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* News 04/04/20 * The archive is using a new backend database. This has thrown up a few SQL errors in the last few days. If you have any issues please email adavey@nso.edu with either the number of eprint you are trying to edit or a link to your preprint.

Variable emission mechanism of a Type IV radio burst  

Diana Morosan   Submitted: 2019-03-15 04:01

Context. The Sun is an active star and the source of the largest explosions in the solar system, such as flares and coronal mass ejections (CMEs). Flares and CMEs are powerful particle accelerators that can generate radio emission through various emission mechanisms. Aims. CMEs are often accompanied by Type IV radio bursts that are observed as continuum emission in dynamic spectra at decimetric and metric wavelengths, but their emission mechanism can vary from event to event. Here, we aim to determine the emission mechanism of a complex Type IV burst that accompanied the flare and CME on 22 September 2011. Methods. We used radio imaging from the Nançay Radioheliograph, spectroscopic data from the e-Callisto network, ARTEMIS, Ondřejov;, and Phoenix3 spectrometers combined with extreme-ultraviolet observations from NASA's Solar Dynamic Observatory to analyse the Type IV radio burst and determine its emission mechanism. Results. We show that the emission mechanism of the Type IV radio burst changes over time. We identified two components in the Type IV radio burst: an earlier stationary Type IV showing gyro-synchrotron behaviour, and a later moving Type IV burst covering the same frequency band. This second component has a coherent emission mechanism. Fundamental plasma emission and the electroncyclotron maser emission are further investigated as possible emission mechanisms for the generation of the moving Type IV burst. Conclusions. Type IV bursts are therefore complex radio bursts, where multiple emission mechanisms can contribute to the generation of the wide-band continuum observed in dynamic spectra. Imaging spectroscopy over a wide frequency band is necessary to determine the emission mechanisms of Type IV bursts that are observed in dynamic spectra.

Authors: D. E. Morosan, E. K. J. Kilpua, E. P. Carley, and C. Monstein
Projects: Nançay Radioheliograph

Publication Status: Published
Last Modified: 2019-03-17 18:53
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LOFAR tied-array imaging and spectroscopy of solar S bursts  

Diana Morosan   Submitted: 2015-07-28 08:34

Context. The Sun is an active source of radio emission that is often associated with energetic phenomena ranging from nanoflares to coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), numerous millisecond duration radio bursts have been reported, such as radio spikes or solar S bursts (where S stands for short). To date, these have neither been studied extensively nor imaged because of the instrumental limitations of previous radio telescopes. Aims. Here, Low Frequency Array (LOFAR) observations were used to study the spectral and spatial characteristics of a multitude of S bursts, as well as their origin and possible emission mechanisms. Methods. We used 170 simultaneous tied-array beams for spectroscopy and imaging of S bursts. Since S bursts have short timescales and fine frequency structures, high cadence (~50 ms) tied-array images were used instead of standard interferometric imaging, that is currently limited to one image per second. Results. On 9 July 2013, over 3000 S bursts were observed over a time period of ~8 hours. S bursts were found to appear as groups of short-lived (<1 s) and narrow-bandwidth (~2.5 MHz) features, the majority drifting at ~3.5 MHz/s and a wide range of circular polarisation degrees (2-8 times more polarised than the accompanying Type III bursts). Extrapolation of the photospheric magnetic field using the potential field source surface (PFSS) model suggests that S bursts are associated with a trans-equatorial loop system that connects an active region in the southern hemisphere to a bipolar region of plage in the northern hemisphere. Conclusions. We have identified polarised, short-lived solar radio bursts that have never been imaged before. They are observed at a height and frequency range where plasma emission is the dominant emission mechanism, however they possess some of the characteristics of electron-cyclotron maser emission.

Authors: D. E. Morosan, P. T. Gallagher, P. Zucca, A. O'Flannagain, R. Fallows, H. Reid, J. Magdalenic, G. Mann, M. M. Bisi, A. Kerdraon, A. A. Konovalenko, A. L. MacKinnon, H. O. Rucker, B. Thide, C. Vocks, A. Alexov, J. Anderson, A. Asgekar, I. M. Avruch, M. J. Bentum, G. Bernardi, A. Bonafede, F. Breitling, J. W. Broderick, W. N. Brouw, H. R. Butcher, B. Ciardi, E. de Geus, J. Eisloffel, H. Falcke, W. Frieswijk, M. A. Garrett, J. Griessmeier, A. W. Gunst, J. W. T. Hessels, M. Hoeft, A. Karastergiou, V. I. Kondratiev, G. Kuper, J. van Leeuwen, D. McKay-Bukowski, J. P. McKean, H. Munk, E. Orru, H. Paas, R. Pizzo, A. G. Polatidis, A. M. M. Scaife, J. Sluman, C. Tasse, M. C. Toribio, R. Vermeulen, P. Zarka
Projects: Other

Publication Status: Accepted
Last Modified: 2015-07-29 13:00
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Variable emission mechanism of a Type IV radio burst
LOFAR tied-array imaging and spectroscopy of solar S bursts

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