A Quantitative Model of Energy Release and Heating by Time-dependent, Localized Reconnection in a Flare with Thermal Loop-top X-ray Source
Abstract
We present a quantitative model of the magnetic energy stored and then released through magnetic reconnection for a flare on 26 February 2004. This flare, well observed by RHESSI and TRACE, shows evidence of non-thermal electrons for only a brief, early phase. Throughout the main period of energy release there is a super-hot (T≳30 MK) plasma emitting thermal bremsstrahlung atop the flare loops. Our model describes the heating and compression of such a source by localized, transient magnetic reconnection. It is a three-dimensional generalization of the Petschek model, whereby Alfvén-speed retraction following reconnection drives supersonic inflows parallel to the field lines, which form shocks: heating, compressing, and confining a loop-top plasma plug. The confining inflows provide longer life than a freely expanding or conductively cooling plasma of similar size and temperature. Superposition of successive transient episodes of localized reconnection across a current sheet produces an apparently persistent, localized source of high-temperature emission. The temperature of the source decreases smoothly on a time scale consistent with observations, far longer than the cooling time of a single plug. Built from a disordered collection of small plugs, the source need not have the coherent jet-like structure predicted by steady-state reconnection models. This new model predicts temperatures and emission measure consistent with the observations of 26 February 2004. Furthermore, the total energy released by the flare is found to be roughly consistent with that predicted by the model. Only a small fraction of the energy released appears in the super-hot source at any one time, but roughly a quarter of the flare energy is thermalized by the reconnection shocks over the course of the flare. All energy is presumed to ultimately appear in the lower-temperature (T≲20 MK) post-flare loops. The number, size, and early appearance of these loops in TRACE's 171 Å band are consistent with the type of transient reconnection assumed in the model.
- Publication:
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Solar Physics
- Pub Date:
- November 2010
- DOI:
- 10.1007/s11207-010-9635-z
- arXiv:
- arXiv:1106.3572
- Bibcode:
- 2010SoPh..267..107L
- Keywords:
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- Solar flares;
- Magnetic reconnection;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Solar Physics, vol. 267, pp.107-139 (2010)