(sub)mm VLBI Science with ALMA MBH – paradigm, useful but dangerous, need to really push techniques to make MBH case solid. Shep Doeleman MIT Haystack Observatory Charlottesville, August 6-7 2009

Haystack Observatory

sub(mm)VLBI Science No scattering through ISM High Angular resolution (20micro arcsec) No scattering through ISM Enables observations with few Schwarzschild radius resolution for nearby AGN. Focus on SgrA*/M87: can observe strong-field GR effects. free fall rotating non- rotating orbiting GR Code 0.6mm VLBI 1.3mm VLBI

sub(mm)VLBI Progress Disk based Recorders: Mark5A, Mark5B, Mark5C Wideband VLBI Instrumentation: Disk based Recorders: Mark5A, Mark5B, Mark5C Digital Backends: DBE, DBE2/RDBE IF Converters Stable Frequency Standards: Modification of Hydrogen masers Exploration of alternative standards: Sapphire osc. Collaborations to bring new sub(mm) VLBI sites on line. JCMT, CSO, SMA, CARMA, ARO/SMT, IRAM, PdeB. ASTE, APEX, ALMA, S. Pole, LMT new sites (ATF). Phased array processor work: SAO. Logistics, Scheduling, Correlation, Analysis Techniques

mm/submm VLBI Collaboration MIT Haystack: 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 Harvard 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 Friberg UC Berkeley SSL: Dan Werthimer Caltech Submillimeter Observatory: Richard Chamberlain MPIfR: Thomas Krichbaum NRAO, NAOJ, ASIAA …

1.3mm Observations of SgrA* 908km 4030km 4630km Carried out 230GHz VLBI. 2. High resolution. 3. See through scattering 4. Design of experiment simple (3 baselines) and aimed at determining if there was structure on scales implicated by all light curve, vlbi, proper motion evidence already shown. These high freq obs make use of non-vlbi-facility instruments: have to create arrays using separate mm/submm facilities, but it can be done. days out of 5 possible (weather), 4Gb/s at each site, new Hydrogen maser at Mauna Kea and CARMA.

Determining the size of SgrA* OBS = 43as (+14, -8) SMT-CARMA INT = 37as (+16, -10) JCMT-CARMA SMT-JCMT 1 Rsch = 10as Doeleman et al 2008

Caveat: Very Interesting Structures SMT-CARMA 14 Rsch (140as) JCMT-CARMA SMT-JCMT Gammie et al

April 2009: M87

sub(mm) VLBI System

IF Conversion

Polarizer Needed to convert LCP/RCP to Linear Polarization. Can use grooved dielectric or x-cut quartz (sapphire too). Anti reflection coating required for quartz.

Observing Frequency Must avoid CO absorption feature near CO(2-1) line!!

Media 4Gb/s = 44TByte/24hours 22TBytes if 50% duty cycle. $0.10/Gbyte: ~$1300 for 8TByte Module ($500/chassis) High Altitude can be an issue. VLBA uses pressurized container.

Correlation Currently use Mark4 correlator capable of 1Gb/s processing can handle 2Gb/s at half-speed. limited to 16 frequency channels on input: could possible modify DBE to provide 64MHz channels. Number of stations? Software correlation DiFX To correlate 7 antennas at 16Gb/s data rate in real time requires ~100 similar nodes. Issues: data input and data writing off to disk.

ALMA VLBI Top Level Block Diagram LO Gen Antenna Electronics Central Electronics H Maser Or CSO CVR ALMA Correlator Digital Backend  ALMA Monitor/Control Post Proc. Software VLBI Recorder VLBI Mode Phase/Delay Algorithms