First observation of the solar Type III burst decay and its interpretation

TL;DR

This paper reports the first observation of a solar Type III burst decay into two bursts, confirming predictions of a gas-dynamic theory involving high-energy electron beams and providing detailed velocity and density ratio measurements.

Contribution

It presents the first observational evidence of Type III burst decay and interprets it using a gas-dynamic model of electron beam propagation in plasma.

Findings

Decay of Type III burst into two bursts observed for the first time

Newborn Type III bursts have smaller drift rates than decaying burst

Velocities of sources and density ratios are quantified

Abstract

A decay of Type III burst into two Type III bursts was registered during solar observations by GURT and URAN-2 radio telescopes on April 18, 2017. Such phenomenon was observed for the first time. Newborn Type III bursts have drift rates smaller than that of decaying Type III burst. Such decays of Type III bursts were predicted by a gas-dynamic theory of high-energy electron beams propagating through the thermal background plasma. In the frame of this theory Type III sources are beam-plasma structures moving with constant velocities. In our case the sum of velocities of newborn Type III sources equals the velocity of decaying Type III source. The last one is 0.33c in the case of fundamental radio emission and 0.2c at the harmonic radio emission of Type III burst. The density ratio of slow and fast newborn Type III sources is about 3.