Abstract. A two-component (core-halo) emission model has been applied reconciling hard and soft X-ray burst emissions with the microwave burst radiation. The core region is represented by a nonthermal energy distribution (Maxwellian+power law tail) and assumed to be surrounded by a thermal halo. Parameters characterizing the energy distribution and emission measures have been derived numerically from soft and hard X-ray measurements. Using an artificial magnetic field model the microwave flux spectrum has been calculated on the basis of gyro-synchrotron emission and absorption by solving the equation of radiation transfer along the ray trajectories. Open parameters were used to adapt the spectrum to the radio measurements.Thus probable informations about the most appropriate magnetic field parameters as well as about the time-and frequency-dependent source diameters (yielding growth velocities of the core region during the impulsive phase) are deduced for the burst of 1972 May 18 as an example. A fit of the observed spectrum at the burst maximum is consistent with a magnetic field of 1500 G at the core centre decreasing up to about 40 G at the top of the halo at a height of 50 000 km above the centre, a core density of 1020 cm -3 decreasing to 109 cm -3 at the outer halo boundary, and a core diameter of 15 000 km (-20").Due to the simple geometry and emission process adopted,-the model refers primarily to special impulsive bursts. For the representation of broad band microwave bursts, e.g. type IV/x events, a more complex source geometry and/or other variants of the emission mechanism must be invoked.

The February 5, 1986 flare-related radio continuum depression is studied, compared with other noise storm depression events and discussed in the framework of current type I storm models. The influence of flare plasma flow or shocks and of superthermal electrons on noise storm radiation is considered. The presence of fast drifting emission features just before and during the decrease of the intensity, the association between the depression onset and the microwave burst maximum, the simultaneous appearance of the intensity minimum over a broad spectral range as well as preflare evidence of an interconnection of the flare site and the noise storm source are arguments for a preference of the role of beams of superthermal electrons. We distinguish abrupt and slow depressions ( Figure 5). The abrupt depressions are in agreement with Melrose's (1980) predictions. Slow depressions can only be understood by invoking the diffusion of superthermal electrons through the magnetic field carrying the storm source.

The type IV burst phenomenon consists of at least five physically distinct components or phases. Concerning the spectral and polarization characteristics of the radio emission, the X-ray emission and the association of energetic particle emission, two main classes of type IV burst components can be distinguished. The first class associated with energetic particle events comprises the (especially hard) X-ray burst, the type 1V/z and mA1 components. With respect to the dynamics of the burst source a 'quasistationary' mAl-phase can be distinguished from a 'moving' mA2-phase. The general tendencies of the development of large type IV events have been discussed with regard to the possibility of the occurrence of neutral points of the magnetic field in greater coronal heights.

No abstract

No abstract