1 Max-Planck-Institut fuer extraterrestrishe Physik

2 Astronomical Institute, 251 65 Ondrejov, Czech Republic

Radio-silent gamma-ray flares are solar flares that lack any significant emission in the (non-thermal) radio wave band during their impulsive hard X-ray and gamma-ray emission phases. A striking example of a radio-silent flare was observed by SMM during the onset of the March 6, 1989 energetic gamma-ray flare. We argue that the absence of radio emission at wave-lengths longer than microwave wavelengths is an indication of the compactness of the flare rather than that the flare did not exhibit non-thermal properties. Probably the flare site was restricted to very low altitudes above the photosphere in a newly emerging loop configuration. Reconnection in such a configuration did not lead to open magnetic fields and streamer formation. Acceleration of particles in the gamma- and X-ray bursts was restricted to closed field lines. The emission during the first energetic burst was dominated by a continuum originating from electron bremsstrahlung at X-ray and gamma-ray energies with only little evidence for the presence of gamma-ray lines. It is shown that the high density of the plasma, where particle acceleration took place cannot have been the reason that the event got electron-dominated.