1998A&A...334.1099T

This paper reports the first comparison of hard X-ray (HXR), gamma-ray (GR), centimetric-millimetric and metric-decimetric spectral and imaging radio observations obtained during an electron-dominated gamma-ray burst. This impulsive event,which occurred on 1990 June 11 at ∼0943UT, was associated with a H_α 2B flare, located close to the disk center. The time evolution of the HXR emission consists of successive peaks of ∼10s duration. Several of these peaks show GR emission up to a few MeV and one of them up to ∼56MeV. For each of these peaks, the photon spectrum significantly hardens above a break energy varying in the 0.4-0.7MeV 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 >1MeV/nucl. ions is comparable with the energy content in >20keV electrons (a few 10²⁹ergs), as it is found for GRL flares; (ii) during the whole event, the centimetric-millimetric emission is radiated by >0.4-0.7MeV electrons which have been accelerated since the very beginning of the flare; (iii) the different HXR/GR peaks are associated with step-wise changes of the magnetic structures to which metric-decimetric radio producing electrons have access. This latter characteristic of the 1990 June 11 burst is globally similar to the behaviour reported in the literature for GRL events, but the energy in accelerated particles is about one order of magnitude lower. Finally, the electron-dominated emitting peak with emission up to ∼ 56 MeV is interpreted as a signature of an upward moving population of relativistic electrons which is strongly beamed along the magnetic field and which does not contribute significantly to the centimetric-millimetric and ≲0.2MeV HXR emissions. The metric-decimetric radio observations indicate that this happens when electrons have suddenly access to large-scale magnetic structures.