An Event Horizon Telescope: (sub)mm VLBI of Sgr A* Shep Doeleman MIT Haystack Observatory.
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Transcript of An Event Horizon Telescope: (sub)mm VLBI of Sgr A* Shep Doeleman MIT Haystack Observatory.
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An Event Horizon Telescope:(sub)mm VLBI of Sgr A*
Shep Doeleman
MIT Haystack Observatory
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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
Baganoff et al 2001
Ghez et al 2005
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Resolving Rsch-scale structures
Spinning (a=1) Non-spinning (a=0)
FalckeMeliaAgol
• SgrA* has the largest apparent Schwarzschild radius of any BH candidate.
• Rsch = 10as• Shadow = 5.2 Rsch (non-spinning)
= 4.5 Rsch (maximally spinning)
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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
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Wideband VLBI Systems
• 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.
Digital Backend (DBE) Digital Recorder (Mark5)
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mm/submm VLBI CollaborationMIT Haystack: Alan Rogers, Alan Whitney, Mike Titus,
Dan Smythe, Brian Corey, Roger Cappallo, Vincent FishU. Arizona Steward Obs: Lucy Ziurys, Robert Freund CARMA: Dick Plambeck, Douglas Bock, Geoff BowerHarvard 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 FribergUC Berkeley SSL: Dan WerthimerCaltech Submillimeter Observatory: Richard ChamberlainMPIfR: Thomas KrichbaumASIAA: Makoto Inoue, Paul Ho
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1.3mm Observations of SgrA*
4630km
DAYS OBSERVING - April 2007
4030km
908km
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Determining the size of SgrA*
SMT-CARMA
SMT-JCMT
OBS = 43as (+14, -8)
INT = 37as (+16, -10)
OBS = θ INT2 +θSCAT
2
Doeleman et al 2008
1 Rsch = 10as
ρ =1023M e pc−3
JCMT-CARMA
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The minimum apparent size.Broderick & Loeb
Noble & Gammie
Event Horizon
Ra =3 3 Rsch R≤1.5Rsch
R / 1−Rsch / R R>1.5Rsch
⎧⎨⎪
⎩⎪
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Caveat: Very Interesting Structures
Gammie et al
14 R
sch
(1
as)
SMT-CARMA
SMT-JCMT
JCMT-CARMA
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But…April 2009 SgrA* Detections
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Adding ALMA
Adding Telescopes: RIAF example
Adding LMTHawaii, CARMA, SMT
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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.
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Hot Spot Model for SgrA* Flares
QuickTime™ and aFLIC Animation decompressorare needed to see this picture.
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Hot Spot Models (P=27min)
Spin=0, orbit = ISCO Spin=0.9, orbit = 2.5xISCO
Models: Broderick & Loeb230 GHz, ISM scattered
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Closure Phases: Hawaii-CARMA-Chile
Spin = 0.9Hot-spot at ~ 6Rg
Period = 27 min.
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Detecting Rsch Polarization Structures
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The Event Horizon Telescope
• 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.
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Adding Telescopes
Phase 1: 7 Telescopes Phase 2: 10 TelescopesPhase 3: 13 Telescopes
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Technical Elements of EHT• 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
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Hawaii Phased Array Success(CSO+JCMT+SMA)-CARMA
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Progression to an Image: 345GHz
GR Model 7 Stations 13 Stations
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Summary• 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 Telescopewill address fundamental questions of BH physics and space-time.
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A Unique Opportunity“Right object, right technique,
right time”