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Astron. Astrophys. 334, 1112-1122 (1998)


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The bright loop-top kernels in Yohkoh X-ray flares

J. Jakimiec 1, M. Tomczak 1, R. Falewicz 1, K.J.H. Phillips 2 and A. Fludra 2

1 Astronomical Institute of the Wroclaw University, Kopernika 11, PL-51-622 Wroclaw, Poland
2 Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK

Received 24 April 1997 / Accepted 19 February 1998

Abstract

We have investigated loop-top kernels of the soft X-ray emission seen in the Yohkoh Soft X-ray Telescope (SXT) images. Detailed comparison of the observations from various Yohkoh instruments shows that these kernels contain two kinds of flare plasma: a cooler ([FORMULA] 10 MK) and a hotter ([FORMULA] 20 MK) one. The cooler plasma plays a dominant role in the emission recorded by the SXT and the hotter plasma is responsible for the Fe XXV emission and the emission recorded by Hard X-ray Telescope 14-23 keV band during the post-impulsive phase of a flare. We argue that the best model, which is in agreement with the above observational results, is a turbulent model of a flare loop-top kernel. The magnetic field is tangled in the kernel and a number of transient current sheets occur there. The hotter ([FORMULA] 20 MK) plasma is contained in the current sheets and they are surrounded by the cooler ([FORMULA] 10 MK) plasma. The turbulent model of the flare loop-top kernel also allows us to explain why the kernels are brighter than the "legs" connecting them with the chromosphere.

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

Send offprint requests to: M. Tomczak

© European Southern Observatory (ESO) 1998

Online publication: June 2, 1998

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