1 / 16

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.

shika
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related