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arXiv · 1310.1438

Hot Spine Loops and the Nature of a Late-Phase Solar Flare

Xudong Sun·J. Todd Hoeksema·Yang Liu·Guillaume Aulanier·Yingna Su·Iain G. Hannah·Rachel A. Hock
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Abstract

The fan-spine magnetic topology is believed to be responsible for many curious features in solar explosive events. A spine field line links distinct flux domains, but direct observation of such feature has been rare. Here we report a unique event observed by the Solar Dynamic Observatory where a set of hot coronal loops (over 10 MK) connected to a quasi-circular chromospheric ribbon at one end and a remote brightening at the other. Magnetic field extrapolation suggests these loops are partly tracer of the evolving spine field line. Continuous slipping- and null-point-type reconnections were likely at work, energizing the loop plasma and transferring magnetic flux within and across the fan quasi-separatrix layer. We argue that the initial reconnection is of the "breakout" type, which then transitioned to a more violent flare reconnection with an eruption from the fan dome. Significant magnetic field changes are expected and indeed ensued. This event also features an extreme-ultraviolet (EUV) late phase, i.e. a delayed secondary emission peak in warm EUV lines (about 2-7 MK). We show that this peak comes from the cooling of large post-reconnection loops beside and above the compact fan, a direct product of eruption in such topological settings. The long cooling time of the large arcades contributes to the long delay; additional heating may also be required. Our result demonstrates the critical nature of cross-scale magnetic coupling - topological change in a sub-system may lead to explosions on a much larger scale.

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Xudong Sun, J. Todd Hoeksema, Yang Liu, Guillaume Aulanier, Yingna Su, Iain G. Hannah, Rachel A. Hock. 2013-10-05. Hot Spine Loops and the Nature of a Late-Phase Solar Flare. https://doi.org/10.1088/0004-637x%2F778%2F2%2F139

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