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| Paper: |
The Nature of Loop-Top Sources in Solar X-ray Flares |
| Volume: |
154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop |
| Page: |
671 |
| Authors: |
Phillips, K. J. H.; Jakimiec, J.; Tomczak, M.; Falewicz, R.; Fludra, A. |
| Abstract: |
Bright, compact loop-top sources or kernels are a conspicuous feature of soft X-ray flares as imaged by the SXT instrument on the Japanese solar mission Yohkoh, and their nature has been widely discussed. We have done a detailed comparison of the observations from the hard and soft X-ray imaging instruments (HXT and SXT) as well as the Bragg Crystal Spectometer (BCS) on Yohkoh for some 36 flares. We find evidence that the loop-top sources in these flares are highly non-isothermal, with temperature ranging from ~10 MK (as seen by SXT) to ~20 MK or more (as deduced from line ratios in the BCS range and the presence of gradually varying emission in the HXT 14-23 keV energy band). The SXT temperature maps (formed from the ratio of emission through two different filters) show that the temperature distribution within the loop-top source is uniform. We argue that the most plausible model to explain this is one in which the loop-top source is made up of highly tangled magnetic field lines, where current sheets continually form, supplying energy to the region. Both freshly heated plasma (~20 MK) and cooled plasma (~10 MK) co-exist in the same region. A calculation of the energy balance of the loop-top region suggests that the heating is not uniform within the region but rather is at a maximum near its edge. This may be explained by the reconnection of the tangled field with the field of the loop legs, which has a simple geometry. |
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