Tracking of an electron beam through the solar corona with LOFAR

¹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: GMann@aip.de, frank.breitling@gmx.de
² RAL Space, Science & Technology Facilities Council (STFC) – Rutherford Appleton Laboratory (RAL), Harwell Oxford, Oxfordshire, OX11 0QX, UK
³ ASTRON, Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁴ Astrophysics Research Group, School of Physics, Trinity College Dublin, Dublin 2, Ireland
⁵ LESIA & USN, Observatoire de Paris, CNRS, PSL/SU/UPMC/UPD/SPC, Place J. Janssen, 92195 Meudon, France
⁶ SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK
⁷ Solar-Terrestrial Center of Excellence, SIDC, Royal Observatory of Belgium, Avenue Circulaire 3, 1180 Brussels, Belgium
⁸ Space Research Institute, Austrian Academy of Sciences, Schmiedl Strasse 6, 8042 Graz, Austria
⁹ Helmholtz-Zentrum Potsdam, Deutsches GeoForschungs Zentrum GFZ, Department 1: Geodesy and Remote Sensing, Telegrafenberg, A17, 14473 Potsdam, Germany
¹⁰ Shell Technology Center, Bangalore, India
¹¹ SRON Netherlands Insitute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
¹² Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
¹³ CSIRO Australia Telescope National Facility, PO Box 76, Epping NSW 1710, Australia
¹⁴ University of Twente, Enschede, The Netherlands
¹⁵ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
¹⁶ Institute for Astronomy, University of Edinburgh, Royal Observatory of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
¹⁷ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁸ University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁹ School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
²⁰ Research School of Astronomy and Astrophysics, Australian National University, Mt Stromlo Obs., via Cotter Road, Weston, A.C.T. 2611, Australia
²¹ Max Planck Institute for Astrophysics, Karl Schwarzschild Str. 1, 85741 Garching, Germany
²² Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands
²³ SmarterVision BV, Oostersingel 5, 9401 JX Assen, The Netherlands
²⁴ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
²⁵ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
²⁶ Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
²⁷ Laboratoire Lagrange, UMR7293, Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, 06300 Nice, France
²⁸ LPC2E – Université d’Orléans/CNRS, France
²⁹ Station de Radioastronomie de Nançay, Observatoire de Paris – CNRS/INSU, USR 704 – Univ. Orléans, OSUC, route de Souesmes, 18330 Nançay, France
³⁰ Anton Pannekoek Institute, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
³¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³² Astronomisches Institut der Ruhr-Universität Bochum, Universitaetsstrasse 150, 44780 Bochum, Germany
³³ Astro Space Center of the Lebedev Physical Institute, Profsoyuznaya str. 84/32, 117997 Moscow, Russia
³⁴ Jodrell Bank Center for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK
³⁵ Sodankylä Geophysical Observatory, University of Oulu, Tähteläntie 62, 99600 Sodankylä, Finland
³⁶ STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot OX11 0QX, UK
³⁷ Center for Information Technology (CIT), University of Groningen, Groningen, The Netherlands
³⁸ Centre de Recherche Astrophysique de Lyon, Observatoire de Lyon, 9 Av. Charles André, 69561 Saint-Genis-Laval Cedex, France
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

Received: 27 May 2016
Accepted: 14 November 2017

Abstract

The Sun’s activity leads to bursts of radio emission, among other phenomena. An example is type-III radio bursts. They occur frequently and appear as short-lived structures rapidly drifting from high to low frequencies in dynamic radio spectra. They are usually interpreted as signatures of beams of energetic electrons propagating along coronal magnetic field lines. Here we present novel interferometric LOFAR (LOw Frequency ARray) observations of three solar type-III radio bursts and their reverse bursts with high spectral, spatial, and temporal resolution. They are consistent with a propagation of the radio sources along the coronal magnetic field lines with nonuniform speed. Hence, the type-III radio bursts cannot be generated by a monoenergetic electron beam, but by an ensemble of energetic electrons with a spread distribution in velocity and energy. Additionally, the density profile along the propagation path is derived in the corona. It agrees well with three-fold coronal density model by (1961, ApJ, 133, 983).