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(sub)mm VLBI Science with ALMA

(sub)mm VLBI Science with ALMA. Shep Doeleman MIT Haystack Observatory Charlottesville, August 6-7 2009. Haystack Observatory. High Angular resolution (20micro arcsec) No scattering through ISM Enables observations with few Schwarzschild radius resolution for nearby AGN.

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(sub)mm VLBI Science with ALMA

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  1. (sub)mm VLBI Science with ALMA Shep Doeleman MIT Haystack Observatory Charlottesville, August 6-7 2009

  2. Haystack Observatory

  3. 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. sub(mm)VLBI Science free fall rotating non- rotating orbiting 0.6mm VLBI GR Code 1.3mm VLBI

  4. 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 sub(mm)VLBI Progress

  5. 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 …

  6. 1.3mm Observations of SgrA* 908km 4030km 4630km days out of 5 possible (weather), 4Gb/s at each site, new Hydrogen maser at Mauna Kea and CARMA.

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

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

  9. April 2009: M87

  10. sub(mm) VLBI System

  11. IF Conversion

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

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

  14. 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. Media

  15. 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. Correlation

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

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