LOFAR tied-array imaging and spectroscopy of solar S bursts
Journal
Date Issued
2015
Author(s)
Morosan, D. E.
•
Gallagher, P. T.
•
Zucca, P.
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O'Flannagain, A.
•
Fallows, R.
•
Reid, H.
•
Magdalenić, J.
•
Mann, G.
•
Bisi, M. M.
•
Kerdraon, A.
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Konovalenko, A. A.
•
MacKinnon, A. L.
•
Rucker, H. O.
•
Thidé, B.
•
Vocks, C.
•
Alexov, A.
•
Anderson, J.
•
Asgekar, A.
•
Avruch, I. M.
•
Bentum, M. J.
•
•
Bonafede, A.
•
Breitling, F.
•
Broderick, J. W.
•
Brouw, W. N.
•
Butcher, H. R.
•
Ciardi, B.
•
de Geus, E.
•
Eislöffel, J.
•
Falcke, H.
•
Frieswijk, W.
•
Garrett, M. A.
•
Grießmeier, J.
•
Gunst, A. W.
•
Hessels, J. W. T.
•
Hoeft, M.
•
Karastergiou, A.
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Kondratiev, V. I.
•
Kuper, G.
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van Leeuwen, J.
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McKay-Bukowski, D.
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McKean, J. P.
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Munk, H.
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Orru, E.
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Paas, H.
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Pizzo, R.
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Polatidis, A. G.
•
Scaife, A. M. M.
•
Sluman, J.
•
Tasse, C.
•
Toribio, M. C.
•
Vermeulen, R.
•
Zarka, P.
Description
This work has been supported by a Government of Ireland studentship from the Irish Research Council (IRC), the Non-Foundation Scholarship awarded by Trinity College Dublin, the Innovation Academy and the IRC New Foundations. Hamish Reid is supported by a SUPA Advanced Fellowship and an STFC grant ST/L000741/1. We would finally like to acknowledge the LOFAR telescope. LOFAR, the LOw Frequency ARray designed and constructed by ASTRON, has facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the International LOFAR Telescope (ILT) foundation under a joint scientific policy.
Abstract
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 h. 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-1 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. A movie associated to Fig. 3 is available in electronic form at "http://www.aanda.org/10.1051/0004-6361/201526064/olm"
Volume
580
Start page
A65
Issn Identifier
0004-6361
Ads BibCode
2015A&A...580A..65M
Rights
open.access
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