During a solar eruption, accelerated electrons cause the solar corona to produce intense bursts of radio radiation. Recent observations using the largest decametre radio telescopes (LOFAR, URAN-2) have allowed us, for the first time, to study the detailed time history of the fine structures of solar radio burst sources on tens of millisecond time scales.
We have found that very small radio sources rapidly grow in size because of scattering of the radio waves in the surrounding atmosphere, leading to an apparent size that is thousand times larger than the actual region where the radio waves are produced. As a result, we now have a much better understanding of the physical conditions in the source of the radio waves, and we have also learned about the nature of the turbulence that causes the sources to grow so quickly.
The observations with high time resolution provide a new opportunity for diagnostics of small-scale plasma fluctuations -- imaging the radio source halos as the radio waves move in the solar corona. These results permit more accurate estimates of source brightness temperatures, and open opportunities for quantitative study of the mechanisms that create the turbulent coronal medium through which the emitted radiation propagates.
LOFAR is the Low Frequency Array designed and constructed by ASTRON, The Netherlands. It has facilities in several countries including France, Germany, Sweden, Poland and the UK.
Reference: Imaging spectroscopy of solar radio burst fine structures; Nature Communications, November (2017).