A MULTIWAVELENGTH ANALYSIS OF AN ELECTRON-DOMINATED GAMMA-RAY EVENT ASSOCIATED WITH A DISK SOLAR-FLARE

This paper reports the first comparison of hard X-ray (HXR), gamma-ray (GR), centimetric-millimetric and metric-decimetric spectral and imag ing radio observations obtained during an electron-dominated gamma-ray burst. This impulsive event,which occurred on 1990 June 11 at similar to 0943 UT, was associated with a H-alpha 2B flare, located close to the disk center. The time evolution of the HXR emission consists of su ccessive peaks of similar to 10 s duration. Several of these peaks sho w GR emission up to a few MeV and one of them up to similar to 56 MeV. For each of these peaks, the photon spectrum significantly hardens ab ove a break energy varying in the 0.4-0.7 MeV range. No significant GR line (GRL) emission is detected. The main results of our analysis are : (i) even if no significant GRL emission is detected, the upper limit of the energy content in > 1 MeV/nucl. ions is comparable with the en ergy content in > 20 keV electrons ( a few 10(29) ergs), as it is foun d for GRL flares; (ii) during the whole event, the centimetric-millime tric emission is radiated by greater than or similar to 0.4-0.7 MeV el ectrons which have been accelerated since the very beginning of the fl are; (iii) the different HXR/GR peaks are associated with step-wise ch anges of the magnetic structures to which metric-decimetric radio prod ucing electrons have access. This latter characteristic of the 1990 Ju ne 11 burst is globally similar to the behaviour reported in the liter ature for GRL events, but the energy in accelerated particles is about one order of magnitude lower. Finally, the electron-dominated emittin g peak with emission up to similar to 56 MeV is interpreted as a signa ture of an upward moving population of relativistic electrons which is strongly beamed along the magnetic field and which does not contribut e significantly to the centimetric-millimetric and less than or simila r to 0.2 MeV HXR emissions. The metric-decimetric radio observations i ndicate that this happens when electrons have suddenly access to large -scale magnetic structures.