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:• 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.

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).

VLT: Genzel et al 2003Baganoff et al 2001

Ghez et al 2005

Resolving Rsch-scale structures

Spinning (a=1) Non-spinning (a=0)

FalckeMeliaAgol

• SgrA* has the largest apparent Schwarzschild radius of any BH candidate.

• Rsch = 10μas• Shadow = 5.2 Rsch (non-spinning)

= 4.5 Rsch (maximally spinning)

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Scattering towards the GC

ISM Scattering:Θscat ~ λ

Need to observe withVLBI at short wavelengths.

Expected intrinsic size at 1.3mm is~35 micro arcsec.

7mm: Bower et al3mm: Shen et al

1.3mmλ Observations of SgrA*

4630km

4030km

908km

Builds on long history of SgrA* VLBI and mmVLBI.

Determining the size of SgrA*

SMT-CARMA

SMT-JCMT

θOBS = 43μas (+14, -8)

θINT = 37μas (+16, -10)

θOBS = θ INT2 +θSCAT

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1 Rsch = 10μas

ρ =1023M e pc−3

JCMT-CARMA

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)

Constraining RIAF Models

Broderick, Fish, Doeleman & Loeb (2009)

SgrA* 10-8 Eddington

Inclination constrainedto be >30 degrees: disk not ‘face-on’.

April 2009: SgrA* Flare on Rsch scales

Fish et al, ApJL, v727, L36, 2011

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Tighter Constraints on BH spin.

Broderick, Fish, Doeleman & Loeb, arXiv:1011.2770

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.

Hot Spot Model for SgrA* Flares

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Tracing Black Hole Orbits with VLBI

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Steeger et al

Measuring Black Hole Orbits with VLBI

Spin = 0.9Hot-spot at ~ 6Rg

Period = 27 min.

Beam: 0.43x0.21 mas 0.2mas = 0.016pc = 60Rs 1mas/yr = 0.25c

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VLBA Movie of M87 @ 43 GHz (7 mm)Craig Walker et al. 2008

6.4 billion solar mass BH, FERMI & TeV source

Magnetically driven jet launching ?Magnetically Driven Jets

1.3mmVLBI detection of M87: Jet Models

a=0.998, =25degBroderick & Loeb (2009)

Gaussian size: 38 uasRsch = 7.9 uasShadow = 41 uasISCO = 58 uas

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

New (sub)mm VLBI Sites

Current: ARO/SMT + CARMA + SMA + JCMT + CSOPhase 1: 7 Telescopes (+ IRAM, PdB, LMT, Chile/ALMA)Phase 2: 9 Telescopes (+ Spole, Haystack)Phase 3: 13 Telescopes (+ NZ, Africa,SEST)

Progression to an Image

GR Model 7 Stations 13 Stations

Testing the No-Hair Theorem• Test by perturbing quadrupole:

Q’=-a2/M2 + eJohannsen & Psaltis 2009; Broderick et al

e=1

e=0

e=-1

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Phasing Arrays: SMA, CARMA this month.

TextSMA: Weintroub, Primiani, et al

CARMA: Wright, McMahon, Dexter, et al

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

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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.

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Design for Real-time ALMA phasing

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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.

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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.

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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

Event Horizon Telescope Collaboration

MIT Haystack: Shep Doeleman, Alan Rogers, Vincent Fish, et alU. Arizona Steward Obs: Lucy Ziurys, Robert Freund, Dan MarroneHarvard CfA: Jonathan Weintroub, Jim Moran, Ray Blundell, et alCARMA: Dick Plambeck, Mel Wright, David Woody, Geoff BowerNRAO: John Webber, Ray Escoffier, Rich LacasseCaltech Submillimeter Observatory: Richard ChamberlinUC Berkeley SSL: Dan WerthimerMPIfR: Thomas Krichbaum, Anton Zensus, Alan Roy, et alIRAM: Michael Bremer, Karl SchusterAPEX: Karl Menten, Michael LindqvistJames Clerk Maxwell Telescope: Remo Tilanus, Per FribergASIAA: Paul Ho, Makoto InoueNAOJ: Mareki Honma

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.