Electron acceleration sites in a large-scale coronal structure

Klein, K.-L. and Aurass, H. and Soru-Escaut, I. and Kálmán, Béla (1997) Electron acceleration sites in a large-scale coronal structure. Astronomy and Astrophysics, 320. pp. 612-619. ISSN 0004-6361

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Abstract

Radio observations and interplanetary particle measurements have shown that even in the absence of conspicuous violent processes in the low atmosphere (such as Hα flares) electrons are accelerated in the corona, most likely at higher altitudes than during flares (≥0.5 R above the photosphere). The paper presents direct evidence on the acceleration sites from a case study of radio, visible light and soft X-ray observations: electrons are repeatedly accelerated in a large-scale coronal structure which is identified with a streamer in coronographic observations. Energy is simultaneously released in an active region near the base of the structure and at a height of ∼1 R , over several hours before the large-scale structure erupts. Energy input is observed in at least two emerging active regions underneath the streamer. The coronal configuration is three-dimensional, overlying a whole quadrant of the Sun. It is argued that the observations trace multiple sites of energy release presumably in current sheets embedded within the streamer, in agreement with scenarios developed for the acceleration of electrons seen in the corona and at 1 AU, and for the evolution of large-scale coronal structures towards eruption.

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