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 Wilson MIT Haystack: Sheperd Doeleman (PI), Alan Rogers, Alan Whitney, Mike Titus, Dan Smythe, Brian Corey, Roger Cappallo, Vincent Fish U. Arizona Steward Obs: Lucy Ziurys, Robert Freund CARMA: Dick Plambeck, Douglas Bock, Geoff Bower James Clerk Maxwell Telescope: Remo Tilanus, Per Friberg Caltech Submillimeter Observatory (CSO): Richard Chamberlin UC Berkeley SSL: Dan Werthimer, Vinayak Nagpal MPIfR: Thomas Krichbaum JHU - Applied Physics Labs: Greg Weaver Honeywell: 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 ) These show the central mass to be about 3.9x10 6 M ⊙ The mass density must be greater than 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 1.2x10 12 cm or 10 μas 3 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 ) These show the central mass to be about 3.9x10 6 M ⊙ The mass density must be greater than 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 1.2x10 12 cm or 10 μas 4 Evidence for a super massive black hole (SMBH) in Sgr A* Closest approach of stellar orbits is 45 AU = 560R sch VLBI can probe to a scale of about 3 R sch — 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 = 43  as (+14, -8)  INT = 37  as (+16, -10) (1 R sch = 10  as) Doeleman et al 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 = 43  as (+14, -8)  INT = 37  as (+16, -10) (1 R sch = 10  as) 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 Technical details omitted See poster by Primiani et al.

Please sit down before reading the next line in this . 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, GHz, ISM scattered

Closure Phases: Hawaii-CARMA-Chile Spin = 0.9 Hot-spot at ~ 6R g Period = 27 min. Simulated data

“The future’s so bright, I’ve gotta wear shades” (Timbuk3, 1986) The 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 43 GHz (7 mm) Walker et al More luminous class of AGN with more massive central BH Eg M87, half the apparent size of SgrA* (1000 x more massive)