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Astron. Astrophys. 337, 911-920 (1998)

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Multi-wavelength observations of post flare loops in two long duration solar flares

L.K. Harra-Murnion 1, B. Schmieder 2, 3, L. van Driel-Gesztelyi 2, 4, J. Sato 5, S.P. Plunkett 6, P. Rudawy 7, B. Rompolt 7, M. Akioka 8, T. Sakao 5 and K. Ichimoto 5

1 Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
2 DASOP, Observatoire de Paris, F-92195 Meudon Principal Cedex, France
3 University of Oslo, P.O. Box 1029, Blindern, N-0315 Oslo, Norway
4 Konkoly Observatory, 1525 Budapest, P.O. 67, Hungary
5 National Astronomical Observatory, Mitaka, Tokyo 181, Japan
6 Universities Space Research Association, Naval Research Laboratory, Washington, DC 20375, USA
7 Astronomical Institute of Wroclaw University, ul. Kopernika 11, PL-51622 Wroclaw, Poland
8 Hiraiso Solar Terrestrial Research Center, Communications Research Laboratory, Isozaki, Nakaminato-shi, 311-12 Ibaraki, Japan

Received 9 April 1998 / Accepted 2 July 1998


We have analysed two Long Duration solar Events (LDEs) which produced large systems of Post Flare Loops (PFLs) and which have been observed by Yohkoh and ground-based observatories. Using the Maximum Entropy Method (MEM) image synthesis technique with new modulation patterns we were able to make hard X-ray (HXR) images of the post flare loops recorded in the L Channel (13.9-22.7 keV) of the Yohkoh Hard X-ray Telescope. We obtained co-aligned 2-D maps in H[FORMULA] (104 K), in soft X-rays (5[FORMULA] K) and in hard X-rays (20[FORMULA] K). We conclude that the soft X-ray (SXR) loops lie higher than the H[FORMULA] loops and the former are overlaid by HXR emission. This is suggestive of the magnetic reconnection process. However some details are not consistent with the standard models. Firstly the separation between the HXR source and the SXR loop increases with time, with the HXR source being approximately a factor of five larger than the equivalent source in impulsive flares. Secondly the cooling times deduced from observations are longer than the theoretically expected ones and the discrepancy increases with time. We review the current models in view of these results.

Key words: Sun: flares – Sun: X-rays, gamma rays

Send offprint requests to: L.K. Harra-Murnion

© European Southern Observatory (ESO) 1998

Online publication: August 27, 1998