Cassiopeia A, Cygnus A, Taurus A, and Virgo A at ultra-low radio frequencies
Artikel i vetenskaplig tidskrift, 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
Författare
F. De Gasperin
Universität Hamburg
J. Vink
Universiteit Van Amsterdam
Netherlands Institute for Space Research (SRON)
J. McKean
Rijksuniversiteit 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)
Technische Universiteit Eindhoven
R. Blaauw
Netherlands Institute for Radio Astronomy (ASTRON)
A. Bonafede
Istituto di Radioastronomia
Universita di Bologna
Universität Hamburg
J.W. Broderick
Curtin University
M. Brueggen
Universität Hamburg
F. Breitling
Leibniz-Gemeinschaft
W. N. Brouw
Rijksuniversiteit Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
H. R. Butcher
Australian National University
B. Ciardi
Max-Planck-Gesellschaft
V. Cuciti
Universität 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
Universität Hamburg
R. A. Fallows
Netherlands Institute for Radio Astronomy (ASTRON)
T. M.O. Franzen
Netherlands Institute for Radio Astronomy (ASTRON)
M. A. Garrett
Universiteit Leiden
University of Manchester
A.W. Gunst
Netherlands Institute for Radio Astronomy (ASTRON)
J.R. Hörandel
National Institute for Subatomic Physics (NIKHEF)
Vrije Universiteit Brüssel (VUB)
Radboud Universiteit
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
Rijksuniversiteit Groningen
A. Krankowski
University of Warmia and Mazury in Olsztyn
P. Maat
Netherlands Institute for Radio Astronomy (ASTRON)
G. Mann
Leibniz-Gemeinschaft
M. Mevius
Netherlands Institute for Radio Astronomy (ASTRON)
G. Miley
Universiteit Leiden
R. Morganti
Rijksuniversiteit Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
A. Nelles
Deutsches Elektronen-Synchrotron (DESY)
Friedrich-Alexander-Universität Erlangen Nurnberg (FAU)
M. J. Norden
Netherlands Institute for Radio Astronomy (ASTRON)
A. R. Offringa
Rijksuniversiteit Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
E. Orrú
Netherlands Institute for Radio Astronomy (ASTRON)
H. Paas
Rijksuniversiteit Groningen
V. N. Pandey
Netherlands Institute for Radio Astronomy (ASTRON)
Rijksuniversiteit 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-Gesellschaft
A. Rowlinson
Universiteit Van Amsterdam
Netherlands Institute for Radio Astronomy (ASTRON)
H. Rottgering
Universiteit Leiden
D. J. Schwarz
Universität Bielefeld
A. Shulevski
Universiteit Van Amsterdam
O. Smirnov
Observatory
Rhodes University
C. Sobey
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
M. Soida
Uniwersytet Jagiellonski w Krakowie
M. Steinmetz
Leibniz-Gemeinschaft
M. Tagger
Universite d'Orleans
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
Universiteit Leiden
C. Vocks
Leibniz-Gemeinschaft
O. Wucknitz
Max-Planck-Gesellschaft
P.M. Zarka
Université de recherche Paris Sciences et Lettres
P. Zucca
Netherlands Institute for Radio Astronomy (ASTRON)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 635 A150Ämneskategorier (SSIF 2011)
Astronomi, astrofysik och kosmologi
Geofysik
Signalbehandling
DOI
10.1051/0004-6361/201936844