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.
w-projection
system
sky survey
self-calibration
wide-field
astronomy
algorithm
techniques: interferometric
gain calibration
radio interferometric calibration
Author
R. J. van Weeren
Harvard-Smithsonian Center for Astrophysics
W. L. Williams
Leiden Observatory Research Institute
Netherlands Foundation for Research in Astronomy
University of Hertfordshire
M. J. Hardcastle
University of Hertfordshire
T. W. Shimwell
Leiden Observatory Research Institute
D. Rafferty
Universitat Hamburg
J. Sabater
University of Edinburgh
G. Heald
University of Groningen, Kapteyn Astronomical Institute
Netherlands Foundation for Research in Astronomy
S. S. Sridhar
University of Groningen, Kapteyn Astronomical Institute
Netherlands Foundation for Research in Astronomy
T. J. Dijkema
Netherlands Foundation for Research in Astronomy
G. Brunetti
Istituto Di Radioastronomia, Bologna
M. Brüggen
Universitat Hamburg
F. Andrade-Santos
Harvard-Smithsonian Center for Astrophysics
G. Ogrean
Harvard-Smithsonian Center for Astrophysics
H. Rottgering
Leiden Observatory Research Institute
W. A. Dawson
Lawrence Livermore National Laboratory
W. R. Forman
Harvard-Smithsonian Center for Astrophysics
F. De Gasperin
Universitat Hamburg
Leiden Observatory Research Institute
C. G. Jones
Harvard-Smithsonian Center for Astrophysics
G. Miley
Leiden Observatory Research Institute
L. Rudnick
University of Minnesota System
C. L. Sarazin
University of Virginia
A. Bonafede
Universitat Hamburg
P. N. Best
University of Edinburgh
L. Birzan
Universitat Hamburg
R. Cassano
Istituto Di Radioastronomia, Bologna
K.T. Chyz̊y
Uniwersytet Jagiellonski w Krakowie
J. H. Croston
University of Southampton
T.A. Enßlin
Max Planck Institut fur Astrophysik
C. Ferrari
Observatoire de la Cote d'Azur
M. Hoeft
Thuringer 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 Foundation for Research in Astronomy
H. T. Intema
Leiden Observatory Research Institute
National Radio Astronomy Observatory
S. S. Murray
Johns Hopkins University
Harvard-Smithsonian Center for Astrophysics
E. Orru
Netherlands Foundation for Research in Astronomy
R. Pizzo
Netherlands Foundation for Research in Astronomy
A. Simionescu
JAXA Institute of Space and Astronautical Science
A. Stroe
Leiden Observatory Research Institute
S. van der Tol
Netherlands Foundation for Research in Astronomy
G. J. White
Rutherford Appleton Laboratory
Open University
Astrophysical Journal, Supplement Series
0067-0049 (ISSN) 1538-4365 (eISSN)
Vol. 223 1 2Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.3847/0067-0049/223/1/2