K = 6 ± 2 dM/dt = 3 x M sun yr -1 All to 90% confidence CofC Colloquium Dexter et al. (2010, 2011) Sky Orientation Inclination Electron Temperature Accretion Rate All VLBI 2007

Millimeter Flares Correlation with accretion rate Not caused by magnetic reconnection Models reproduce observed mm flares AAS 217 Seattle11 Solid – 230 GHz Dotted – 690 GHz

Comparison to Observed Flares AAS 217 Seattle12 Eckart et al. (2008)Marrone et al. (2008)

Black Hole Shadow in Sgr A* AAS 217 Seattle13 Shadow may be detected on chile-lmt baseline Shadow

Additional Applications Tilted disks – Same variability, images, shadows – Precession: time-varying fit parameters? M87 – Can’t do “truncated” disk – All jet or mm disk AAS 217 Seattle14 Dexter, Agol & McKinney (2011) Dexter, Agol & Fragile (2011) Shadow

Conclusions Fit 3D GRMHD images/light curves of Sgr A* to mm VLBI observations Estimates of inclination, sky orientation agree with RIAF fits (Broderick et al. 2009, 2010) Electron temperature well constrained Reproduce observed mm flares LMT-Chile next best chance for observing shadow Future: polarized emission, complete set of sims. AAS 217 Seattle15

RIAF Fits AAS 217 Seattle16 Dexter et al. (2010, 2011), Broderick et al. (2010)

Spectra AAS 217 Seattle17

Visibility Variance AAS 217 Seattle18

Accretion Rate Variability AAS 217 Seattle19

Event Horizon Telescope AAS 217 Seattle20 UV coverage (Phase I: black) From Shep Doeleman’s Decadal Survey Report on the EHT Doeleman et al (2009)

Shadow in Closure Phase AAS 217 Seattle21