Volume 615, July 2018
|Number of page(s)||8|
|Published online||19 July 2018|
Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR
ASTRON, Netherlands Institute for Radio Astronomy,
2 Astrophysics Research Group, School of Physics, Trinity College Dublin, Dublin 2, Ireland
3 Institut de Recherche en Astrophysique et Planétologie, 9 Av. du Colonel Roche, 31028 Toulouse Cedex 4, France
4 Solar-Terrestrial Center of Excellence, Royal Observatory of Belgium, Av. Circulaire 3, 1180 Brussels, Belgium
5 LESIA, UMR CNRS 8109, Observatoire de Paris, 92195 Meudon, France
6 Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
7 RAL Space, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Oxfordshire, UK
8 SUPA School of Physics and Astronomy, University of Glasgow, G12 8QQ, UK
9 Space Research Centre of the Polish Academy of Science, 18A Bartycka 00-716 Warsaw, Poland
10 Space Radio-Diagnostics Research Centre, University of Warmia and Mazury in Olsztyn, Poland
11 Helmholtz-Zentrum Potsdam, DeutschesGeoForschungsZentrum GFZ, Geodesy and Remote Sensing, Telegrafenberg, A17, 14473 Potsdam, Germany
12 Shell Technology Center, Bangalore, India
13 University of Technology Sydney, 15 Broadway, Ultimo NSW 2007, Australia
14 Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
15 Institute for Astronomy, University of Edinburgh, Royal Observatory of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
16 Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
17 University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
18 Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 Australia
19 Max Planck Institute for Astrophysics, Karl Schwarzschild Str. 1, 85741 Garching, Germany
20 SmarterVision BV, Oostersingel 5, 9401 JX Assen, The Netherlands
21 Centre for Astrophysics & Supercomputing, Swinburne University of Technology John St, Hawthorn VIC 3122, Australia
22 Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
23 Jodrell Bank Center for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK
24 Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands
25 LPC2E - Univ. d’Orléans/CNRS, 3A Av. de la Recherche Scientifique, 45071 Orléans Cedex 2, France
26 Station de Radioastronomie de Nancay, Observatoire de Paris CNRS/INSU, USR 704 - Univ., OSUC route de Souesmes, 18330 Nancay, France
27 CSIRO Astronomy and Space Science, 26 Dick Perry Av., Kensington, WA 6151, Australia
28 Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
29 Astronomisches Institut der Ruhr-Universität Bochum, Universitaetsstrasse 150, 44780 Bochum, Germany
30 Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
31 Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
32 Department of Physics and Technology, University of Troms, Norway
33 STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot OX11 0QX, UK
34 Radboud University Radio Lab, Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
35 Department of Physics and Astronomy, University of California Irvine, Irvine, CA 92697, USA
36 Center for Information Technology (CIT), University of Groningen, Groningen, The Netherlands
37 Poznan Supercomputing and Networking Center (PCSS) Poznan, Poland
38 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
39 Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501, Bielefeld, Germany
40 Department of Physics and Elelctronics, Rhodes University, PO Box 94, Grahamstown 6140, South Africa
41 SKA South Africa, 3rd Floor, The Park, Park Road, Pinelands, 7405, South Africa
42 International Centre for Radio Astronomy Research - Curtin University, GPO Box U1987, Perth, WA 6845, Australia
43 Jagiellonian University, Astronomical Observatory, Orla 171, 30-244 Krakow, Poland
44 Department of Physics and Electrical Engineering, Linnaeus University 35195, Vaexjoe, Sweden
Accepted: 24 March 2018
Context. Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20–90 MHz) is now possible with the Low Frequency Array (LOFAR), opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs.
Aims. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon.
Methods. Thetype II shock source-positions and spectra were obtained using 91 simultaneous tied-array beams of LOFAR, and the CME was observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) and by the COR2A coronagraph of the SECCHI instruments on board the Solar Terrestrial Relation Observatory(STEREO). The 3D structure was inferred using triangulation of the coronographic observations. Coronal magnetic fields were obtained from a 3D magnetohydrodynamics (MHD) polytropic model using the photospheric fields measured by the Heliospheric Imager (HMI) on board the Solar Dynamic Observatory (SDO) as lower boundary.
Results. The type II radio source of the coronal shock observed between 50 and 70 MHz was found to be located at the expanding flank of the CME, where the shock geometry is quasi-perpendicular with θBn ~ 70°. The type II radio burst showed first and second harmonic emission; the second harmonic source was cospatial with the first harmonic source to within the observational uncertainty. This suggests that radio wave propagation does not alter the apparent location of the harmonic source. The sources of the two split bands were also found to be cospatial within the observational uncertainty, in agreement with the interpretation that split bands are simultaneous radio emission from upstream and downstream of the shock front. The fast magnetosonic Mach number derived from this interpretation was found to lie in the range 1.3–1.5. The fast magnetosonic Mach numbers derived from modelling the CME and the coronal magnetic field around the type II source were found to lie in the range 1.4–1.6.
Key words: Sun: corona / Sun: coronal mass ejections (CMEs) / Sun: radio radiation
© ESO 2018
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