1. VLBI/e-VLBI An Introduction for Networkers Tasso Tzioumis, ATNF, CSIRO

2. 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

3. 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

4. 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

5. Connected Element Arrays VLA • Baselines up to 10s of kms • “Real-time” detections • Full-time operation ATCA

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

7. VLBI Arrays

8. LBA x NTD x New Norcia

9. VSOP

10. Resolution 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

11. Why? Unique VLBI Science Zooming in!

12. Cen A

13. Active Galactic Nucleus Model Hercules A

14. 3C236

15. Superluminal motion

16. Wide-field Imaging - surveying

17. Gravitational lensing Double-quasar 0957+561 - VLBA+EVN, 18cm PKS1830-211 Einstein Ring MERLIN, 5cm

18. 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

19. M82 Starburst

20. SN1993J Bartel et al

21. 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

22. SS433 • X-ray binary • Precessing jets • 0.26c jet speed • Baryonic jets Model Movie of VLBI Observations

23. 10 cm Baseline Length 1984-1999 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

24. SGR A* - The Galactic Centre Measures rotation of the Milky Way Galaxy

25. 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

26. How? - current systems • Data recorded on tape or disk systems at < 1 Gbps • Transported (slow!) to correlator facilities • Data processing by correlator

27. VLBI Recorders - Mkx

28. LBA Disk system S2 VLBI Recorder

29. The Future e-VLBI

30. e-VLBI global data transport

31. 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”

32. SKA - an e-VLBI array? SKA 1Tbit/s data transport requirement in inner array 100 Gbit/s data transport requirement in outer array

33. 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?

34. Summary • 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

36. VLBA

37. The VLBA

38. EVN

39. Kx recorders