Everything%20you%20wanted%20to%20know%20about%20(e-)VLBI

1
Everything you wanted to know about (e-)VLBI
and more

• Zsolt Paragi, JIVE

2
Abstract

• I will talk briefly about the Very Long Baseline
  Interferometry (VLBI) technique and what we can
  do with it. The European VLBI Network (EVN) will
  be shortly introduced. Then I will describe
• the recent e-VLBI developments at JIVE. Science
  examples will be mixed in all over the talk. The
  following 30 minutes will be about
• RESOLUTION
• 
  SENSITIVITY
• RAPID RESPONSE
  SCIENCE

3
Resolution ? 1.22?/D
This translates to about an arcminute or more
even with the great, 100m Effelsberg radio
telescope at cm wavelengths.
4
Very Long Baseline Interferometry (VLBI) (Long
long time ago, in a far away galaxy)

• Data recorded on mag-
• netic tapes
• Later processed in a
• correlator
• This need thorough
• knowledge of geometry
• and very precise timing
• information
• Earth diameter limits
• resolution (tipically mas)
• Number of telescopes,
• their diameter and
• performance, as well as
• the recording rate limits
• the sensitivity
• Magnetic tapes could do
• 256 Mbps (512 with two
• heads)

5
Fringes
001011101010011001010001 100101111001011101010011
6

• An interferometer measures the
  Fourier-components of the sky brightness
  distribution
• As the Earth rotates, the projected baselines
  sample various spatial frequencies, that
• provide information on the target source
  structure at various angular scales

• We measure the fringe phase
• and amplitude at each of these
• sampled spatial frequencies
• The data are pre-processed,
• and a dirty image is formed
• by Fourier transform
• Further calibration of fringe
• amplitudes and phases is done
• parallel to the deconvolution
• of this dirty image

7
And what can I do with this?

• Objects with fairly compact structures and
• astrometry studies
• e.g. parallax measurements up to several kpc
• (? lt 0.001 arcsecond)
• may resolve nearby stars and their environment,
• (0.1 AU resolution at 100 pc)
• Active Galactic Nuclei, (compact jets of several
• pc have mas structures at even high redshifts)
• black hole astrophysics, gravitational lenses
  and
• much more
• Geodetic VLBI tectonics on Earth, time service
• end EOPs, International Celestial Reference
• Frame (ICRF)

And of course spectral line observations of HI,
and MASERs of stellar and extragalactic origin.
NGC4258 Miyoshi et al. (1995), Nature 373, 127
8
VLBI networks
VLBA
VERA
9
The European VLBI Network

• Some of the worlds greatest radio telescopes,
  e.g. Effelsberg 100m, Lovell 76m telescopes,
• Westerbork Synthesis Radio Telescope
• Outside Europe includes Hartebeesthoek (South
  Africa), Urumqi and Shanghai (China)
• Several telescopes are being built that will
  join the EVN Yebes 40m (this year), telescopes
• in Sardinia, Latvia, Ireland and China
• Operating in three observing sessions per year,
  sometimes jointly with MERLIN (UK) and
• the VLBA (USA) global VLBI
• Observing wavelength ranges from 92cm to 1.3cm
• The most sensitive standalone VLBI array (the
  so-called High Sensitivity Array formed
• occasionally by the VLBA, VLA, GBT and maybe
  Arecibo competes with it)
• The data are correlated in the EVN MkIV
  correlator at JIVE

http//www.evlbi.org/ http//www.jive.nl/
10
The end of the tape era

• Tape recording had limited performance (parity
• errors), and
• limited data rate (256 Mbps 512 Mbps with
• two write heads).
• Tapes were expensive
• Tape playback units were not easy to maintain

• Disk based recording systems were developed at
• Haystack (Mark5A) and Metsahovi Radio
• Observatory (PC EVN)
• And it worked!
• The EVN is fully disk operational (Mark5A)
• since early 2004
• Cheaper, off the shelf technology, perfect
• recording data rate up to 1 Gbps
• http//www.haystack.edu/tech/vlbi/mark5/

11
Just a flavour of what is possible SNR in M82 1
sigma noise 15 ?Jy/beam (limited by the noisy
host galaxy)
Paragi et al. (in prep.)
MERLIN archive 1.6 GHz data, 1997
12
The sensitivity
For six hours on-source integration in the C-band
(6cm) the theoretical 1 sigma rms noises
are VLBA, 128 Mbps 80 ?Jy/beam HSA
(VLBAVLA27GBT), 128 Mbps 18 ?Jy/beam Full
EVN, 1 Gbps 8 ?Jy/beam Another example why
the sensitivity limits are pushed so hard
Predicted radio flux densities of ULXs
in nearby galaxies, if these are powered
by IMBHs
Paragi et al. (2006)
13
The reliability

• Disk recording is better quality, but it
• also provides a way to quickly check
• telescope performance ftp tests
• 2-4s data at 256 Mbps ? 64-128 MB files,
• may be transferred through the Internet!
• Data processed by a software correlator
• developed in NICT, Japan

• Since late 2004 there are regular ftp tests
• during EVN sessions.
• The software correlator runs on a PC cluster
• Feedback to telescopes used to take at least
• a week, now it is a matter of minutes
• OK, let us see what else can we improve

14
VLBI observations timeline
1-2 weeks 2-3 months
2-3 months
Select your source
Write an observing proposal
EVN PC makes a decision
EVN scheduler provides a date
?
?
?
another 2-3 months well, why would you
hurry?
Publishing results
Observe with VLBI
Data correlation
Data processing
?
?
?
THIS MUST CHANGE!
15
Target of Opportunity projects
An example the huge flare of SGR1806-20

• SGR1806-20 is a soft gamma-ray repeater a
• neutron star with very strong magnetic fields,
• a magnetar
• Produced the greatest explosion witnessed by
• humans in our Galaxy, on 27 December 2004
• Observations with various instruments, also
• VLBI (with the VLBA array)
• Could not image reliably because of lack of
• known calibrator in the vicinity of the target!
• Is there a way to do these projects more
  efficiently?
• Is there a way to get the data and analyze them
• quickly???

Fender et al. (2005), MNRAS 367, L6
16
e-VLBI Proof-of-Concept Project (long, long time
ago)

• DANTE/GÉANT Pan-European Network
• SURFnet Dutch NREN
• GARR Italian NREN
• UKERNA UK NREN
• PSNC Polish NREN
• DFN German NREN
• KTHNOC/NORDUnet Nordic NREN
• Manchester University Network application
  software
• JIVE EVN Correlator
• Westerbork telescope Netherlands
• Onsala Space Observatory Sweden
• MRO Finland
• MPIfR Germany
• Jodrell Bank UK
• TCfA Poland
• CNR IRA Italy

17
(No Transcript)
18
Network Topology for eVLBI
Gbit link
Chalmers University of Technology, Gothenburg
Network North-West
OnsalaSweden
Gbit link
TorunPoland
150Mbit link
Jodrell BankUK
WesterborkNetherlands
DedicatedGbit link
MERLIN Microwave link
Dwingeloo DWDM link
CambridgeUK
MedicinaItaly
19
The beginning of e-VLBI in Europe

• With e-VLBI one could continuously monitor
  telescope performance
• Results would be available almost immediately
• Could be more flexible to ToO projects
• May make quick decisions about the use of a
  calibrator, or follow-up observations
• The EVN would be more competent in hot topic
  science
• Had to prove that the EVN MkIV correlator can be
  upgraded to realtime operations
• Had to prove that the research networks can cope
  with the network load
• Had to test and tune transfer protocols
• First tests were promising, and then came the
  first real e-VLBI image in 2004

20
The first e-VLBI science result (line, 32 Mbps)
e-VLBI, September 2004
MERLIN, March 2002
IRC10420 Richards et al. (2004)
21
The first e-VLBI science result (continuum)

• SN2001em was discovered on 15 September 2001 in
  UGC11794 galaxy (Pepenkova 2001).
• Redshift z0.02 corresponding to a distance of
  80Mpc.
• Filippenko and Chornok (2001) classified it as
  type Ib/c, most likely Ic.
• Exceptional radio and X-ray luminosities
• (off axis GRB, developing late radio emission
• due to jet break?),
• Not quite a 1 mJy radio source
• EVN observations Cm, Jb2, On, Tr, Wb (128Mbps),
  Arecibo 300m (64 Mbps)
• at 18cm, on 2005 Mar 11
• Tentative detection (4.5 ?) of the first real
  faint target with e-VLBI
• Paragi et al. (2005), MSAIt 76, 570

22
What is EXPReS?

• EXPReS Express Production Real-time e-VLBI
  Service
• Three year project, started March 2006, funded by
  the European Commission (DG-INFSO), Sixth
  Framework Programme, Contract 026642
• Objective to create a distributed, large-scale
  astronomical instrument of continental and
  inter-continental dimensions
• Means high-speed communication networks
  operating in real-time and connecting some of the
  largest and most sensitive radio telescopes on
  the planet
• http//www.expres-eu.org/

23
EXPReS Partners

• Joint Institute for VLBI in Europe (coordinator)
• AARNET Pty Ltd., Australia
• ASTRON, The Netherlands
• Centro Nacional de Informacion Geografica, Spain
• Chalmers Tekniska Hoegskola Aktiebolag, Sweden
• Commonwealth Scientific and Industrial Research
  Organization (CSIRO), Australia
• Cornell University, USA
• Delivery of Advanced Network Technology to Europe
  Ltd. (DANTE), UK
• Instituto Nazionale di Astrofisica, Italy
• Instytut Chemii Bioorganicznej PAN, Poland
• Max Planck Gesellschaft zur Foerderung der
  Wissenschaften e.V., Germany
• National Research Foundation, South Africa
• Shanghai Astronomical Observatory, Chinese
  Academy of Sciences, China
• SURFNet b.v., The Netherlands
• Teknillinen Korkeakoulu, Finland
• The University of Manchester, UK
• Universidad de Concepcion, Chile
• Uniwersytet Mikolaja Kopernika, Poland
• Ventspils Augstskola, Latvia

24
Telescope sites participating

• Image courtesy of Dr. Francisco Colomer

25
Activities

• Description Leader
• PC Project Coordinator Michael Garrett, JIVE
• NA1 Management of I3 T. Charles Yun, JIVE
• NA2 EVN-NREN Forum John Chevers, DANTE
• NA3 eVLBI Science Forum John Conway, Chalmers
• NA4 Public Outreach Kristine Yun, JIVE
• SA1 Production Services Arpad Szomoru, JIVE
• SA2 Network Provisioning Francisco Colomer,
  CNIG-IGN
• JRA1 FABRIC Huib Jan van Langevelde, JIVE

26
Telescopes connections (early 2007)
Soon available Effelsberg, Yebes 40m, Shanghai
27
e-VLBI activities in 2006

• There are regular e-VLBI test observations in
  every six week (on average)
• Normal operations at 256 Mbps (Cm, Jb2, Mc, On,
  Tr, Wb)
• Fringes to several telescopes at 512 Mbps, most
  recently to Mc
• 24h time is pre-allocated for science
  observation during each e-VLBI test
• Observing proposals may be submitted two weeks
  before the advertised date
• More info at http//www.evlbi.org/evlbi/evlbi.htm
  l
• Science projects observed in 2006
• Cyg X-3, 20 Apr/18 May, 128 Mbps, Tudose et al.
• GRS1915, 20 Apr, 128 Mbps, Rushton et al.
• LSI 61.303, 256 Mbps, 26 Oct, Perez-Torres et
  al.
• Algol, 26 Oct/14 Dec, 256 Mbps, Paragi et al.
• Calibrators near M81, 14 Dec, 256 Mbps,
  Brunthaler et al.
• INTEGRAL microquasar candidates, 14 Dec, Pandey
  et al.

28
First refereed journal papers
Rushton et al. (2007), MNRAS 374, L47 Tudose et
al. (2007), MNRAS very soon
Cyg X-3
29
Want to propose e-VLBI observations?

• e-VLBI proposals must be submitted by e-mail to
  the EVN PC a web proposal
• tool will be available in a couple of days
• e-VLBI proposals are just like other EVN
  proposals, but you must take additional care to
• justify properly why urgency is needed (target
  of opportunity, e.g. known transient flares,
• or need to check calibrators quickly for
  another project, taking part in an observational
• campagin)
• give accurate coordinates (sub-arcsecond
  accuracy)
• specify all the details of the proposed
  observations schedule will be made by JIVE
  staff
• contact Bob Campbell (campbell_at_jive.nl), to find
  out if preferred correlation mode is OK
• keep in mind the limited resolution (68 mas at
  6cm), uv-coverage and sensitivity
• at the moment
• When 512 Mbps is possible and Effelsberg joins
  the array, the sensitivity will improve
• greatly with Shanghai joining during 2007,
  the resolution will be better as well
• Be ready to travel to JIVE for quick data
  processing
• Think creatively, find projects that make
  appropriate use of this unique service!

30
Future plans
16 Gbps connection to correlator at JIVE
Dynamic scheduling is this possible?
Next generation (software?) correlator
GRID processing