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LOFAR tied-array imaging and spectroscopy of solar S bursts | | 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
; | | Date: |
27 Jul 2015 | | 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 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. | | Source: | arXiv, 1507.7496 | | Services: | Forum | Review | PDF | Favorites | |
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