Sub-arcsecond imaging with the International LOFAR Telescope
Astronomy and Astrophysics, vol. 658, pp. A1
Abstract
The International LOFAR Telescope is an interferometer with stations spread across Europe. With baselines of up to ~2000 km, LOFAR has the unique capability of achieving sub-arcsecond resolution at frequencies below 200 MHz. However, it is technically and logistically challenging to process LOFAR data at this resolution. To date only a handful of publications have exploited this capability. Here we present a calibration strategy that builds on previous high-resolution work with LOFAR. It is implemented in a pipeline using mostly dedicated LOFAR software tools and the same processing framework as the LOFAR Two-metre Sky Survey (LoTSS). We give an overview of the calibration strategy and discuss the special challenges inherent to enacting high-resolution imaging with LOFAR, and describe the pipeline, which is publicly available, in detail. We demonstrate the calibration strategy by using the pipeline on P205+55, a typical LoTSS pointing with an 8 h observation and 13 international stations. We perform in-field delay calibration, solution referencing to other calibrators in the field, self-calibration of these calibrators, and imaging of example directions of interest in the field. We find that for this specific field and these ionospheric conditions, dispersive delay solutions can be transferred between calibrators up to ~1.5° away, while phase solution transferral works well over ~1°. We also demonstrate a check of the astrometry and flux density scale with the in-field delay calibrator source. Imaging in 17 directions, we find the restoring beam is typically ~0.3′′ ×0.2′′ although this varies slightly over the entire 5 deg2field of view. We find we can achieve ~80–300 μJy bm−1image rms noise, which is dependent on the distance from the phase centre; typical values are ~90 μJy bm−1for the 8 h observation with 48 MHz of bandwidth. Seventy percent of processed sources are detected, and from this we estimate that we should be able to image roughly 900 sources per LoTSS pointing. This equates to ~ 3 million sources in the northern sky, which LoTSS will entirely cover in the next several years. Future optimisation of the calibration strategy for efficient post-processing of LoTSS at high resolution makes this estimate a lower limit.
Authors 74
-
Affiliation as printed
Centre for Extragalactic Astronomy, Department of Physics, Durham University, Durham DH1 3LE, UK
Institute for Computational Cosmology, Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK
-
Affiliation as printed
Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, School of Natural Sciences, University of Manchester, Manchester M13 9PL, UK
-
Affiliation as printed
School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
-
Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
-
Affiliation as printed
Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, School of Natural Sciences, University of Manchester, Manchester M13 9PL, UK
-
University of Groningen · Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
-
Stockholm University · AlbaNova
Affiliation as printed
Department of Astronomy, AlbaNova University Center, Stockholm University, 10691 Stockholm, Sweden
-
Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
-
Affiliation as printed
Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Emil-Fischer-Str. 31, 97074 Würzburg, Germany
-
Affiliation as printed
Universita di Bologna, Via Zamboni, 33, 40126 Bologna BO, Italy
-
Thüringer Landessternwarte Tautenburg
Affiliation as printed
Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
-
Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
-
Affiliation as printed
School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
-
Royal Observatory · University of Edinburgh
Affiliation as printed
Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
-
Istituto di Radioastronomia di Bologna
Affiliation as printed
INAF – Istituto di Radioastronomia, Via P. Gobetti 101, 40129, Bologna, Italy
-
Leiden University · Leiden Observatory · Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
-
Chalmers University of Technology
Affiliation as printed
Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
-
Swinburne University of Technology
Affiliation as printed
Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail H30, PO Box 218, Hawthorn, VIC 3122, Australia
-
Affiliation as printed
Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
-
University of Groningen · Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
-
Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
-
Instituto de Astrofísica de Andalucía
Affiliation as printed
Instituto de Astrofísica de Andalucía (IAA, CSIC), Glorieta de las Astronomía, s/n, 18008 Granada, Spain
-
Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
-
Centre National de la Recherche Scientifique · Rhodes University · Observatoire de Paris · Galaxies, Etoiles, Physique et Instrumentation · Université Paris Diderot
Affiliation as printed
Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Grahamstown 6140, South Africa
GEPI & USN, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
-
Leiden University · Leiden Observatory · Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
-
Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
-
GFZ Helmholtz Centre for Geosciences · Technische Universität Berlin
Affiliation as printed
GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany
Technische Universität Berlin, Institut für Geodäsie und Geoinformationstechnik, Fakultẗ VI, Sekr. KAI 2-2, Kaiserin-Augusta-Allee 104-106, 10553 Berlin, Germany
-
Shell (India) · Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
Currently at Shell Technology Center, Bangalore 562149, India
-
Science and Technology Corporation (Netherlands) · Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
Science and Technology B.V., Delft, The Netherlands
-
Affiliation as printed
Joint Institute for VLBI ERIC (JIVE), Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
-
Eindhoven University of Technology · Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
Eindhoven University of Technology, De Rondom 70, 5612 AP Eindhoven, The Netherlands
-
Universität Hamburg · Istituto di Radioastronomia di Bologna · University of Bologna
Affiliation as printed
DIFA – Universitá di Bologna, via Gobetti 93/2, 40129 Bologna, Italy
Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
INAF – Istituto di Radioastronomia, Via P. Gobetti 101, 40129, Bologna, Italy
-
Affiliation as printed
Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
-
Affiliation as printed
Research School of Astronomy & Astrophysics, Mt. Stromlo Observatory, Cotter Road, Weston Creek, ACT 2611, Australia
-
Max Planck Institute for Astrophysics
Affiliation as printed
Max-Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, 85748 Garching, Germany
-
Vrije Universiteit Brussel · Radboud University Nijmegen
Affiliation as printed
Astrophysical Institute, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
-
Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
-
Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
-
Universität Hamburg · Istituto di Radioastronomia di Bologna
Affiliation as printed
Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
INAF – Istituto di Radioastronomia, Via P. Gobetti 101, 40129, Bologna, Italy
-
Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
-
Thüringer Landessternwarte Tautenburg
Affiliation as printed
Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
-
Affiliation as printed
Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
-
Affiliation as printed
Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
-
Leiden University · University of Manchester · Leiden Observatory
Affiliation as printed
Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, School of Natural Sciences, University of Manchester, Manchester M13 9PL, UK
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
-
Université d'Orléans · Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · Laboratoire de Physique et Chimie de l’Environnement et de l’Espace · Observatoire Radioastronomique de Nançay
Affiliation as printed
LPC2E – Université d’Orléans/CNRS, 45071 Orléans cedex 2, France
Station de Radioastronomie de Nançay, Observatoire de Paris, PSL Research University, CNRS, Univ. Orléans, OSUC, 18330 Nançay, France
LPC2E – Université d'Orléans/CNRS, 45071 Orléans cedex 2, France
-
Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
-
Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
-
Thüringer Landessternwarte Tautenburg
Affiliation as printed
Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
-
Affiliation as printed
Astronomy, Physics and Statistics Institute of Sciences (APSIS), The George Washington University, Washington, DC 20052, USA
Department of Physics, The George Washington University, 725 21st Street NW, Washington, DC 20052, USA
-
Affiliation as printed
Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute, 44780 Bochum, Germany
-
Affiliation as printed
Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Emil-Fischer-Str. 31, 97074 Würzburg, Germany
-
Affiliation as printed
Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
-
University of Warmia and Mazury in Olsztyn
Affiliation as printed
Space Radio-Diagnostics Research Centre, University of Warmia and Mazury, ul. Romana Prawochenskiego 9, 10-719 Olsztyn, Poland
-
Leibniz Institute for Astrophysics Potsdam
Affiliation as printed
Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
-
Friedrich-Alexander-Universität Erlangen-Nürnberg · Deutsches Elektronen-Synchrotron DESY
Affiliation as printed
DESY, Platanenallee 6, 15738 Zeuthen, Germany
ECAP, Friedrich-Alexander-University Erlangen-Nuremberg, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany
-
Affiliation as printed
SURF/SURFsara, PO Box 94613, 1090 GP Amsterdam, The Netherlands
-
Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
-
Affiliation as printed
CIT, Rijksuniversiteit Groningen, Nettelbosje 1, 9747AJ Groningen, The Netherlands
-
Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
-
Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
-
Lyon 1 Université · Centre National de la Recherche Scientifique · Centre de Recherche Astrophysique de Lyon
Affiliation as printed
Université Claude Bernard Lyon1, Ens de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon, 43 Boulevard du 11 Novembre 1918, 69100 Villeurbanne, France
-
Max Planck Institute for Radio Astronomy
Affiliation as printed
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
-
Affiliation as printed
CBK PAN, Bartycka 18 A, 00-716 Warsaw, Poland
-
Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
-
Affiliation as printed
Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany
-
Leiden University · Leiden Observatory · University of Amsterdam
Affiliation as printed
Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
-
Affiliation as printed
Astronomical Observatory of the Jagiellonian University, ul. Orla171, 30-244 Kraków, Poland
-
Université d'Orléans · Centre National de la Recherche Scientifique · Laboratoire de Physique et Chimie de l’Environnement et de l’Espace
Affiliation as printed
LPC2E – Université d’Orléans/CNRS, 45071 Orléans cedex 2, France
LPC2E – Université d'Orléans/CNRS, 45071 Orléans cedex 2, France
-
Leibniz Institute for Astrophysics Potsdam
Affiliation as printed
Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
-
Affiliation as printed
Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
-
Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
-
Max Planck Institute for Radio Astronomy
Affiliation as printed
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
-
Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · Laboratoire d’études spatiales et d’instrumentation en astrophysique · Observatoire Radioastronomique de Nançay
Affiliation as printed
LESIA, Observatoire de Paris, CNRS, PSL, SU, UP, Place J. Janssen, 92190 Meudon, France
Station de Radioastronomie de Nançay, Observatoire de Paris, PSL Research University, CNRS, Univ. Orléans, OSUC, 18330 Nançay, France
-
Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
Cited by 87 stored of 87
No patents citing this paper on Lens.org (checked 2026-10-11).