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The EVN & VLBI Science

The EVN & VLBI Science. P.J.Diamond Jodrell Bank Observatory. With assistance from Mike Garrett of JIVE and Lincoln Greenhill of CfA. Shanghai Astronomical Observatory 26 April 2002. Overview of this lecture…. Description of the EVN, its history and its capabilities JIVE

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The EVN & VLBI Science

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  1. The EVN & VLBI Science P.J.Diamond Jodrell Bank Observatory With assistance from Mike Garrett of JIVE and Lincoln Greenhill of CfA Shanghai Astronomical Observatory 26 April 2002

  2. Overview of this lecture…. • Description of the EVN, its history and its capabilities • JIVE • Discussion of other VLBI arrays, global VLBI • VLBI Science • The future of the EVN and VLBI • e-MERLIN, LOFAR

  3. EVN – history, capabilities • VLBI started in late 60s: experiments in Canada, USA, Soviet Union, Europe • Late 70s – early 80s: formation of networks to make VLBI available to a wider community. • 1980: EVN formed: • IRA, IT; MPIfR, DE; NFRA, NL; NRAL, UK; OSO, SE • Now includes 11 institutes + associates and affiliates • Policy set by Consortium Board of Directors • EVN PC rate proposals; TOG responsible for engineering • EVN currently has ~5 times collecting area of VLBA • At 1 Gbps is ~ 14 times more sensitive than VLBA @ 128 Mbps evn

  4. EVN capabilties • Operates 3 * 4 weeks / year • Uses MkIV recording system. Can observe at extremely high data rates – 512 Mbits/sec SUSTAINED, => VERY SENSITIVE. • Frequency coverage predominantly around UHF, 1.2-1.7, 5, 6.7 and 8 GHz. Has capability at 22 and 43 GHz. • Excellent uv-coverage; Baseline lengths range from 200 – 2200 km in Europe. Inclusion of UK MERLIN array adds even shorter baselines. Extension of baselines to 9000 km via Chinese telescopes.

  5. Resolution and Sensitivity • Resolution of the EVN (in milliarcseconds)…. At 6 cm, the typical sensitivity of the full EVN is around 20 microJy/beam in ~10 hours.

  6. Upgrades… • EVN is continually changing its capabilities through network wide and local institute upgrades: • WSRT upgrade • Noto surface improvement • Lovell Telescope resurfacing • Receiver upgrades • Frequency flexibility • New telescopes: • 40m Yebes – 2004 • 64m Sardinia – 2005

  7. April 7, 1999 : first image Joint Institute for VLBI in Europe • JIVE formed by the EVN in 1993 to build and operate the EVN Mk IV correlator and to provide central support for EVN users. • July 21, 1997 : first fringes

  8. VLBI Facilities around the world

  9. 10 identical, 25 meter antennas, full time array, operated by a single entity – NRAO. • Recording system – VLBA terminals/recorders. • Baselines of 200 - 8600 km – spread across continental USA [60 km baselines if VLA included] • Extensive frequency coverage: 0.3, 0.6,1.3-1.7, 2.3, 5, 8, 12-15, 22-24, 41-45, 80-96 GHz. • Resolution range: 20 milliarcsecond (0.3 GHz), 5 mas (1.7 GHz); 0.5 mas (15 GHz); 0.2 mas (43 GHz). • 86 GHz capability on 6 telescopes. Co-observes with CMVA. • Co-observes with EVN – Global VLBI.

  10. VLBI Science • Radio jet & Black hole physics • Radio source evolution • Astrometry • Galactic and extra-galactic Masers • Gravitational Lenses • SNR and GRB studies • Nearby and distant starburst galaxies • Nature of faint radio source population • HI absorption studies in AGN…

  11. Radio jet and black hole physics - I • Hong et al, 2002, in prep • Multi-epoch VLBI (8), MERLIN(3) & VLA(1) monitoring of blazar 1156+295 • VLBI reveals oscillatory jet at milliarcsec scale, after ~40 mas jet straightens. • MERLIN shows 2 arcsec straight jet, then 90o bend – strong polarization • High proper motion (~8c) detected • All data indicates the projection of a helical jet possibly originating from precessing BH or binary BH.

  12. 2.3 GHz • EVN+MERLIN observations of • 3C264 (Lara et al, 1999, ApJ) • Superb comparison with HST • Radio jet has same wavelength • as optical jet but higher amplitude • Disruption of radio jet at • point of impact with dust • ring 8.4 GHz Radio jet and black hole physics - II • Chen et al, 2001 (Chin. J. Astron. Astrophys) • Multi-frequency VLBI of NRAO150 • Highly one-sided jet • Identification of new, steep spectral index component

  13. Radio source evolution • EVN played a major role in identification of Compact Symmetric Objects (CSOs) • Owsianik & Conway (1998, A&A, 337, 69) studied 0710+439, showed outer lobes moving apart at 0.25c, lobes are separated by ~90pc => age of radio structure is ~1100 yrs • As CSOs grow it is presumed they evolve into classical double radio sources. • Statistical studies under way

  14. Extragalactic H2O Megamasers

  15. Spectra of H2O masers • Taxonomy • Velocity-symmetry, • Narrow-lines dominate • Single emission feature • Broad-hump dominates •

  16. Kagoya/Inoue Review Accretion Disk: Miyoshi et al. 95 Jet @ 4000Rs: Herrnstein et al. 97 Accelerations: Nakai et al. 95 Greenhill et al. 95 Bragg et al. 00 Distance±7%: Herrnstein et al. 99 NGC4258: The archetypal accretion disk maser •

  17. Nobeyama 45m IC2560: a harder target(Ishihara et al, 2001, PASJ) • IC2560: • Confined mass ~ 2.8 . 106 Msun • Disk rotation rate : 300 km/s

  18. Central Engine D~100 km/s + + Jet O.33 pc Jet-driven H2O Masers: NGC 1052 Might featureless broad lines con- stitute blends of narrow lines from entrained or shocked ambient material? (Claussen, Diamond & Braatz. 1998, ApJ) •

  19. A rare but astrophysically important phenomenon. Extragalactic H2O masers tag star-formation in nearby galaxies. Proper motion measurements make possible unique measurements (e.g., galaxy motions). But starburst systems need study. H2O masers mark 21+ AGN central engines Thin accretion disks, AGN dynamics on < 1 pc scales Entrained or shocked ambient material for jets Jets and NLR-type outflows Other ? H2O masers can identify otherwise obscured AGN, corroborating claims of (widespread?) undercounts. 25 years of Extragalactic H2O masers

  20. Darling & Giovanelli (2001) OH Megamasers (OHM) • Discovered by Baan et al (1982) with Arecibo while searching for OH absorption. • Until 1998 ~ 30 OHM known. • Arecibo upgrade has resulted in a host of new detections. • ALL OHM are associated with ULIRGs, ALL ULIRGs appear to be the result of galaxy mergers.

  21. MERLIN: 18cm continuum The archetypyal OHM: Arp220 • Arp220, d~76 Mpc • Ultraluminous IR galaxy, Lfir > 1012L • OH megamaser • Double nucleus, tidal tails  merger • Extreme dust obscuration (Av~1000) Arp220: R-band, Hawaii

  22. MERLIN continuum image Arp220 • OH megamasers associated with both nuclei • Global VLBI observations (17 telescopes in Europe and US, resolution ~3 milliarcsec) showed four compact emission regions (Londale et al, 1998)

  23. Masers Continuum point sources Megamaser + radio supernovae 150pc Lonsdale et al, 1998 Smith et al, 1998 Diamond et al, 2002 VLBI resolves ~97% of continuum … BUT VLBI continuum, phase-referenced to the OH megamaser showed ~12 sub-mJy point sources. We interpret them as: LUMINOUS RADIO SUPERNOVAE: rate of 0.2-0.4 RSN/year

  24. IIIZw35: another example • EVN+MERLIN : Pihlstrom et al, 2001 • Ring of OH masers • Possible detection of compact continuum • Large velocity gradient in N component

  25. Components in N, S, NE & W Component in E Stellar masers: SiO Diamond & Kemball, 2002 TX Cam: 88 weeks Predominant motion is outflow Strong evidence for shocks dominating the kinematics

  26. Stellar masers : SiO Tangential vectors confined to narrow inner edge of ring. Strong evidence of effects of shocks. Remarkable circular magnetic field structure. Origin unknown B ~ 5 G

  27. B~280mG (Vlemmings, Diamond & van Langevelde, 2001) Stellar masers: H2O • Proper motions of masers around stars relatively ‘undeveloped’ subject until the advent of the VLBA – Marvel & Diamond (2002, in prep) • B field measurements now possible. Values for several stars indicate B ~ few hundred mG

  28. Stellar masers: OH Polarization Polzn vectors tangential to circumstellar envelope. Linear polzn ~ 10-20% Structure favours a radial field – maybe we are viewing a dipole field end-on. Circular polarization => B ~ 1.1 mG VX Sgr: 1612 MHz MERLIN: Szymczak et al

  29. Interstellar masers: SiO Greenhill et al, 1999 Doeleman et al, 1999, 2001 • Not very common, few sources (c.f. 100s – 1000s stellar sources) • Orion – KL: X marks the spot  indicates biconical outflow • v=1, v=2, J=1-0 (43 GHz) appear as expected with v=2 lying closer to the exciting source • v=1, J=2-1 (86 GHz) liesoutsidethe 43 GHz masers, not known why • Major VLBA proper motion programme underway

  30. Interstellar masers : CH3OH: EVN (Minier et al, 2001)

  31. Unique capabilities of EVN • Receivers at 6GHz enable studies of excited-state OH and methanol masers in regions of star formation • Desmurs et al (1998, A&A) produced first dual polarization images of excited-state OH in W3(OH) at both 6031 and 6035 MHz => signature of magnetic fields covering range 2 – 10 mG

  32. A B Gravitational Lenses • JVAS B0218+357 Biggs et al • Global VLBI @ 8.4 GHz, resolution ~ 1 mas • Image A is stretched tangentially compared to B • Instances of parity reversal visible • Textbook case of gravitational lensing

  33. M82 Vexp ~ 9500 km/s Supernovae

  34. Nature of faint radio source population • Faintest radio sources ever detected using VLBI (Garrett et al, 2001) • EVN images of sources detected in HDF superimposed on deep optical image. • 3 detections are AGN • Further observations planned

  35. HI Absorption studies • EVN+VLBA observations of HI towards CSO 1946+708 (Peck & Taylor, 2001) • Indicate circumnuclear torus of neutral gas

  36. Future of EVN & VLBI • New telescopes (Yebes, SRT, FAST…) • Disc-based recording : MkV / EVN PC-based system / Japan PC • Routine > 1 Gbps recording, no tape recorders • Internet-based VLBI (e.g. Haystack e-VLBI workshop) • iGRID2002 tests between JBO/WSRT -> JIVE in Sept 2002 • Geant -> Global Terabit Research Network • Aim for routine 1 Gbps, ‘ready all the time’ VLBI by 2005/6 • VLBI with SKA – requires stations over thousands of kilometres

  37. eEVN: European VLBI Network Data processing centre 32 - 256 Gbps China USA 1-8 Gbps South Africa Post-2005

  38. LOFAR in the Netherlands • LOFAR: • Freq range: 10-250 MHz • Resolution: few arcsec • 13000 antenna sets • Beamformer/correlator • – 8 beams • < 16 Tbps data rate e-MERLIN, LOFAR • e-MERLIN funded : fibre optic connection of 7 MERLIN telescopes, 30 Gbps/telescope => 10x sensitivity increase. Operational in 2007.

  39. Summary • VLBI is beginning to observe objects observed in other wavebands e.g. HDF, star-formation regions, super-massive black-holes, gravitational lenses. • Upgrades making VLBI ever more sensitive. EVN capable of being 14 times more sensitive than VLBA. • Plans being laid for internet-based VLBI (Japanese already doing it). • Future is bright for EVN: • Broadband • Sensitive • Available all the time?

  40. The European VLBI Network

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