Cassiopeia A, Cygnus A, Taurus A, and Virgo A at ultra-low radio frequencies
Journal article, 2020
The four persistent radio sources in the northern sky with the highest flux density at metre wavelengths are Cassiopeia A, Cygnus A, Taurus A, and Virgo A; collectively they are called the A-team. Their flux densities at ultra-low frequencies (< 100 MHz) can reach several thousands of janskys, and they often contaminate observations of the low-frequency sky by interfering with image processing. Furthermore, these sources are foreground objects for all-sky observations hampering the study of faint signals, such as the cosmological 21 cm line from the epoch of reionisation. Aims. We aim to produce robust models for the surface brightness emission as a function of frequency for the A-team sources at ultra-low frequencies. These models are needed for the calibration and imaging of wide-area surveys of the sky with low-frequency interferometers. This requires obtaining images at an angular resolution better than 15″ with a high dynamic range and good image fidelity. Methods. We observed the A-team with the Low Frequency Array (LOFAR) at frequencies between 30 MHz and 77 MHz using the Low Band Antenna system. We reduced the datasets and obtained an image for each A-team source. Results. The paper presents the best models to date for the sources Cassiopeia A, Cygnus A, Taurus A, and Virgo A between 30 MHz and 77 MHz. We were able to obtain the aimed resolution and dynamic range in all cases. Owing to its compactness and complexity, observations with the long baselines of the International LOFAR Telescope will be required to improve the source model for Cygnus A further.
Techniques: interferometric
Radio continuum: general
Author
F. De Gasperin
University of Hamburg
J. Vink
University of Amsterdam
Netherlands Institute for Space Research (SRON)
J. McKean
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
A. Asgekar
Shell Technology Center
Netherlands Institute for Radio Astronomy (ASTRON)
I.M. Avruch
Netherlands Institute for Radio Astronomy (ASTRON)
M. J. Bentum
Netherlands Institute for Radio Astronomy (ASTRON)
Eindhoven University of Technology
R. Blaauw
Netherlands Institute for Radio Astronomy (ASTRON)
A. Bonafede
Istituto di Radioastronomia
University of Bologna
University of Hamburg
J.W. Broderick
Curtin University
M. Brueggen
University of Hamburg
F. Breitling
Leibniz Association
W. N. Brouw
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
H. R. Butcher
Australian National University
B. Ciardi
Max Planck Society
V. Cuciti
University of Hamburg
M. De Vos
Netherlands Institute for Radio Astronomy (ASTRON)
S. Duscha
Netherlands Institute for Radio Astronomy (ASTRON)
J. Eisloffel
Thüringer Landessternwarte Tautenburg
D. Engels
University of Hamburg
R. A. Fallows
Netherlands Institute for Radio Astronomy (ASTRON)
T. M.O. Franzen
Netherlands Institute for Radio Astronomy (ASTRON)
M. A. Garrett
Leiden University
University of Manchester
A.W. Gunst
Netherlands Institute for Radio Astronomy (ASTRON)
J.R. Hörandel
National Institute for Subatomic Physics (NIKHEF)
Vrije Universiteit Brussel (VUB)
Radboud University
G. Heald
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
M. Hoeft
Thüringer Landessternwarte Tautenburg
M. Iacobelli
Netherlands Institute for Radio Astronomy (ASTRON)
L.V.E. Koopmans
University of Groningen
A. Krankowski
University of Warmia and Mazury in Olsztyn
P. Maat
Netherlands Institute for Radio Astronomy (ASTRON)
G. Mann
Leibniz Association
M. Mevius
Netherlands Institute for Radio Astronomy (ASTRON)
G. Miley
Leiden University
R. Morganti
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
A. Nelles
Deutsches Elektronen-Synchrotron (DESY)
University of Erlangen-Nuremberg (FAU)
M. J. Norden
Netherlands Institute for Radio Astronomy (ASTRON)
A. R. Offringa
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
E. Orrú
Netherlands Institute for Radio Astronomy (ASTRON)
H. Paas
University of Groningen
V. N. Pandey
Netherlands Institute for Radio Astronomy (ASTRON)
University of Groningen
M. Pandey-Pommier
CRAL Le Centre de Recherche Astronomique de Lyon
Station de Radioastronomie de Nançay
R. Pekal
Poznanskie Centrum Superkomputerowo Sieciowe
R. Pizzo
Netherlands Institute for Radio Astronomy (ASTRON)
W. Reich
Max Planck Society
A. Rowlinson
University of Amsterdam
Netherlands Institute for Radio Astronomy (ASTRON)
H. Rottgering
Leiden University
D. J. Schwarz
Bielefeld University
A. Shulevski
University of Amsterdam
O. Smirnov
Observatory
Rhodes University
C. Sobey
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
M. Soida
Jagiellonian University in Kraków
M. Steinmetz
Leibniz Association
M. Tagger
University of Orléans
M. C. Toribio
Arnold van Ardenne
Netherlands Institute for Radio Astronomy (ASTRON)
A. J. van der Horst
George Washington University
M. P. van Haarlem
Netherlands Institute for Radio Astronomy (ASTRON)
R. van Weeren
Leiden University
C. Vocks
Leibniz Association
O. Wucknitz
Max Planck Society
P.M. Zarka
Université Paris PSL
P. Zucca
Netherlands Institute for Radio Astronomy (ASTRON)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 635 A150Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Geophysics
Signal Processing
DOI
10.1051/0004-6361/201936844