LOFAR calibration and wide-field imaging

Cyril Tasse; Ger van Diepen; Sebastiaan van der Tol; Reinout J. van Weeren; Joris E. van Zwieten; Fabien Batejat; Sanjay Bhatnagar; Ilse van Bemmel; Laura Bîrzan; Annalisa Bonafede; John Conway; Chiara Ferrari; Francesco De Gasperin; Kumar Golap; George Heald; Neal Jackson; Giulia Macario; John McKean; Niruj Mohan; Emanuela Orrù; Roberto Pizzo; David Rafferty; Urvashi Rau; Huub Röttgering; Aleksandar Shulevski; on behalf of the LOFAR Collaboration

doi:10.1016/j.crhy.2011.10.006

The next generation radiotelescopes / Les radiotélescopes du futur

LOFAR calibration and wide-field imaging
[Étalonnage de LOFAR et lʼimagerie en champ large]

Cyril Tasse ¹ ; Ger van Diepen ² ; Sebastiaan van der Tol ³ ; Reinout J. van Weeren ³ ; Joris E. van Zwieten ³ ; Fabien Batejat ⁴ ; Sanjay Bhatnagar ⁵ ; Ilse van Bemmel ² ; Laura Bîrzan ³ ; Annalisa Bonafede ⁶ ; John Conway ⁴ ; Chiara Ferrari ⁷ ; Francesco De Gasperin ⁸ ; Kumar Golap ⁵ ; George Heald ² ; Neal Jackson ⁹ ; Giulia Macario ⁷ ; John McKean ² ; Niruj Mohan ³ ; Emanuela Orrù ¹⁰ ; Roberto Pizzo ² ; David Rafferty ³ ; Urvashi Rau ⁵ ; Huub Röttgering ³ ; Aleksandar Shulevski ¹⁰ ; on behalf of the LOFAR Collaboration

¹ GEPI, observatoire de Paris-Meudon, 5 place Jules-Janssen, 92190 Meudon, France
² ASTRON, Postbus 2, 7990 AA Dwingeloo, The Netherlands
³ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁴ Onsala Space Observatory, Chalmers University of Technology, 43992 Onsala, Sweden
⁵ National Radio Astronomy Observatory, Socorro, NM 87801, USA
⁶ INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
⁷ UNS, CNRS UMR 6202 Cassiopée, observatoire de la Côte dʼAzur, 06300 Nice, France
⁸ Max-Planck-Institut für Astrophysik, Karl-Schwarzschildstraße 1, 85741 Garching, Germany
⁹ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
¹⁰ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands

Comptes Rendus. Physique, Volume 13 (2012) no. 1, pp. 28-32.

Résumé
Abstract

LOFAR est un instrument au design révolutionnaire qui opère à très basses fréquences ( $\sim 10 – 240 MHz$ ) dans un domaine dʼénergie quasiment inexploré. Il est construit presque entièrement en software, et allie réseau phasé et interféromètre. Son utilisation conduira à des avancées scientifiques majeures, mais elle représente un défi technologique considérable. En effet, la sensibilité et le champ de vue de cet instrument étant accru de plusieurs ordres de grandeur par rapport à lʼancienne génération, des phénomènes subtils doivent être considérés. Dʼautre part, les nouvelles technologies utilisées comme les réseaux phasés entraînent des complications de taille. Dans le cadre du groupe de travail « relevés LOFAR » nous développons des procédures dʼétalonnage (ionosphère, lobes de station). Dans le cadre de ces problématiques, de nouvelles difficultés émergent, et les concepts de complexité algorithmique et de parallélisabilité deviennent une base de réflexion.

LOFAR is a revolutionary instrument, operating at low frequencies ( $ν ≲ 240 MHz$ ). It will drive major breakthroughs in the area of observational cosmology, but its use requires the development of challenging techniques and algorithms. Since its field of view and sensitivity are increased by orders of magnitude as compared to the older generation of instruments, new technical problems have to be addressed. The LOFAR survey team is in charge of commissioning the first LOFAR data produced in the imager mode as part of building the imaging pipeline. We are developing algorithms to tackle the problems associated with calibration (ionosphere, beam, etc.) and wide-field imaging for the achievement of the deep extragalactic surveys. New types of problems arise in that context, and notions such as algorithmic complexity and parallelism become fundamental.

Publié le : 2011-12-14

DOI : 10.1016/j.crhy.2011.10.006

Keywords: LOFAR, Interferometry, Calibration, Imaging
Mot clés : LOFAR, Interférométrie, Calibration, Imagerie

Affiliations des auteurs :

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     title = {LOFAR calibration and wide-field imaging},
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%A Kumar Golap
%A George Heald
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%A Niruj Mohan
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%A Roberto Pizzo
%A David Rafferty
%A Urvashi Rau
%A Huub Röttgering
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Cyril Tasse; Ger van Diepen; Sebastiaan van der Tol; Reinout J. van Weeren; Joris E. van Zwieten; Fabien Batejat; Sanjay Bhatnagar; Ilse van Bemmel; Laura Bîrzan; Annalisa Bonafede; John Conway; Chiara Ferrari; Francesco De Gasperin; Kumar Golap; George Heald; Neal Jackson; Giulia Macario; John McKean; Niruj Mohan; Emanuela Orrù; Roberto Pizzo; David Rafferty; Urvashi Rau; Huub Röttgering; Aleksandar Shulevski; on behalf of the LOFAR Collaboration. LOFAR calibration and wide-field imaging. Comptes Rendus. Physique, Volume 13 (2012) no. 1, pp. 28-32. doi : 10.1016/j.crhy.2011.10.006. https://comptes-rendus.academie-sciences.fr/physique/articles/10.1016/j.crhy.2011.10.006/

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