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Astron. Astrophys. 334, 289-298 (1998)

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The 09 September 1989 [FORMULA] -ray flare - multi-site particle acceleration and shock-excited radio emission during quasiperpendicular and quasiparallel propagation

H. Aurass 1, A. Hofmann 1 and H.-W. Urbarz * 2

1 Astrophysikalisches Institut Potsdam, Observatorium für solare Radioastronomie und Sonnenobservatorium Einsteinturm,
An der Sternwarte 16, D-14482 Potsdam, Germany
2 Universität Tübingen, Aussenstelle Datenarchiv Weissenau, D-7980 Ravensburg, Germany

Received 6 October 1997 / Accepted 16 February 1998


This is a case study of the location of particle acceleration sites during an impulsive flare and its subsequent coronal shock which occurred on 09 September 1989. Joint radio, hard X-ray/ [FORMULA] -ray, and [FORMULA] observations of the flare impulsive emissions reveal that electron and ion acceleration results from successive energy release in different magnetic structures. In this paper we attempt to identify these magnetic structures, during both the impulsive flare and the coronal shock propagation. This is done by tracing essential features identified in high time resolution radio spectral and hard X-ray/ [FORMULA] -ray data in radio images, and comparing the spatial information with sequences of [FORMULA] images and a static figure of the coronal magnetic field lines derived by extrapolating photospheric field measurements. During the impulsive phase signatures of energy release are found in different coronal height ranges which are magnetically connected with a small part of an underlying active region that is invaded by an expanding [FORMULA] flare ribbon. The magnetic field configuration comprises two sites at heights between 2 [FORMULA] 104 and 8 [FORMULA] 104 km above the primary highly confined flare. These sites are characterized by coronal magnetic field line systems crossing at nearly right angle. This provides for potential sites of efficient energy release and particle acceleration without demanding for extreme twist. The subsequent shock wave, revealed by type II radio burst emission, is found to propagate over large distances ([FORMULA] 1 [FORMULA]) through the corona and to accelerate electrons in regions where it propagates along and across the ambient magnetic field.

Key words: Sun: radio radiation – Sun: magnetic fields – Sun: flares – Sun: X-rays, gamma-rays – shock waves

* Hans Walter Urbarz passed away on 23 July 1996.

Send offprint requests to: H. Aurass

© European Southern Observatory (ESO) 1998

Online publication: May 12, 1998