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An Event Horizon Telescope: (sub)mm VLBI of Sgr A*

An Event Horizon Telescope: (sub)mm VLBI of Sgr A*. Shep Doeleman MIT Haystack Observatory. SgrA*: Best Case for a SMBH. Stellar orbits within 45 AU: M~4x10 6 Msol Proper motions < 1km/s: M>10^5 Msol (Backer & Sramek, Reid & Brunthaler) Submm/NIR/X-ray flares variability.

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An Event Horizon Telescope: (sub)mm VLBI of Sgr A*

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  1. An Event Horizon Telescope:(sub)mm VLBI of Sgr A* Shep Doeleman MIT Haystack Observatory

  2. SgrA*: Best Case for a SMBH • Stellar orbits within 45 AU: M~4x106 Msol • Proper motions < 1km/s: M>10^5 Msol (Backer & Sramek, Reid & Brunthaler) • Submm/NIR/X-ray flares variability. VLT: Genzel et al 2003 Ghez et al 2005 Baganoff et al 2001

  3. Resolving Rsch-scale structures Falcke Melia Agol Spinning (a=1) Non-spinning (a=0) • SgrA* has the largest apparent Schwarzschild radius of any BH candidate. • Rsch = 10as • Shadow = 5.2 Rsch (non-spinning) = 4.5 Rsch (maximally spinning)

  4. High Frequency VLBI Resolution: /D (cm) ~ 0.5 mas /D (1.3mm) ~ 30 as /D (0.8mm) ~ 20 as ISM Scattering: scat ~  Can’t use VLBA Short  Challenges: Weather, freq. stnds, electronics noise Increased Sensitivity

  5. Wideband VLBI Systems Digital Recorder (Mark5) Digital Backend (DBE) • Total cost $40-50K per station. • x16 in BW over current VLBA sustainable rates. • Equivalent to replacing VLBA with 50m antennas. • Used for VLBA upgrade: x4 in sensitivity over current VLBA sustainable rate.

  6. mm/submm VLBI Collaboration MIT Haystack: Alan Rogers, Alan Whitney, Mike Titus, Dan Smythe, Brian Corey, Roger Cappallo, 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, Bob Vessot, Irwin Shapiro, Mark Gurwell, Ray Blundell, Bob Wilson James Clerk Maxwell Telescope: Remo Tilanus, Per Friberg UC Berkeley SSL: Dan Werthimer Caltech Submillimeter Observatory: Richard Chamberlain MPIfR: Thomas Krichbaum ASIAA: Makoto Inoue, Paul Ho

  7. 1.3mm Observations of SgrA* 908km 4030km 4630km DAYS OBSERVING - April 2007

  8. SMT-CARMA SMT-JCMT Determining the size of SgrA* OBS = 43as (+14, -8) INT = 37as (+16, -10) JCMT-CARMA 1 Rsch = 10as Doeleman et al 2008

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

  10. SMT-CARMA SMT-JCMT Caveat: Very Interesting Structures 14 Rsch (140as) JCMT-CARMA Gammie et al

  11. But…April 2009 SgrA* Detections

  12. Adding ALMA Hawaii, CARMA, SMT Adding LMT Adding Telescopes: RIAF example

  13. Time Variable Structures • Variabilty in NIR, x-ray, submm, radio. • Probe of metrics near BH, and of BH spin. • Violates Earth Rotation aperture synthesis. • Use ‘good’ closure observables to probe structure as function of time.

  14. Hot Spot Model for SgrA* Flares

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

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

  17. Detecting Rsch Polarization Structures

  18. An international collaborative project assemble a global submm-VLBI array for observing and resolving Event Horizons. • Key observations have removed scientific uncertainty (i.e. will we see anything?). • Technical Elements: low risk extensions of ongoing efforts and leveraging investments from ALMA and other development projects. • Collaboration: necessarily a international project using many facilities. • Strong element of training at intersection of submm science and interferometry. The Event Horizon Telescope

  19. Adding Telescopes Phase 1: 7 Telescopes Phase 2: 10 Telescopes Phase 3: 13 Telescopes

  20. ALMA quality, dual pol rx and LO for all sites. • Testing hardware for in-situ verification. • Central correlation facility. • VLBI backends/recorders at rates up to 64Gb/s • Phased Array processors (ALMA, PdeBure, CARMA, Hawaii) • Low noise freq. references. • Logistics/Observations/Project Management Technical Elements of EHT

  21. Hawaii Phased Array Success(CSO+JCMT+SMA)-CARMA

  22. Progression to an Image: 345GHz GR Model 7 Stations 13 Stations

  23. 1.3mm VLBI confirms ~4Rsch diameter for SgrA* • Non-Imaging VLBI can extract BH parameters. • Imaging soon possible with EHT developments. • Increased sensitivity enables submm VLBI to directly probe Event Horizon scales and trace time variable structure (complements GRAVITY, IXO). • Over the next decade: • A VLBI Event Horizon Telescope • will address fundamental questions of BH physics and space-time. Summary

  24. A Unique Opportunity“Right object, right technique, right time”

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