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 Discussion of other VLBI arrays, global VLBI VLBI Science The future of the EVN and VLBI e-MERLIN, LOFAR

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

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.

Resolution and Sensitivity

• Resolution of the EVN (in milliarcseconds)….

Freq EVN+MERLIN Full EVN Global VLBI 1.6 GHz 5 GHz 150-15 mas 50-4 mas 5 mas 2 mas 3.5 mas 1.2 mas

At 6 cm, the typical sensitivity of the full EVN is

around

20 microJy/beam in ~10 hours.

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

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 • April 7, 1999 : first image

VLBI Facilities around the world

VLBA VSOP CMVA Australian LBA & APT VERA

• • • • • • • 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.

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…

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 90 o 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.

Radio jet and black hole physics - II

2.3 GHz 8.4 GHz •    Chen et al, 2001 (Chin. J. Astron. Astrophys) Multi-frequency VLBI of NRAO150 Highly one-sided jet Identification of new, steep spectral index component • 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

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

Galaxy NGC4945 Circinus NGC4258 M51 NGC1386 NGC3079 NGC1068 NGC1052 NGC5506 NGC5347 NGC3735

Extragalactic H

2

O Megamasers

12 16 16 20 3.7

4 7.3

9.6

24 32 36 Distance (Mpc) Flux (Jy) 4 4 4 0.2

0.9

6 0.6

0.3

0.6

0.1

0.2

Galaxy IC2560 NGC2639 NGC5793 ESO 103-G35 Mrk 1210 ESO 103-G12 Mrk 348 Mrk 1 IC1481 NGC6240 IRAS F22265-1826 38 44 50 53 54 57 63 65 83 98 100 Distance (Mpc) Flux (Jy) 0.4

0.2

0.4

0.7

0.2

0.2

0.04

0.1

0.4

0.03

0.3

Spectra of H

2

O masers

Taxonomy

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

NGC4258

4 3 2 1 0 -500 -300 500 1300 1500

NGC 4945

12 8 4 0 0.4

0.3

0.2

0.1

0.0

600 200 12 8 4 0 0 800 400 200 600 400 800 600 1000

Circinus

800 1000

NGC 1068

1000 1200 1400 1600

IRAS22265-1826

0.4

0.3

0.2

0.1

0.0

7200 7400 7600 7800 Heliocentric Velocity (km s 8000 -1 ) •

NGC4258: The archetypal accretion disk maser

Review Accretion Disk: Miyoshi et al. 95 Jet @ 4000R s : Herrnstein et al. 97 Accelerations: Nakai et al. 95

Greenhill et al. 95 Bragg et al. 00

Distance±7%: Herrnstein et al. 99 •

IC2560: a harder target

(Ishihara et al, 2001, PASJ)

Nobeyama 45m • IC2560:  Confined mass ~ 2.8 . 10 6 M sun  Disk rotation rate : 300 km/s

Jet-driven H

2

O Masers: NGC 1052

Central Engine

++

D ~100 km/s Might featureless broad lines con stitute blends of narrow lines from entrained or shocked ambient material?

Jet O.33 pc

(Claussen, Diamond & Braatz. 1998, ApJ)

•

25 years of Extragalactic H

2

O masers

• • • • A rare but astrophysically important phenomenon.

Extragalactic H 2 O masers tag star-formation in nearby galaxies.  Proper motion measurements make possible unique measurements (e.g., galaxy motions).

  H 2 O masers mark 21+ AGN central engines Thin accretion disks, AGN dynamics on < 1 pc scales  But starburst systems need study.

Entrained or shocked ambient material for jets   Jets and NLR-type outflows Other ?

H 2 O masers can identify otherwise obscured AGN, corroborating claims of (widespread?) undercounts.

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

appear to be the result of galaxy mergers.

ULIRGs

The archetypyal OHM: Arp220

• • • • • Arp220, d~76 Mpc Ultraluminous IR galaxy, L fir > 10 12 L  OH megamaser Double nucleus, tidal tails  merger Extreme dust obscuration (A v ~1000) MERLIN: 18cm continuum

Arp220: R-band, Hawaii

Arp220

MERLIN continuum image

• • 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)

Continuum point sources Megamaser + radio supernovae

150pc

Masers

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

IIIZw35: another example

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

Stellar masers: SiO

TX Cam: 88 weeks Diamond & Kemball, 2002 Predominant motion is outflow Strong evidence for shocks dominating the kinematics

Remarkable circular magnetic field structure. Origin unknown

Stellar masers : SiO

Tangential vectors confined to narrow inner edge of ring.

Strong evidence of effects of shocks.

B ~ 5 G

Stellar masers: H

2

O

• 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

B~280mG (Vlemmings, Diamond & van Langevelde, 2001)

Stellar masers: OH Polarization

VX Sgr: 1612 MHz MERLIN: Szymczak et al 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

Interstellar masers: SiO

• • • • • 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) lies

outside

the 43 GHz masers, not known why Major VLBA proper motion programme underway Greenhill et al, 1999 Doeleman et al, 1999, 2001

Interstellar masers : CH 3 OH: EVN (Minier et al, 2001)

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

Gravitational Lenses

A B • • • • • 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

Supernovae

M82 V exp ~ 9500 km/s

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

HI Absorption studies

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

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

eEVN: European VLBI Network

Data processing centre 32 - 256 Gbps USA 1-8 Gbps South Africa China

Post-2005

e-MERLIN, LOFAR

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

LOFAR in the Netherlands • LOFAR: • Freq range: 10-250 MHz • Resolution: few arcsec • 13000 antenna sets • Beamformer/correlator – 8 beams • < 16 Tbps data rate

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?

The European VLBI Network