The EVN

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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
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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

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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
  _at_ 128 Mbps

evn
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EVN capabilties

• Operates 3 4 weeks / year
• Uses MkIV recording system. Can observe at
  extremely high data rates 512 Mbits/sec
  SUSTAINED, gt 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.

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Resolution and Sensitivity

• Resolution of the EVN (in milliarcseconds).

Freq EVNMERLIN Full EVN Global VLBI
1.6 GHz 150-15 mas 5 mas 3.5 mas
5 GHz 50-4 mas 2 mas 1.2 mas
At 6 cm, the typical sensitivity of the full EVN
is around 20 microJy/beam in 10 hours.
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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

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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

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VLBI Facilities around the world
VLBA
CMVA VSOP
Australian LBA APT VERA
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• 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.

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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

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Radio jet and black hole physics - I

• Hong et al, 2002, in prep
• Multi-epoch VLBI (8), MERLIN(3) VLA(1)
  monitoring of blazar 1156295
• 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.

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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

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Radio source evolution

• EVN played a major role in identification of
  Compact Symmetric Objects (CSOs)
• Owsianik Conway (1998, AA, 337, 69) studied
  0710439, showed outer lobes moving apart at
  0.25c, lobes are separated by 90pc gt age of
  radio structure is 1100 yrs
• As CSOs grow it is presumed they evolve into
  classical double radio sources.
• Statistical studies under way

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Extragalactic H2O Megamasers
Galaxy Distance (Mpc) Flux (Jy) Galaxy Distance (Mpc) Flux (Jy)
NGC4945 3.7 4 IC2560 38 0.4
Circinus 4 4 NGC2639 44 0.2
NGC4258 7.3 4 NGC5793 50 0.4
M51 9.6 0.2 ESO 103-G35 53 0.7
NGC1386 12 0.9 Mrk 1210 54 0.2
NGC3079 16 6 ESO 103-G12 57 0.2
NGC1068 16 0.6 Mrk 348 63 0.04
NGC1052 20 0.3 Mrk 1 65 0.1
NGC5506 24 0.6 IC1481 83 0.4
NGC5347 32 0.1 NGC6240 98 0.03
NGC3735 36 0.2 IRAS F22265-1826 100 0.3
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Spectra of H2O masers

• Taxonomy
• Velocity-symmetry,
• Narrow-lines dominate
• Single emission feature
• Broad-hump dominates

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NGC4258 The archetypal accretion disk maser

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IC2560 a harder target(Ishihara et al, 2001,
PASJ)

• IC2560
• Confined mass 2.8 . 106 Msun
• Disk rotation rate 300 km/s

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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)

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25 years of Extragalactic H2O masers

• 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 lt 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.

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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.

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The archetypyal OHM Arp220

• Arp220, d76 Mpc
• Ultraluminous IR galaxy, Lfir gt 1012L?
• OH megamaser
• Double nucleus, tidal tails ? merger
• Extreme dust obscuration (Av1000)

Arp220 R-band, Hawaii
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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)

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• 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
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IIIZw35 another example

• EVNMERLIN Pihlstrom et al, 2001
• Ring of OH masers
• Possible detection of compact continuum
• Large velocity gradient in N component

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Stellar masers SiO
Diamond Kemball, 2002
TX Cam 88 weeks
Predominant motion is outflow Strong evidence for
shocks dominating the kinematics
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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
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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

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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 gt
B 1.1 mG
VX Sgr 1612 MHz MERLIN Szymczak et al
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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
• v1, v2, J1-0 (43 GHz) appear as expected with
  v2 lying closer to the exciting source
• v1, J2-1 (86 GHz) lies outside the 43 GHz
  masers, not known why
• Major VLBA proper motion programme underway

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Interstellar masers CH3OH EVN (Minier et al,
2001)
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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, AA) produced first dual
  polarization images of excited-state OH in W3(OH)
  at both 6031 and 6035 MHz gt signature of
  magnetic fields covering range 2 10 mG

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Gravitational Lenses

• JVAS B0218357 Biggs et al
• Global VLBI _at_ 8.4 GHz, resolution 1 mas
• Image A is stretched tangentially compared to B
• Instances of parity reversal visible
• Textbook case of gravitational lensing

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Supernovae
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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

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HI Absorption studies

• EVNVLBA observations of HI towards CSO 1946708
  (Peck Taylor, 2001)
• Indicate circumnuclear torus of neutral gas

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Future of EVN VLBI

• New telescopes (Yebes, SRT, FAST)
• Disc-based recording MkV / EVN PC-based system
  / Japan PC
• Routine gt 1 Gbps recording, no tape recorders
• Internet-based VLBI (e.g. Haystack e-VLBI
  workshop)
• iGRID2002 tests between JBO/WSRT -gt JIVE in Sept
  2002
• Geant -gt 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

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Post-2005
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e-MERLIN, LOFAR

• e-MERLIN funded fibre optic connection of 7
  MERLIN telescopes, 30 Gbps/telescope gt 10x
  sensitivity increase. Operational in 2007.

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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?

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The European VLBI Network