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Phasing ALMA for VLBI: Building an Event Horizon Telescope

Phasing ALMA for VLBI: Building an Event Horizon Telescope. Big Questions. Is there an Event Horizon? Does GR hold near BH? How does matter accrete/outflow near a BH? Do Black Holes have spin? How do Black Holes launch jets? EHT addresses ASTRO 2010 questions and discovery areas:

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Phasing ALMA for VLBI: Building an Event Horizon Telescope

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  1. Phasing ALMA for VLBI:Building an Event Horizon Telescope

  2. Big Questions • Is there an Event Horizon? • Does GR hold near BH? • How does matter accrete/outflow near a BH? • Do Black Holes have spin? • How do Black Holes launch jets? • EHT addresses ASTRO 2010 questions and discovery areas: • How do black holes work and influence their surroundings? • What controls the mass-energy-chemical cycles within galaxies? • What are the connections between dark and luminous matter? • Time domain Astronomy.

  3. SgrA*: Best Case for a SMBH • Stellar orbits approaching within 45 AU. • Proper motions < 1km/s: M>10^5 Msol (Backer & Sramek 1999, Reid & Brunthaler 2004) • Short time scale X-ray flares (300 sec rise). • IF flares with modulation (a>0). Ghez et al 2005 VLT: Genzel et al 2003 Baganoff et al 2001

  4. 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 = 10μas • Shadow = 5.2 Rsch (non-spinning) = 4.5 Rsch (maximally spinning)

  5. Scattering towards the GC ISM Scattering: Θscat ~ λ2 Need to observe with VLBI at short wavelengths. Expected intrinsic size at 1.3mm is ~35 micro arcsec. 7mm: Bower et al 3mm: Shen et al

  6. 1.3mmλ Observations of SgrA* 908km 4030km 4630km Builds on long history of SgrA* VLBI and mmVLBI.

  7. SMT-JCMT SMT-CARMA Determining the size of SgrA* θOBS = 43μas (+14, -8) θINT = 37μas (+16, -10) JCMT-CARMA 1 Rsch = 10μas

  8. Alternatives to a MBH • Most condensations of smaller mass objects evaporate on short timescales. • Current obs imply Tevap<500 yrs. • Boson Star is a remaining ‘exotic’ possibility where R=Rsch + epsilon. • Depends on Boson mass. Proof of an Event Horizon? • If no EH, then the ‘surface’ will radiate inthe NIR, but none seen. (Broderick, Loeb, Narayan 2009)

  9. Constraining RIAF Models SgrA* 10-8 Eddington Inclination constrained to be >30 degrees: disk not ‘face-on’. Broderick, Fish, Doeleman & Loeb (2009)

  10. April 2009: SgrA* Flare on Rsch scales Fish et al, ApJL, v727, L36, 2011

  11. Tighter Constraints on BH spin. Broderick, Fish, Doeleman & Loeb, arXiv:1011.2770

  12. Time Variable Structures • Variabilty in NIR, x-ray, submm, radio. • VLBI caught SgrA* ‘before’ and ‘after’ flare. • Probe of metrics near BH, and of BH spin. • Requires non-imaging analysis. • Look for signatures of ‘hot spot’ flare models.

  13. Hot Spot Model for SgrA* Flares

  14. Tracing Black Hole Orbits with VLBI Steeger et al

  15. Measuring Black Hole Orbits with VLBI Spin = 0.9 Hot-spot at ~ 6Rg Period = 27 min.

  16. VLBA Movie of M87 @ 43 GHz (7 mm)Craig Walker et al. 2008 6.4 billion solar mass BH, FERMI & TeV source Beam: 0.43x0.21 mas 0.2mas = 0.016pc = 60Rs 1mas/yr = 0.25c

  17. Magnetically Driven Jets

  18. 1.3mmVLBI detection of M87: Jet Models a=0.998, =25deg Broderick & Loeb (2009) Gaussian size: 38 uas Rsch = 7.9 uas Shadow = 41 uas ISCO = 58 uas

  19. Building the Event Horizon TelescopeAstro2010 Roadmap Phase I • Adding Telescopes: 7 station array. • VLBI backends/recorders that support > 16Gb/s. • Central wideband correlator (up to 64Gb/s) [ATI prop]. • Phased Array processors (SMA, ALMA, PdeBure, CARMA) [MRI prop] • Leverage ALMA receivers for EHT [AAG prop]. • Procure Hydrogen Masers. • Recording media for 7-station 8Gb/s array • New site studies • Turn-key operations: remote operations • Project management, operations. • Endorsed by RMS Panel of US Decadal Review

  20. New (sub)mm VLBI Sites Current: ARO/SMT + CARMA + SMA + JCMT + CSO Phase 1: 7 Telescopes (+ IRAM, PdB, LMT, Chile/ALMA) Phase 2: 9 Telescopes (+ Spole, Haystack) Phase 3: 13 Telescopes (+ NZ, Africa,SEST)

  21. Progression to an Image GR Model 7 Stations 13 Stations

  22. Testing the No-Hair Theorem Johannsen & Psaltis 2009; Broderick et al • Test by perturbing quadrupole: Q’=-a2/M2 + e e=1 e=0 e=-1

  23. Phasing Arrays: SMA, CARMA this month. SMA: Weintroub, Primiani, et al CARMA: Wright, McMahon, Dexter, et al Text

  24. Phasing ALMA • Single most important objective for EHT. • Increases resolution by x2, sensitivity by x10. • Allows detection in 10s to all other EHT sites.

  25. ALMA Vitals • 64 x 12m dishes: 96m effective dish. • Excellent site • SEFD (1.3mm) ~ 100Jy • SEFD (3mm) ~ 70Jy • SEFD (7mm) ~ 40Jy • VLBA-ALMA baselines x10 sensitivity of single VLBA-VLBA baseline at 3mm. • N-S uv coverage to VLBA sites is roughly equivalent to VLBA_MK to VLBA_SC in length. 25

  26. Design for Real-time ALMA phasing 26

  27. Phasing ALMA on Science Targets • Use n(n-1)/2 baseline phases to solve for (n-1) antenna phases. • SNR for antenna phase: • With full BW in 10 sec: SNRa = 850 for SgrA* !! • Antenna solutions remain in high SNR regime for sources as faint as 100 mJy. • For fainter sources slew to phase calibrators.

  28. ALMA Phasing Timeline 2008-2010: Phasing Architecture designed in consultation with ALMA technical teams. Jan 2011: Endorsement by ALMA Board, MRI proposal submitted to NSF - anticipated start August 2011 2011-2013: New hardware (PIC - Fig 4) designed and fabricated, ALMA VLBI software functional, VLBI recorders installed. 2013-1014: Hydrogen maser installed, VLBI software complete, hardware tested, first VLBI observations with phased ALMA. 2014-2015: Commissioning and availability of ALMA phasing system to community.

  29. Non EHT Science with phased ALMA • M87: jet genesis, collimation - 3mm/7mm VLBI • AGN: polarization, pan-chromatic studies • SiO maser astrometry: • link IR-radio at Galactic Center • possible distance to LMC • Gravitational Lenses: central images • High resolution molecular absorption: • PKS 1830-211: isotopic abundances, evolution of fundamental constants • Use phased ALMA for pulsar/magnetar science. 29

  30. Event Horizon Telescope Collaboration MIT Haystack: Shep Doeleman, Alan Rogers, Vincent Fish, et al U. Arizona Steward Obs: Lucy Ziurys, Robert Freund, Dan Marrone Harvard CfA: Jonathan Weintroub, Jim Moran, Ray Blundell, et al CARMA: Dick Plambeck, Mel Wright, David Woody, Geoff Bower NRAO: John Webber, Ray Escoffier, Rich Lacasse Caltech Submillimeter Observatory: Richard Chamberlin UC Berkeley SSL: Dan Werthimer MPIfR: Thomas Krichbaum, Anton Zensus, Alan Roy, et al IRAM: Michael Bremer, Karl Schuster APEX: Karl Menten, Michael Lindqvist James Clerk Maxwell Telescope: Remo Tilanus, Per Friberg ASIAA: Paul Ho, Makoto Inoue NAOJ: Mareki Honma

  31. Summary • EHT results confirm Rsch structures in SgrA* and M87. • EHT has detected SgrA* closure phase and variability. • Technical path for Phase I of EHT clear. • Phasing ALMA transforms EHT within 3/4 years. • International team assembled for ALMA phasing project • Imaging an Event Horizon and observing BH orbits are within reach in <5 years. • Other phased array science enabled: lower frequency VLBI studies and pulsar/magnetar research.

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