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

8. Proof of an Event Horizon?
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.
m87 is largest MBH candidate, but enclosed mass poorly constrained.
Proof of an Event Horizon?
If no EH, then the ‘surface’ will radiate in the 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:

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 mas = 0.016pc = 60Rs mas/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 Telescope Astro2010 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
Test by perturbing quadrupole: Q’=-a2/M2 + e
Johannsen & Psaltis 2009; Broderick et al
e=1
e=0
e=-1

23. Phasing Arrays: SMA, CARMA this month.
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 phasing26

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
: Phasing Architecture designed in consultation with ALMA technical teams.
Jan 2011: Endorsement by ALMA Board, MRI proposal submitted to NSF - anticipated start August 2011
: New hardware (PIC - Fig 4) designed and fabricated, ALMA VLBI software functional, VLBI recorders installed.
: Hydrogen maser installed, VLBI software complete, hardware tested, first VLBI observations with phased ALMA.
: 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 : 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.