A stochastic model for solar type III bursts
Abstract
A stochastic model for type III bursts is introduced, discussed, and compared to observations. The active region is assumed to be inhomogeneous, with a large number of emerging magnetic fibers. At their bases, random energy release events take place, in the course of which electrons are accelerated, travel along the fibers and eventually undergo the bumpontail instability. In the nonlinear regime, the formed Langmuir waves induce strong turbulence in the ambient plasma, with secondary electrostatic waves appearing. Wavewave scattering finally leads to the emission of transverse electromagnetic waves at the fundamental and the harmonic of the local plasmafrequency. The superposition of the emissions from all the fibers yields a model spectrogram for type III bursts (flux as a function of frequency and time). Peakflux distributions of the model are compared to the ones of five observations of type III bursts. It turns out that, in a statistical sense, the model is largely compatible with the observations: the majority of the observations can be considered generated by a process which corresponds with the presented model. The details of the different subprocesses constituting the model play no decisive role concerning the statistical properties of the generated spectrograms, to describe them approximately by randomizing the unknown elements is sufficient. Therewith, the correspondence of the model with the data is not unique. Likewise, intrinsic shortness of observed type III events does not allow a strict enough discrimination between different possible subprocesses of the model through statistical tests. With that, the conclusion is that the observations are compatible with a model which assumes (i) a randomly structured active region, (ii) a flareparticle accelerationprocess which is fragmented into a large number of subprocesses, (iii) a distribution of the accelerated particles which is a random fraction of the ambient density and of powerlaw form with random index, and (iv) the fragmentary acceleration events to occur randomly in time, i.e. the temporal structure of type III events to be random, without any correlations between the individual bursts.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 August 1998
 Bibcode:
 1998A&A...336..371I
 Keywords:

 ACCELERATION OF PARTICLES;
 CHAOS;
 WAVES;
 METHODS: DATA ANALYSIS;
 SUN: FLARES;
 SUN: RADIO RADIATION