The LOFAR Multifrequency Snapshot Sky Survey (MSSS)

I. Survey description and first results

¹ ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
e-mail: heald@astron.nl
² Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
³ School of Physics and Astronomy, University of Southampton, SO17 1BJ, UK
⁴ Anton Pannekoek Institute, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
⁵ Laboratoire Lagrange, UMR 7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur, 06300 Nice, France
⁶ School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
⁷ Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland
⁸ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁹ Universität Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁰ Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
¹¹ Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
¹² Department of Astronomy, University of Washington, PO Box 351580, Seattle, WA 98195, USA
¹³ LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France
¹⁴ Department of Physics & Astronomy, The Open University, Milton Keynes MK7 6AA, UK
¹⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁶ IMAPP/Department of Astrophysics, Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands
¹⁷ CRAL, Observatoire de Lyon, Université Lyon 1, 9 avenue Ch. André, 69561 Saint Genis Laval Cedex, France
¹⁸ School of Chemical & Physical Sciences, Victoria University of Wellington, PO Box 600, 6140 Wellington, New Zealand
¹⁹ CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia
²⁰ Institute for Astronomy (IfA), University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
²¹ Centrum Wiskunde & Informatica, PO Box 94079, 1090 GB Amsterdam, The Netherlands
²² Astronomisches Institut der Universität Bochum, Universitätsstr. 150, 44801 Bochum, Germany
²³ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
²⁴ SKA South Africa, 3rd Floor, The Park, Park Road, 7405 Pinelands, South Africa
²⁵ Department of Physics & Electronics, Rhodes University, PO Box 94, 6140 Grahamstown, South Africa
²⁶ Dr. Remeis Sternwarte & ECAP, Universität Erlangen-Nürnberg, Sternwartstrasse 7, 96049 Bamberg, Germany
²⁷ Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Emil-Fischer-Str. 31, 97074 Würzburg, Germany
²⁸ Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
²⁹ Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA
³⁰ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³¹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³² Helmholtz-Zentrum Potsdam, DeutschesGeoForschungsZentrum GFZ, Department 1: Geodesy and Remote Sensing, Telegrafenberg, A17, 14473 Potsdam, Germany
³³ SRON Netherlands Insitute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
³⁴ Joint Institute for VLBI in Europe, Dwingeloo, Postbus 2, 7990 AA The Netherlands
³⁵ University of Twente, 7522 NB Enschede, The Netherlands
³⁶ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
³⁷ Research School of Astronomy and Astrophysics, Australian National University, Mt Stromlo Obs., via Cotter Road, Weston, A.C.T. 2611, Australia
³⁸ SmarterVision BV, Oostersingel 5, 9401 JX Assen, The Netherlands
³⁹ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
⁴⁰ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
⁴¹ LPC2E – Université d’Orléans/CNRS, 45071 Orléans Cedex 2, France
⁴² Station de Radioastronomie de Nançay, Observatoire de Paris – CNRS/INSU, USR 704 – Univ. Orléans, OSUC, route de Souesmes, 18330 Nançay, France
⁴³ National Radio Astronomy Observatory, 520Edgemont Road, Charlottesville, VA 22903-2475, USA
⁴⁴ Jodrell Bank Center for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK
⁴⁵ Astro Space Center of the Lebedev Physical Institute, Profsoyuznaya str. 84/32, 117997 Moscow, Russia
⁴⁶ National Astronomical Observatory of Japan, 2 Chome-21-1 Osawa, Mitaka, Tokyo, Japan
⁴⁷ Department of Astronomy, University of California, Berkeley, USA
⁴⁸ Sodankylä Geophysical Observatory, University of Oulu, Tähteläntie 62, 99600 Sodankylä, Finland
⁴⁹ STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot OX11 0QX, UK
⁵⁰ International Centre for Radio Astronomy Research – Curtin University, GPO Box U1987, Perth, WA 6845, Australia
⁵¹ Center for Information Technology (CIT), University of Groningen, 9712 CP Groningen, The Netherlands
⁵² Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany

Received: 24 October 2014
Accepted: 20 July 2015

Abstract

We present the Multifrequency Snapshot Sky Survey (MSSS), the first northern-sky Low Frequency Array (LOFAR) imaging survey. In this introductory paper, we first describe in detail the motivation and design of the survey. Compared to previous radio surveys, MSSS is exceptional due to its intrinsic multifrequency nature providing information about the spectral properties of the detected sources over more than two octaves (from 30 to 160 MHz). The broadband frequency coverage, together with the fast survey speed generated by LOFAR’s multibeaming capabilities, make MSSS the first survey of the sort anticipated to be carried out with the forthcoming Square Kilometre Array (SKA). Two of the sixteen frequency bands included in the survey were chosen to exactly overlap the frequency coverage of large-area Very Large Array (VLA) and Giant Metrewave Radio Telescope (GMRT) surveys at 74 MHz and 151 MHz respectively. The survey performance is illustrated within the MSSS Verification Field (MVF), a region of 100 square degrees centered at (α,δ)_J2000 = (15^h,69°). The MSSS results from the MVF are compared with previous radio survey catalogs. We assess the flux and astrometric uncertainties in the catalog, as well as the completeness and reliability considering our source finding strategy. We determine the 90% completeness levels within the MVF to be 100 mJy at 135 MHz with 108″ resolution, and 550 mJy at 50 MHz with 166″ resolution. Images and catalogs for the full survey, expected to contain 150 000–200 000 sources, will be released to a public web server. We outline the plans for the ongoing production of the final survey products, and the ultimate public release of images and source catalogs.