Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR

P. Zucca 1 D. Morosan 2 P. Rouillard 3 R. Fallows 4 P. Gallagher 5 J. Magdalenic 6 K.-L. Klein 7 G. Mann 8 C. Vocks 8 P. Carley M. Bisi 9 P. Kontar 10 H. Rothkaehl 11 B. Dabrowski 12 A. Krankowski 13 J. Anderson 14 A. Asgekar 1 M. Bell M. Bentum 1 P. Best R. Blaauw 1 F. Breitling 8 J. Broderick 15 W. Brouw 16 M. Bruggen 17 R. Butcher B. Ciardi 18 E. Geus A. Deller 1 S. Duscha 1 J. Eisloffel 19 M. Garrett 20 M. Grießmeier A. Gunst 1 G. Heald 1 M. Hoeft 19 J. Hörandel 21 M. Iacobelli 20 E. Juette 22 A. Karastergiou 23 J. Leeuwen 1 D. Mckay-Bukowski 24 H. Mulder H. Munk 1 A. Nelles 21 E. Orru 1 H. Paas 1 V. Pandey 25 R. Pekal R. Pizzo 1 A. Polatidis 1 W. Reich 26 A. Rowlinson 1 J. Schwarz A. Shulevski 27 J. Sluman 1 O. Smirnov C. Sobey 26 M. Soida S. Thoudam 21 M. Toribio R. Vermeulen 28 R. Van Weeren 1 O. Wucknitz 29 P. Zarka 30 Jean-Mathias Griessmeier 31, 32
Abstract : 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.
Type de document :
Article dans une revue
Astronomy and Astrophysics - A&A, EDP Sciences, 2018, 615 (A89), 〈10.1051/0004-6361/201732308〉
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Soumis le : mardi 28 août 2018 - 09:42:59
Dernière modification le : jeudi 7 février 2019 - 16:06:43

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P. Zucca, D. Morosan, P. Rouillard, R. Fallows, P. Gallagher, et al.. Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR. Astronomy and Astrophysics - A&A, EDP Sciences, 2018, 615 (A89), 〈10.1051/0004-6361/201732308〉. 〈insu-01862977〉



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