LOFAR tied-array imaging of Type III solar radio bursts

D. E. Morosan P. T. Gallagher 1 P. Zucca R. Fallows E. P. Carley G. Mann 2 M. M. Bisi 3 A. Kerdraon 4 A. A. Konovalenko 5 A. L. Mackinnon 6 H. O. Rucker 7 B. Thidé 8 J. Magdalenić C. Vocks 2 H. Reid J. Anderson A. Asgekar I. M. Avruch 9 M. J. Bentum G. Bernardi P. Best A. Bonafede 10 J. Bregman F. Breitling J. Broderick 11 M. Brüggen 10 H. R. Butcher 12 B. Ciardi 13 J. E. Conway F. de Gasperin 14 E. de Geus A. Deller 15 S. Duscha J. Eislöffel 16 D. Engels 14 H. Falcke 17 C. Ferrari 18 W. Frieswijk 15 M. A. Garrett 19 Jean-Mathias Grießmeier 20, 21 A. W. Gunst T. E. Hassall J. W. T. Hessels M. Hoeft 16 J. Hörandel 17 A. Horneffer M. Iacobelli 19 E. Juette 22 A. Karastergiou V. I. Kondratiev 15 M. Kramer M. Kuniyoshi 23 G. Kuper 15 P. Maat S. Markoff 24 J. P. Mckean 15 D. D. Mulcahy 11 H. Munk A. Nelles 17 M. J. Norden 15 E. Orru 15 H. Paas M. Pandey-Pommier 25 V. N. Pandey 26 G. Pietka R. Pizzo 15 A. G. Polatidis 15 W. Reich 23 H. Röttgering 19 A. M. M. Scaife 27 D. Schwarz M. Serylak O. Smirnov B. W. Stappers A. Stewart 28 Michel Tagger 21 Y. Tang 29 C. Tasse 4 S. Thoudam 17 C. Toribio 15 R. Vermeulen 15 R. J. Van Weeren 30 O. Wucknitz S. Yatawatta 15 P. Zarka 4
Abstract : The Sun is an active source of radio emission which is often associated with energetic phenomena such as solar flares and coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), the Sun has not been imaged extensively because of the instrumental limitations of previous radio telescopes. Here, the combined high spatial, spectral and temporal resolution of the Low Frequency Array (LOFAR) was used to study solar Type III radio bursts at 30-90 MHz and their association with CMEs. The Sun was imaged with 126 simultaneous tied-array beams within 5 solar radii of the solar centre. This method offers benefits over standard interferometric imaging since each beam produces high temporal (83 ms) and spectral resolution (12.5 kHz) dynamic spectra at an array of spatial locations centred on the Sun. LOFAR's standard interferometric output is currently limited to one image per second. Over a period of 30 minutes, multiple Type III radio bursts were observed, a number of which were found to be located at high altitudes (4 solar radii from the solar center at 30 MHz) and to have non-radial trajectories. These bursts occurred at altitudes in excess of values predicted by 1D radial electron density models. The non-radial high altitude Type III bursts were found to be associated with the expanding flank of a CME. The CME may have compressed neighbouring streamer plasma producing larger electron densities at high altitudes, while the non-radial burst trajectories can be explained by the deflection of radial magnetic fields as the CME expanded in the low corona.
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D. E. Morosan, P. T. Gallagher, P. Zucca, R. Fallows, E. P. Carley, et al.. LOFAR tied-array imaging of Type III solar radio bursts. Astronomy and Astrophysics - A&A, EDP Sciences, 2014, 568 (A67), ⟨10.1051/0004-6361/201423936⟩. ⟨insu-01336001⟩

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