1 / 31

Frequency Standards and VLBI: Observing an Event Horizon

Frequency Standards and VLBI: Observing an Event Horizon. Sheperd Doeleman MIT Haystack Observatory. mm/submm VLBI Collaboration. MIT Haystack : Alan Rogers, Alan Whitney, Mike Titus, Dan Smythe, Brian Corey, Roger Cappalo, Vincent Fish U. Arizona Steward Obs: Lucy Ziurys, Robert Freund

belita
Télécharger la présentation

Frequency Standards and VLBI: Observing an Event Horizon

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. Frequency Standards and VLBI: Observing an Event Horizon Sheperd Doeleman MIT Haystack Observatory

  2. mm/submm VLBI Collaboration MIT Haystack: Alan Rogers, Alan Whitney, Mike Titus, Dan Smythe, Brian Corey, Roger Cappalo, Vincent Fish U. Arizona Steward Obs: Lucy Ziurys, Robert Freund CARMA: Dick Plambeck, Douglas Bock, Geoff Bower Harvard Smithsonian CfA: Jonathan Weintroub, Jim Moran, Ken Young, Dan Marrone, David Phillips, Ed Mattison, Paul Yamaguchi James Clerk Maxwell Telescope: Remo Tilanus, Per Friberg UC Berkeley SSL: Dan Werthimer Caltech Submillimeter Observatory: Richard Chamberlain MPIfR: Thomas Krichbaum JHU - Applied Physics Labs: Greg Weaver Honeywell: Irv Diegel

  3. The VLBI Technique /D (cm) ~ 0.5 mas /D (1.3mm) ~ 30 as

  4. VLBI Basics Earth Rotation Baseline Coverage Interferometer F T • Map must be real valued • Usually most of map is blank • Visibilities Map • Sparsely Sampled

  5. Averaging over Time and Frequency  Frequency  Time

  6. Atmospheric De-coherence From Moran & Dhawan 1995

  7. ALMA VLBI Coherence Tcoh ~ 4sec Tcoh ~ 10sec Tcoh ~ 35sec

  8. H-Maser/CSO Comparison Costa et al 1991

  9. Cryogenic Sapphire Osc for VLBI UWA Metrology Group (Tobar et al)

  10. CSO A CSO VLBI Ref. locked to GPS CSO Control

  11. Centaurus A: Optical

  12. Centaurus A: Radio

  13. The VLBA 43 GHz M87 Movie First 11 Observations Beam: 0.43x0.21 mas 0.2mas = 0.016pc = 60Rs 1mas/yr = 0.25c Walker, Ly, Junor & Hardee 2008

  14. Central Mass M ~ 4x106 M Rsch = 10as SgrA* Proper Motion V < 15km/s

  15. 10000 20000 30000 Time offset (s) X-ray/NIR Flares: An Indirect Size VLT: Genzel et al 2003 ~17 min periodicity? Baganoff et al 2001 Rise time ~300s Light crossing = 12 Rsch

  16. What we really want: the ‘Shadow’ Falcke et al free fall rotating orbiting non- rotating 0.6mm VLBI GR Code 1.3mm VLBI SgrA* has the largest apparent Schwarzschild radius of any BH candidate. BUT… SgrA* scattered ~ 

  17. 1.3mm Observations of SgrA* 4500km Fringe Spacing = 55as : A Baseball on the Moon

  18. 14 Rsch (140as) Gammie et al Determining a Size (Caveat) FWHM = 3.7 Rsch

  19. Alternatives to a MBH Evaporation and Condensation Maoz 1998

  20. Broderick & Loeb The minimum apparent size. Event Horizon Noble & Gammie

  21. <= 1.3mm-VLBI • Number of antennas is limited. • More sensitive to weather. • More sensitive to phase noise in electronics and H-maser. • Time hard to get on mm-wave telescopes. • Calibration difficult: use closure relations

  22. Hot Spot Models (P=27min) 230 GHz, ISM scattered Models: Broderick & Loeb Spin=0.9, orbit = 2.5xISCO Spin=0, orbit = ISCO

  23. Closure Phases: Hawaii-CARMA-Chile Spin = 0.9 Hot-spot at ~ 6Rg Period = 27 min.

  24. Hot Spot Model (a=0, i=30) SMTO-Hawaii-CARMA, 8Gb/s, 230GHz, 10sec points

  25. 1.3mm VLBI confirms ~4Rsch diameter for SgrA* • Implies that SgrA* is offset from Black Hole. • submm VLBI is able to directly probe Event Horizon scales and trace time variable structure. • Move to 345/450GHz requires frequency standards with y() < 10-14 at 10s. • Exploring H-Maser alternatives and modifying H-masers for short-term stability. • Imaging/Modeling Event Horizon possible within ~5 years: new telescopes in Chile. • Spare frequency standards? Summary

  26. VLBI Fringes Atmospheric Turbulence GHz : Ionosphere >1 GHz: Troposphere

  27. Scattering towards SgrA* • Scattering size ~ l2 • Intrinsic Structure masked by scattering : need high frequencies. • Lack of observed scintillation of SgrA* at 0.8mm sets lower size limit : 2Rsch=12mas • Use high frequency VLBI : resolution increases but scattering descreases.

  28. Seeing Through the Scattering OBS deviates from scattering for cm INT  SCAT for mm INT 

  29. mm/submm VLBI plans • Phase up apertures on Mauna Kea and CARMA to increase SNR (x10). • Observe again on SMT-HI-CARMA triangle. • Within 2 years add 4th antenna (Chile or LMT). • Move to 345GHz and dual polarization. Connected element polarimetry results likely suffer from beam depolarization.

  30. In situ standard testing

More Related