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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

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Frequency Standards and VLBI: Observing an Event Horizon

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  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

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