LOFAR Facet Calibration
Journal article, 2016
LOFAR, the Low-Frequency Array, is a powerful new radio telescope operating between 10 and 240 MHz. LOFAR allows detailed sensitive high-resolution studies of the low-frequency radio sky. At the same time LOFAR also provides excellent short baseline coverage to map diffuse extended emission. However, producing highquality deep images is challenging due to the presence of direction-dependent calibration errors, caused by imperfect knowledge of the station beam shapes and the ionosphere. Furthermore, the large data volume and presence of station clock errors present additional difficulties. In this paper we present a new calibration scheme, which we name facet calibration, to obtain deep high-resolution LOFAR High Band Antenna images using the Dutch part of the array. This scheme solves and corrects the direction-dependent errors in a number of facets that cover the observed field of view. Facet calibration provides close to thermal noise limited images for a typical 8 hr observing run at similar to 5. resolution, meeting the specifications of the LOFAR Tier-1 northern survey.
algorithm
wide-field
gain calibration
system
techniques: interferometric
self-calibration
w-projection
radio interferometric calibration
astronomy
sky survey
Author
R. J. van Weeren
Harvard-Smithsonian Center for Astrophysics
W. L. Williams
University of Hertfordshire
Netherlands Institute for Radio Astronomy (ASTRON)
Leiden University
M. J. Hardcastle
University of Hertfordshire
T. W. Shimwell
Leiden University
D. Rafferty
University of Hamburg
J. Sabater
University of Edinburgh
G. Heald
Netherlands Institute for Radio Astronomy (ASTRON)
University of Groningen
S. S. Sridhar
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
T. J. Dijkema
Netherlands Institute for Radio Astronomy (ASTRON)
G. Brunetti
Istituto di Radioastronomia
M. Brüggen
University of Hamburg
F. Andrade-Santos
Harvard-Smithsonian Center for Astrophysics
G. Ogrean
Harvard-Smithsonian Center for Astrophysics
H. Rottgering
Leiden University
W. A. Dawson
Lawrence Livermore National Laboratory
W. R. Forman
Harvard-Smithsonian Center for Astrophysics
F. De Gasperin
Leiden University
University of Hamburg
C. G. Jones
Harvard-Smithsonian Center for Astrophysics
G. Miley
Leiden University
L. Rudnick
University of Minnesota
C. L. Sarazin
University of Virginia
A. Bonafede
University of Hamburg
P. N. Best
University of Edinburgh
L. Birzan
University of Hamburg
R. Cassano
Istituto di Radioastronomia
K.T. Chyz̊y
Jagiellonian University in Kraków
J. H. Croston
University of Southampton
T.A. Enßlin
Max Planck Society
C. Ferrari
Observatoire de la Cote d'Azur
M. Hoeft
Thüringer Landessternwarte Tautenburg
Cathy Horellou
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
M. J. Jarvis
University of the Western Cape
University of Oxford
R. P. Kraft
Harvard-Smithsonian Center for Astrophysics
M. Mevius
Netherlands Institute for Radio Astronomy (ASTRON)
H. T. Intema
Leiden University
National Radio Astronomy Observatory
S. S. Murray
Johns Hopkins University
Harvard-Smithsonian Center for Astrophysics
E. Orru
Netherlands Institute for Radio Astronomy (ASTRON)
R. Pizzo
Netherlands Institute for Radio Astronomy (ASTRON)
A. Simionescu
JAXA Institute of Space and Astronautical Science
A. Stroe
Leiden University
S. van der Tol
Netherlands Institute for Radio Astronomy (ASTRON)
G. J. White
Open University
STFC Rutherford Appleton Laboratory
Astrophysical Journal, Supplement Series
0067-0049 (ISSN) 1538-4365 (eISSN)
Vol. 223 1 2Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.3847/0067-0049/223/1/2