LBCS: The LOFAR Long-Baseline Calibrator Survey
Journal article, 2016
We outline the LOFAR Long-Baseline Calibrator Survey (LBCS), whose aim is to identify sources suitable for calibrating the highest-resolution observations made with the International LOFAR Telescope, which include baselines > 1000 km. Suitable sources must contain significant correlated flux density (greater than or similar to 50 - 100 mJy) at frequencies around 110-190 MHz on scales of a few hundred milliarcseconds. At least for the 200-300-km international baselines, we find around 1 suitable calibrator source per square degree over a large part of the northern sky, in agreement with previous work. This should allow a randomly selected target to be successfully phase calibrated on the international baselines in over 50% of cases. Products of the survey include calibrator source lists and fringe-rate and delay maps of wide areas-typically a few degrees-around each source. The density of sources with significant correlated flux declines noticeably with baseline length over the range 200-600 km, with good calibrators on the longest baselines appearing only at the rate of 0.5 per sq. deg. Coherence times decrease from 1-3 min on 200-km baselines to about 1 min on 600-km baselines, suggesting that ionospheric phase variations contain components with scales of a few hundred kilometres. The longest median coherence time, at just over 3 min, is seen on the DE609 baseline, which at 227 km is close to being the shortest. We see median coherence times of between 80 and 110 s on the four longest baselines (580-600 km), and about 2 min for the other baselines. The success of phase transfer from calibrator to target is shown to be influenced by distance, in a manner that suggests a coherence patch at 150-MHz of the order of 1 deg. Although source structures cannot be measured in these observations, we deduce that phase transfer is affected if the calibrator source structure is not known. We give suggestions for calibration strategies and choice of calibrator sources, and describe the access to the online catalogue and data products.
galaxies: active
surveys
instrumentation: interferometers
radio continuum: galaxies
techniques: interferometric
Author
N. Jackson
University of Manchester
A. Tagore
University of Manchester
A. Deller
Netherlands Institute for Radio Astronomy (ASTRON)
J. Moldon
Netherlands Institute for Radio Astronomy (ASTRON)
University of Manchester
Eskil Varenius
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
L. Morabito
Leiden University
O. Wucknitz
Max Planck Society
Tobia Carozzi
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
John Conway
Chalmers, Earth and Space Sciences, Onsala Space Observatory
A. Drabent
Thüringer Landessternwarte Tautenburg
A. D. Kapinska
ARC Centre of Excellence for All-sky Astrophysics (CAASTRO)
University of Portsmouth
University of Western Australia
E. Orru
Netherlands Institute for Radio Astronomy (ASTRON)
M. Brentjens
Netherlands Institute for Radio Astronomy (ASTRON)
R. Blaauw
Netherlands Institute for Radio Astronomy (ASTRON)
G. Kuper
Netherlands Institute for Radio Astronomy (ASTRON)
J. Sluman
Netherlands Institute for Radio Astronomy (ASTRON)
J. Schaap
Netherlands Institute for Radio Astronomy (ASTRON)
N. Vermaas
Netherlands Institute for Radio Astronomy (ASTRON)
M. Iacobelli
Netherlands Institute for Radio Astronomy (ASTRON)
L. Cerrigone
Netherlands Institute for Radio Astronomy (ASTRON)
A. Shulevski
Netherlands Institute for Radio Astronomy (ASTRON)
S. ter Veen
Netherlands Institute for Radio Astronomy (ASTRON)
R. A. Fallows
Netherlands Institute for Radio Astronomy (ASTRON)
R. Pizzo
Netherlands Institute for Radio Astronomy (ASTRON)
M. Sipior
Netherlands Institute for Radio Astronomy (ASTRON)
J. Anderson
German Research Centre for Geosciences (GFZ)
I. M. Avruch
University of Groningen
Netherlands Institute for Space Research (SRON)
M. E. Bell
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
I. van Bemmel
Joint Institute for VLBI in Europe (JIVE)
M. J. Bentum
University of Twente
Netherlands Institute for Radio Astronomy (ASTRON)
P. Best
University of Edinburgh
A. Bonafede
University of Hamburg
F. Breitling
Leibniz Institute for Astrophysics Potsdam
J. W. Broderick
Netherlands Institute for Radio Astronomy (ASTRON)
W. N. Brouw
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
M. Brüggen
University of Hamburg
B. Ciardi
Max Planck Society
A. Corstanje
Radboud University
F. De Gasperin
Leiden University
E. de Geus
Netherlands Institute for Radio Astronomy (ASTRON)
SmarterVision BV
J. Eisloffel
Max Planck Society
D. Engels
University of Hamburg
H. Falcke
Radboud University
Netherlands Institute for Radio Astronomy (ASTRON)
M. A. Garrett
Netherlands Institute for Radio Astronomy (ASTRON)
Leiden University
J. M. Griessmeier
University of Orléans
A. W. Gunst
Netherlands Institute for Radio Astronomy (ASTRON)
M. P. van Haarlem
Netherlands Institute for Radio Astronomy (ASTRON)
G. Heald
Netherlands Institute for Radio Astronomy (ASTRON)
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
University of Groningen
M. Hoeft
Thüringer Landessternwarte Tautenburg
J. Horandel
Radboud University
A. Horneffer
Max Planck Society
H. Intema
Leiden University
National Radio Astronomy Observatory Socorro
E. Juette
Ruhr-Universität Bochum
M. Kuniyoshi
National Astronomical Observatory of Japan
J. van Leeuwen
University of Amsterdam
Netherlands Institute for Radio Astronomy (ASTRON)
G. M. Loose
Netherlands Institute for Radio Astronomy (ASTRON)
P. Maat
Netherlands Institute for Radio Astronomy (ASTRON)
R. McFadden
Netherlands Institute for Radio Astronomy (ASTRON)
D. McKay-Bukowski
STFC Rutherford Appleton Laboratory
Sodankyla Geophysical Observatory
J. P. McKean
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
D. D. Mulcahy
University of Manchester
H. Munk
Radboud University
Netherlands Institute for Radio Astronomy (ASTRON)
M. Pandey-Pommier
Lyon Observatory
A. G. Polatidis
Netherlands Institute for Radio Astronomy (ASTRON)
W. Reich
Max Planck Society
H. Rottgering
Leiden University
A. Rowlinson
Netherlands Institute for Radio Astronomy (ASTRON)
University of Amsterdam
A. M. M. Scaife
University of Manchester
D. J. Schwarz
Bielefeld University
M. Steinmetz
Leibniz Institute for Astrophysics Potsdam
J. Swinbank
Princeton University
S. Thoudam
Radboud University
M. C. Toribio
Netherlands Institute for Radio Astronomy (ASTRON)
Leiden University
R. Vermeulen
Netherlands Institute for Radio Astronomy (ASTRON)
C. Vocks
Leibniz Institute for Astrophysics Potsdam
R. J. van Weeren
Harvard-Smithsonian Center for Astrophysics
M. W. Wise
Netherlands Institute for Radio Astronomy (ASTRON)
University of Amsterdam
S. Yatawatta
Netherlands Institute for Radio Astronomy (ASTRON)
P. Zarka
LESIA - Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 595 Art no A86- A86Advanced Radio Astronomy in Europe (RADIONET3)
(EC/FP7/283393), 2012-01-01 -- 2015-12-31.
Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201629016