Tracking of an electron beam through the solar corona with LOFAR

The Sun's activity leads to burstsof radio emission, among other phenomena. An example is type-III radio bursts. They occur frequently and appear as short-lived structures rapidly drifting from high to low frequencies in dynamic radio spectra. They are usually interpreted as signatures of beams of energetic electrons propagating along coronalmagnetic field lines. Here we present novel interferometric LOFAR(LOw Frequency ARray) observations of three solar type-III radio burstsand their reverse burstswith high spectral, spatial, and temporal resolution. They are consistent with a propagation of the radio sources along the coronalmagnetic field lineswith nonuniform speed. Hence, the type-III radio burstscannot be generated by a monoenergetic electron beam, but by an ensemble of energetic electrons with a spread distribution in velocity and energy. Additionally, the density profile along the propagation path is derived in the corona. It agrees well with three-fold coronaldensity model by (1961, ApJ, 133, 983).