Observational evidence for breakout reconnection

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In solar eruptive events (SEE)'s the transition from slow to fast (eruptive) energy release leads to the interaction of a flux rope with the overlying magnetic field. If the flux rope has a field component opposite to that of the overlying field, magnetic reconnection between both fields can become observable due to the associated electron acceleration and radio emission. Such a breakout reconnection scenario is included in many numerical simulations of SEEs, but observational support for it has so far been weak.

[[File:Fig1.png]|left|150px|w:Dynamic radio spectrum (top) and RHESSI flux curve (bottom) [[File:Fig2.png]|right|150px|w:Enlarged dynamic radio spectrum for the time shown in Fig. 3

Strong evidence for breakout reconnection has recently been identified in the combined meter-wave radio and RHESSI X-ray observations of a well-observed SEE (Aurass et al. 2013). Figure 1 shows the dynamic radio spectrum (AIP) and the RHESSI 150-300 keV flux curve. The arrow indicates the onset of the impulsive flare phase. This onset phase of strong particle acceleration in the radio spectrum is enlarged in Figure 2 and depicts the instant shown in Figure 3: the radio images at two frequencies (Nançay Multifrequency Radioheliograph), as well as the hard X-ray images.

The two observed coronal X-ray sources serve to locate the two jets above and below the indicated flare reconnection site. Two radio sources are located radially above the X-ray sources. The upper of these two sources (here at NRH 432 MHz) is flanked by two sources (here shown at NRH 236.6 MHz) along a line perpendicular to the radially elongated X-ray and radio sources.

A plausible explanation for this arrangement is that the lower radio source, like the upper X‑ray source, was associated with the upward-directed flare reconnection jet. The upper radio above the flaring active region remained a stationary source indicating the ongoing breakout reconnection process.

Fig3.png

Figure 3. Evidence for breakout reconnection in the 2003 November 3 SEE from radio and X-ray data. Contours show radio sources at 432 MHz (dot-dash), and 236 MHz (solid black). The color insert shows RHESSI 15 – 20 keV sources. The two 236 MHz sources would then naturally be associated with the roughly horizontal jets from the breakout reconnection well above the flaring active region.

References: H. Aurass, G. Holman, S. Braune, G. Mann, P. Zlobec: 2013, Astron. Astrophys. submitted.

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