VLBI with the SMA:The Event Horizon of SgrA* (& M87)

Jonathan Weintroub SMA/CfA

SMA Symposium, 15 April 2009

VLBI with the SMA:The Event Horizon of Sagittarius A*

Jonathan Weintroub SMA/CfA

SMA Symposium, 15 April 2009

Harvard Smithsonian CfA: Rurik Primiani, Jim Moran, Ken Young, Dan Marrone, David Phillips, Ed Mattison, Bob Vessot, Irwin Shapiro, Mark Gurwell, Ray Blundell, Rob Christensen, Bob WilsonMIT Haystack: Sheperd Doeleman (PI), 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 BowerJames Clerk Maxwell Telescope: Remo Tilanus, Per FribergCaltech Submillimeter Observatory (CSO): Richard Chamberlin UC Berkeley SSL: Dan Werthimer, Vinayak NagpalMPIfR: Thomas KrichbaumJHU - Applied Physics Labs: Greg WeaverHoneywell: Irv Diegel

•It is widely accepted that most galaxies have SMBHs at their centers

•Closest candidate is Sgr A* at the galactic center

•Measurements have been made of the orbits of a number of stars bound to Sgr A* with periods as short as 15 years at Keck and VLT using adaptive optics (Genzel et al., 2003, Ghez et al. 2005.)

•These show the central mass to be about 3.9x106

M⊙

•The mass density must be greater than 1022 M ⊙ pc-3

because lack of proper motion of Sgr A* means > 10% of the mass must be tied to Sgr A* (Reid and Brunthaler, 2004), which has size < 1AU .

•Most likely explanation: mass is in the form of a SMBH

•Schwarzschild radius is about 1.2x1012 cm or 10 μas3

Evidence for a super massive black hole (SMBH) in Sgr A*

This animation was created by Prof. Andrea Ghez and her research team at UCLA and is from data sets obtained with the W. M. Keck Telescopes.

•It is widely accepted that most galaxies have SMBHs at their centers

•Closest candidate is Sgr A* at the galactic center

•Measurements have been made of the orbits of a number of stars bound to Sgr A* with periods as short as 15 years at Keck and VLT using adaptive optics (Genzel et al., 2003, Ghez et al. 2005.)

•These show the central mass to be about 3.9x106

M⊙

•The mass density must be greater than 1022 M ⊙ pc-3

because lack of proper motion of Sgr A* means > 10% of the mass must be tied to Sgr A* (Reid and Brunthaler, 2004), which has size < 1AU .

•Most likely explanation: mass is in the form of a SMBH

•Schwarzschild radius is about 1.2x1012 cm or 10 μas4

Evidence for a super massive black hole (SMBH) in Sgr A*

•Closest approach of stellar orbits is 45 AU = 560Rsch

•VLBI can probe to a scale of about 3 Rsch—strong field GR

This animation was created by Prof. Andrea Ghez and her research team at UCLA and is from data sets obtained with the W. M. Keck Telescopes.

• Angular resolution is as fine as 20 μas (λ=0.8 mm on global baselines ~5000 km), several factors better than any other available technique in any waveband.

• Thus can resolve and image the structure of emission at the event horizon.

• The galactic center starts to become optically thin at λ~1 mm, and the emission peaks (3.5 Jy according to Marrone 2006, though the source is variable, of course)

• At longer wavelengths, the image is blurred by the turbulence of ionized gas (scattering λ∝ 2)

• In the optical Sgr A* is obscured by dust.

5

Submillimeter VLBI is uniquely suited to study Sgr A*

“The SMA will almost certainly take part in VLBI experiments at some stage . . .”

(Masson, 1996)

Determining the size of SgrA*

SMT-CARMA

SMT-JCMT

OBS = 43as (+14, -8)

INT = 37as (+16, -10)

(1 Rsch = 10as)Doeleman et al 2008

2007 1.3 mm VLBI observations confirm event-horizon-scale structures

Determining the size of SgrA*

SMT-CARMA

SMT-JCMT

Doeleman et al 2008

JCMT-CARMA(limit)

OBS = 43as (+14, -8)

INT = 37as (+16, -10)

(1 Rsch = 10as)

Falcke, Melia & Agol, 1999

Other structures are consistent with the measurement: e.g. a “shadow” in the emission

Submillimeter Valley, Mauna Kea, HI

Phased Array Processor Block Diagram

Development supported by CfA IR&D and REF funding

Technica

l details

omitted

See poster b

y Prim

iani et a

l.

Please sit down before reading the next line in this email.Attached are strong fringes between the CARMA C5 antenna and the phased array processor !!!!

(Mike Titus, 7 April 2009)

Weaker phased array fringes on 3C273

(strongest calibrator in 2007)

Hot Spot Models (P=27min)

Spin=0, orbit = ISCO Spin=0.9, orbit = 2.5xISCO

Models: Broderick & Loeb, 2008

230 GHz, ISM scattered

Closure Phases: Hawaii-CARMA-Chile

Spin = 0.9Hot-spot at ~ 6Rg

Period = 27 min.Simulated data

“The future’s so bright, I’ve gotta wear shades”(Timbuk3, 1986)

• The 2007 1.3 mm results are significant in and of themselves. Further, they show that submillimeter VLBI can probe SgrA* on event-horizon scales

• The 2009 VLBI campaign was completed just last week. We already have detections validating the Phased Array.

• The SMA is now the center of submillimeter VLBI on Mauna Kea, a key site for the “Event Horizon Telescope”

• The emergence of ALMA enhances, rather than diminishes, the SMA’s role in the global VLBI array

• SgrA* and M87 data both gathered in 2009, results pending

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

More luminous class of AGN with more massive central BHEg M87, half the apparent size of SgrA* (1000 x more massive)