LBCS: The LOFAR long baseline snapshot calibrator survey
Journal article, 2015
Aims. An efficient means of locating calibrator sources for international LOw Frequency ARray (LOFAR) is developed and used to determine the average density of usable calibrator sources on the sky for subarcsecond observations at 140 MHz.
Methods. We used the multi-beaming capability of LOFAR to conduct a fast and computationally inexpensive survey with the full international LOFAR array. Sources were preselected on the basis of 325 MHz arcminute-scale flux density using existing catalogues. By observing 30 different sources in each of the 12 sets of pointings per hour, we were able to inspect 630 sources in two hours to determine if they possess a sufficiently bright compact component to be usable as LOFAR delay calibrators.
Results. More than 40% of the observed sources are detected on multiple baselines between international stations and 86 are classified as satisfactory calibrators. We show that a flat low-frequency spectrum (from 74 to 325 MHz) is the best predictor of compactness at 140 MHz. We extrapolate from our sample to show that the sky density of calibrators that are sufficiently bright to calibrate dispersive and non-dispersive delays for the international LOFAR using existing methods is 1.0 per square degree.
Conclusions. The observed density of satisfactory delay calibrator sources means that observations with international LOFAR should be possible at virtually any point in the sky provided that a fast and efficient search, using the methodology described here, is conducted prior to the observation to identify the best calibrator.
instrumentation: interferometers
catalogs
techniques: high angular resolution
methods: observational
instrumentation: high angular resolution
techniques: interferometric
Author
J. Moldon
Netherlands Institute for Radio Astronomy (ASTRON)
A. T. Deller
Netherlands Institute for Radio Astronomy (ASTRON)
O. Wucknitz
Max-Planck Institute for Radio Astronomy
N. Jackson
University of Manchester
A. Drabent
Thüringer Landessternwarte Tautenburg
Tobia Carozzi
Chalmers, Earth and Space Sciences, Onsala Space Observatory
John Conway
Chalmers, Earth and Space Sciences, Onsala Space Observatory
A. D. Kapinska
ARC Centre of Excellence for All-sky Astrophysics (CAASTRO)
Curtin University
University of Portsmouth
J. P. McKean
Netherlands Institute for Radio Astronomy (ASTRON)
L. Morabito
Leiden University
Eskil Varenius
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
P. Zarka
Centre national de la recherche scientifique (CNRS)
J. Anderson
German Research Centre for Geosciences (GFZ)
A. Asgekar
Netherlands Institute for Radio Astronomy (ASTRON)
Shell Technology Center
I. M. Avruch
Netherlands Institute for Space Research (SRON)
Kapteyn Astronomical Institute
M. E. Bell
CSIRO Astronomy and Space Science
M. J. Bentum
University of Twente
Netherlands Institute for Radio Astronomy (ASTRON)
G. Bernardi
Harvard-Smithsonian Center for Astrophysics
P. Best
University of Edinburgh
L. Birzan
Leiden University
J. Bregman
Netherlands Institute for Radio Astronomy (ASTRON)
F. Breitling
Leibniz Institute for Astrophysics Potsdam
J. W. Broderick
University of Oxford
University of Southampton
M. Brüggen
University of Hamburg
H. R. Butcher
Australian National University
D. Carbone
University of Amsterdam
B. Ciardi
MPIA
F. De Gasperin
University of Hamburg
E. de Geus
SmarterVision BV
Netherlands Institute for Radio Astronomy (ASTRON)
S. Duscha
Netherlands Institute for Radio Astronomy (ASTRON)
J. Eisloffel
Thüringer Landessternwarte Tautenburg
D. Engels
University of Hamburg
H. Falcke
Netherlands Institute for Radio Astronomy (ASTRON)
Radboud University
R. A. Fallows
Netherlands Institute for Radio Astronomy (ASTRON)
R. Fender
University of Oxford
C. Ferrari
Centre national de la recherche scientifique (CNRS)
W. Frieswijk
Netherlands Institute for Radio Astronomy (ASTRON)
M. A. Garrett
Leiden University
Netherlands Institute for Radio Astronomy (ASTRON)
J. Griessmeier
University of Orléans
A. W. Gunst
Netherlands Institute for Radio Astronomy (ASTRON)
J. P. Hamaker
Netherlands Institute for Radio Astronomy (ASTRON)
T. E. Hassall
University of Southampton
G. Heald
Netherlands Institute for Radio Astronomy (ASTRON)
M. Hoeft
Thüringer Landessternwarte Tautenburg
B. Juette
Ruhr-Universität Bochum
A. Karastergiou
University of Oxford
V. I. Kondratiev
Astro Space Center of Lebedev Physical Institute
Netherlands Institute for Radio Astronomy (ASTRON)
M. Kramer
University of Manchester
Max-Planck Institute for Radio Astronomy
M. Kuniyoshi
Max-Planck Institute for Radio Astronomy
G. Kuper
Netherlands Institute for Radio Astronomy (ASTRON)
P. Maat
Netherlands Institute for Radio Astronomy (ASTRON)
G. Mann
Leibniz Institute for Astrophysics Potsdam
S. Markoff
University of Amsterdam
R. McFadden
Netherlands Institute for Radio Astronomy (ASTRON)
D. McKay-Bukowski
University of Oulu
STFC Rutherford Appleton Laboratory
R. Morganti
Netherlands Institute for Radio Astronomy (ASTRON)
Kapteyn Astronomical Institute
H. Munk
Netherlands Institute for Radio Astronomy (ASTRON)
M. J. Norden
Netherlands Institute for Radio Astronomy (ASTRON)
A. R. Offringa
Australian National University
E. Orru
Netherlands Institute for Radio Astronomy (ASTRON)
H. Paas
University of Groningen
M. Pandey-Pommier
Lyon Observatory
R. Pizzo
Netherlands Institute for Radio Astronomy (ASTRON)
A. G. Polatidis
Netherlands Institute for Radio Astronomy (ASTRON)
W. Reich
Max-Planck Institute for Radio Astronomy
H. Rottgering
Leiden University
A. Rowlinson
CSIRO Astronomy and Space Science
A. M. M. Scaife
University of Southampton
D. Schwarz
Bielefeld University
J. Sluman
Netherlands Institute for Radio Astronomy (ASTRON)
O. Smirnov
Square Kilometre Array, South Africa
Rhodes University
B. W. Stappers
University of Manchester
M. Steinmetz
Leibniz Institute for Astrophysics Potsdam
M. Tagger
University of Orléans
Y. Tang
Netherlands Institute for Radio Astronomy (ASTRON)
C. Tasse
Bielefeld University
S. Thoudam
Radboud University
M. C. Toribio
Netherlands Institute for Radio Astronomy (ASTRON)
R. Vermeulen
Netherlands Institute for Radio Astronomy (ASTRON)
C. Vocks
Leibniz Institute for Astrophysics Potsdam
R. J. van Weeren
Harvard-Smithsonian Center for Astrophysics
S. White
Max-Planck Institute for Radio Astronomy
M. W. Wise
Netherlands Institute for Radio Astronomy (ASTRON)
University of Amsterdam
S. Yatawatta
Netherlands Institute for Radio Astronomy (ASTRON)
A. Zensus
Max-Planck Institute for Radio Astronomy
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 574 Art. no. A73- 25042Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201425042