Connecting Accretion Disk Simulations with Observations Part II: Ray Tracing Jason Dexter 10/9/2008

Treu Group Meeting 10/9/20082/14 One Slide Part I Summary Dramatic advances in theory (GRMHD) –More physics –Much more difficult 3D, high resolution  short run times No radiation, may not conserve energy Observations still use old models  Need for comparison!

Treu Group Meeting 10/9/20083/14 My research aims to connect contemporary accretion disk simulations with new observations via ray tracing.

Treu Group Meeting 10/9/20084/14 Ray Tracing Method for performing radiative transfer –Turn fluid variables in accretion flow into observed emission at infinity. –Radiative transfer equation  Path integral –Two parts: 1.Calculate light trajectories. 2.Solve radiative transfer equation along ray.

Treu Group Meeting 10/9/20085/14 Ray Tracing Assume light rays are geodesics. Photographic plate  constants of motion Trace backwards to ensure that all rays used make it to observer simultaneously. Integrate along portions of rays intersecting flow. Intensities  Image, many frequencies  spectrum, many times  light curve Schnittman et al (2006)

Treu Group Meeting 10/9/20086/14 New Geodesics Code Dexter & Agol (2008), submitted: –New fast code to compute photon trajectories around spinning black holes. –Includes time, azimuth dependence for the most part ignored previously. Ideal for GRMHD!

Treu Group Meeting 10/9/20087/14 Toy Ray Tracing Problems: Thin Disk Mapping of photographic plate to equatorial plane Image of Page & Thorne BH

Treu Group Meeting 10/9/20088/14 Toy Ray Tracing Problems: Thin Disk Line emissionHotspots

Treu Group Meeting 10/9/20089/14 Toy Ray Tracing Problems: Spherical Accretion Synchrotron spectrum comparison to Shapiro (1973): Including absorption:

Treu Group Meeting 10/9/200810/14 Tilted GRMHD “Tilted” GRMHD: Black hole spin axis not aligned with torus axis. Shows structure lacking in standard GRMHD. Observational signature of tilted disk? Collaborating with Chris Fragile, Omer Blaes Fragile et al (2007)

Treu Group Meeting 10/9/200811/14 Garbage Result First result looks like equivalent untilted image. Trash?Schnittman et al (2006)

Treu Group Meeting 10/9/200812/14 Computational Challenges Interpolation –Grid points don’t match geodesic points. –Potentially sharp gradients when geodesics intersect corners of fluid zones. Convergence –Try different interpolation schemes –Different geodesic resolutions Keeping things moving

Treu Group Meeting 10/9/200813/14 More physics! Add time-dependence –Light delays vary over flow –Interpolation between data sets Realistic emission models –Synchrotron –Compton scattering(?) Polarization –GR effects on polarization as well

Treu Group Meeting 10/9/200814/14 Applications Sgr A* –Compare simulated images from GRMHD to future VLBI measurements –Test strong field GR –Constraints from polarization calculations On possible emission/absorption mechanisms Accretion models themselves Iron lines, QPOs, flares, etc.