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Astron. Astrophys. 334, 1099-1111 (1998)

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A multiwavelength analysis of an electron-dominated gamma-ray event associated with a disk solar flare

Gérard Trottet 1, Nicole Vilmer 1, Claude Barat 2, Arnold Benz 3, Andreas Magun 4, Alexandr Kuznetsov 5, Rachid Sunyaev 5 and Oleg Terekhov 5

1 DASOP, CNRS-URA 2080, Observatoire de Paris, Section de Meudon, F-92195 Meudon, France
2 Centre d'Etude Spatiale des Rayonnements, BP 4346, F-31029 Toulouse, France
3 Institute of Astronomy, ETH-Zentrum, CH-8092 Zürich, Switzerland
4 University of Bern, IAP, Sidlerstrasse 5, CH-3012 Bern, Switzerland
5 Space Science Institute, Profsoyouznaya 84/32, 117810 Moscow, Russia

Received 19 November 1997 / Accepted 6 March 1998

Abstract

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 [FORMULA] 0943 UT, was associated with a [FORMULA] 2B flare, located close to the disk center. The time evolution of the HXR emission consists of successive peaks of [FORMULA] 10 s duration. Several of these peaks show GR emission up to a few MeV and one of them up to [FORMULA] 56 MeV. For each of these peaks, the photon spectrum significantly hardens above 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 [FORMULA] 1MeV/nucl. ions is comparable with the energy content in [FORMULA] 20 keV electrons (a few 1029 ergs), as it is found for GRL flares; (ii) during the whole event, the centimetric-millimetric emission is radiated by [FORMULA] 0.4-0.7 MeV 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 [FORMULA] 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 [FORMULA] 0.2 MeV HXR emissions. The metric-decimetric radio observations indicate that this happens when electrons have suddenly access to large-scale magnetic structures.

Key words: Sun: activity – Sun: flares – Sun: particle emission – Sun: radio radiation

Send offprint requests to: G. Trottet

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© European Southern Observatory (ESO) 1998

Online publication: June 2, 1998

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