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Detection of the Intrinsic Size of Sagittarius A* with Closure Amplitude Imaging

Detection of the Intrinsic Size of Sagittarius A* with Closure Amplitude Imaging. Geoffrey C. Bower UC Berkeley. Team Closure. Backer, D.C. (UCB) Falcke, H. (MPIfR) Goss, W.M. (NRAO) Herrnstein, R. (CfA/Columbia) Zhao, J.-H. (CfA) Science , accepted. What We Want to See What We See.

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Detection of the Intrinsic Size of Sagittarius A* with Closure Amplitude Imaging

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  1. Detection of the Intrinsic Size of Sagittarius A* with Closure Amplitude Imaging Geoffrey C. Bower UC Berkeley

  2. Team Closure • Backer, D.C. (UCB) • Falcke, H. (MPIfR) • Goss, W.M. (NRAO) • Herrnstein, R. (CfA/Columbia) • Zhao, J.-H. (CfA) • Science, accepted

  3. What We Want to See What We See 7mm VLBA

  4. Scattering Inhibits Imaging &Points to Higher Frequencies Lo et al. 1998

  5. Difficulty of mm Imaging SgrA* • Axisymmetric Structure • Purely an amplitude measurement • Low Declination & High Frequency • Poor and variable antenna gain • Variable opacity • High Tsys • Short and variable coherence time • Lack of North-South resolution • Solution • Closure Amplitudes

  6. Closure Amplitude Properties • Independent of station-based gain errors • Still dependent on baseline-based errors • Decorrelation • Reduced sensitivity • 2/3 for N=7 • Non-Gaussian errors • Doeleman et al. 2000 --- 3mm imaging VmnVpq Cmnpq = ----------------- VmqVnp

  7. Data & Techniques • New and archival VLBA & VLA data • 10Q, 4K, 1U, 2X, 2C, 3L • Fringe-fit, form c.a. • Non-linear model-fitting of c.a. • Grid of models around best-fit solution to determine errors

  8. Results: 43 GHz Equal Scales

  9. New Results:Deviation from Scattering 10 Q, 4 K, 1 U, 2X, 2C, 3L experiments 0.3 cm 20 cm 0.3 cm 20 cm

  10. Alternatives • Errors in modeling • Monte Carlo simulations show we get what we put in • Phase decorrelation • No change in intrinsic size with 15-120 sec averaging time • Multiple components • Reduced chi^2 not improved • Refractive effects • Observations over a short span give larger 7mm size • Slope = 1.96 +/- 0.01 • Strongly inconsistent with scattering theory! • Weakly inconsistent with data

  11. Intrinsic Size • New scattering law derived • Major Axis • 24 +/- 2 Rs at 0.69 cm • Alpha_size = 1.6 +/- 0.2 • Flare in 1/9 Q band epochs: 60 +25 -15% • Minor Axis • 26 +/- 6 Rs at 0.69 cm < Lo et al size • Alpha_size= 2.2 +/- 0.5

  12. Intrinsic Size

  13. Emission/Accretion Implications • Axisymmetry? • Tb > 1010λ-1.2 K • Requires inhomogeneous models • Inconsistent with ADAF, single zone models • Jet • RIAF • Source comparable to Rs at 1.3mm • Physics in strong gravity • BH mass density • 4 x 104 Msun AU-3

  14. What’s Next? • Add GBT at 7mm • Links SC/HN to rest of array • Increased SNR for closure amplitude • 3mm • Model-dependent deconvolution

  15. The Future Meeting Friday after dinner

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