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Hard X-Ray Imaging Observations by Yohkoh of the 15 November, 1991 Flare

Published online by Cambridge University Press:  12 April 2016

Taro Sakao
Taro Sakao*
Affiliation:
National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181, Japan

Abstract

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We present hard X-ray imaging observations by Yohkoh of the 15 November, 1991 flare. The pre-impulsive and the impulsive phase observations are summarized as follows: (1) Hard X-ray sources in the precursor (or pre–impulsive) phase appear in a much wider area compared with the impulsive phase sources and they show clear evolution just before the onset of the impulsive phase. This suggests that some global re-structuring of coronal magnetic fields led to the impulsive energy release. (2) In the impulsive phase, at the peaks of the individual spikes of the time profile, the bulk of the hard X-ray emission (above 20 keV) originates from the footpoints of the flaring loop. At the valleys between the spikes, X-rays below 30 keV are emitted from near the loop top, while higher energy ones (above 30 keV) are still emitted from the footpoints. Such behavior of hard X-ray sources can be explained by the partial precipitation model.

Type
Session 5. Fields in the Chromosphere and Corona
Information
International Astronomical Union Colloquium , Volume 141: The Magnetic and Velocity Fields of Solar Active Regions , 1993 , pp. 258 - 262
Copyright
Copyright © Astronomical Society of the Pacific 1993

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