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VLBI/e-VLBI. An Introduction for Networkers Tasso Tzioumis, ATNF, CSIRO. Outline. Caveat: A Basic introduction Not a review of the latest techniques and results Radio Interferometry & VLBI Why: Science with VLBI How: Technology e-VLBI: Impact. Radio Interferometry.

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vlbi e vlbi


An Introduction for


Tasso Tzioumis, ATNF, CSIRO

  • Caveat: A Basic introduction
    • Not a review of the latest techniques and results
  • Radio Interferometry & VLBI
  • Why: Science with VLBI
  • How: Technology
  • e-VLBI: Impact
radio interferometry
Radio Interferometry

Simple Interferometer

  • Baseline B: Distance between antennas
  • “Virtual” telescope of diameter B.cos  (projected baseline)
  • Fringe pattern provides information on structure and position of the radio source

Fringe Pattern

earth rotation aperture synthesis
Earth Rotation Aperture Synthesis

uv- diagram

  • Baseline length and orientation (as viewed from the source) changes as the Earth rotates  new information on source structure.
  • uv-diagram - an indicator of imaging “quality” of an array of antennas
    • more antennas  filled uv  better image fidelity
connected element arrays
Connected Element Arrays


  • Baselines up to 10s of kms
  • “Real-time” detections
  • Full-time operation


  • Baselines 5-200 kms
  • Radio-linked  “real-time” Operation
  • e-MERLIN - fibre links under construction


x New Norcia


Atmosphere gives 1" limit without corrections which are easiest in radio

Jupiter and Io as seen from Earth

1 arcmin 1 arcsec 0.05 arcsec 0.001 arcsec

Simulated with Galileo photo


Unique VLBI Science

Zooming in!

gravitational lensing
Gravitational lensing

Double-quasar 0957+561 - VLBA+EVN, 18cm


Einstein Ring


ngc 4258
NGC 4258
  • Galaxy with disk
  • Radio continuum jet
  • Jet on one side obscured
  • H2O masers
  • Continuum amplifies maser emission (in green)
  • Tangential to disk maser emission – faint red & blue spots at Keplerian(point mass) rotation
  • First real measurement of nuclear Black Hole mass
  • Add time dimension (4D): geometric distance!
    • Image courtesy: Lincoln Greenhill

Bartel et al

mira variable tx cam
Mira Variable TX Cam
  • 43 GHz SiO maser emission around a star
  • No continuum emission at all
  • Actually many frequencies with masers; composite
  • movie!
    • Image courtesy: Phil Diamond & Athol Kembal
  • X-ray binary
  • Precessing jets
  • 0.26c jet speed
  • Baryonic jets


Movie of VLBI


astrometry geodesy

10 cm

Baseline Length


Baseline transverse

10 cm

Astrometry & Geodesy
  • Fundamental reference frames
    • International Celestial Reference Frame (ICRF)
    • International Terrestrial Reference Frame (ITRF)
    • Earth rotation and orientation relative to inertial reference frame of distant quasars
  • Tectonic plate motions measured directly
  • Earth orientation data used in studies of Earth’s core and Earth/atmosphere interaction
  • General relativity tests
    • Solar bending significant over whole sky
sgr a the galactic centre
SGR A* - The Galactic Centre

Measures rotation of the Milky Way Galaxy

spacecraft navigation
Spacecraft Navigation
  • Astrometry relative to background radio sources
  • Can measure micro-arcsecond position differences
  • Huygens spacecraft at Titan:
    • January 2005, VLBI tracking
    • Determine probe position during descent
    • Accuracy ~1 km
    • Fringes detected but data still being reduced
how current systems
How? - current systems
  • Data recorded on tape or disk systems at < 1 Gbps
  • Transported (slow!) to correlator facilities
  • Data processing by correlator
e vlbi science impact
e-VLBI Science Impact
  • Real-time operation (cf ATCA, VLA,…)
    • Fast response to “targets of opportunity” like flaring or exploding stars
    • Monitoring of evolving events
    • Immediate assessment of results
  • Higher sensitivity from high data rates
    • imaging sources at the edge of the universe
    • Very high quality imaging
    • (very efficient way to increase sensitivity cf building larger antennas)
  • Support high data rates of processed data
    • Facilitate “wide-field” imaging
    • Utilise GRID computing?
    • Database “mining”
ska an e vlbi array
SKA - an e-VLBI array?


1Tbit/s data transport

requirement in inner array

100 Gbit/s data transport

requirement in outer array

operational impact
Operational Impact
  • Flexible scheduling
    • Fast response to astronomical events
  • Robust operation
    • Real-time performance monitoring
  • Immensely easier data transport
  • Remote antenna operation
  • Remote data analysis
  • Distribution of processed data to users

 Lower operating costs?

  • VLBI offers a unique look at the universe - a “zoom” camera
  • e-VLBI will revolutionise VLBI operations
  • e-VLBI will enhance VLBI sensitivity, response time and flexibility
  • SKA will be an e-VLBI array
  • Networking is the future for VLBI