Observational evidence for breakout reconnection

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In solar eruptive events (SEE's, Holman 2012) 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 the flux-rope and overlying fields can occur. Such a breakout reconnection scenario, since Antiochos, DeVore & Klimchuk proposed it in 1999, has been included in many numerical simulations of SEEs, but observational support for it has so far been weak. Nevertheless, this reconnection should be observable, due to associated acceleration of electrons which produce radio emission.   
In solar eruptive events (SEE's, Holman 2012) 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 the flux-rope and overlying fields can occur. Such a breakout reconnection scenario, since Antiochos, DeVore & Klimchuk proposed it in 1999, has been included in many numerical simulations of SEEs, but observational support for it has so far been weak. Nevertheless, this reconnection should be observable, due to associated acceleration of electrons which produce radio emission.   
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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, Holman et al. 2013). Figure 1 shows the dynamic radio spectrum (AIP) and the RHESSI 150-300 keV flux curve. The onset of strong particle acceleration is indicated by a light-brown box in Figure 1, and the radio spectrum is enlarged and contrast-enhanced in Figure 2. It  depicts the dynamic spectrum of a seemingly minute feature (the black arrow points to it) shown spatially resolved in Figure 3. Several radio sources appear instead the previous faint one above the active region: we show the radio images at three frequencies (The Nançay Multifrequency Radioheliograph, NRH, courtesy: The Radioheliograph Group), as well as the RHESSI hard X-ray image.   
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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, Holman et al. 2013). Figure 1 shows the dynamic radio spectrum (AIP) and the RHESSI 150-300 keV flux curve. The onset of strong particle acceleration is indicated by a light-brown box in Figure 1, and the radio spectrum is enlarged and contrast-enhanced in Figure 2. It  depicts the dynamic spectrum of a seemingly minute feature (the black arrow points to it) shown spatially resolved in Figure 3. Several radio sources appear, instead of a previous faint one, above the active region: we show the radio images at three frequencies (from the Nançay Multifrequency Radioheliograph, NRH, courtesy: The Radioheliograph Group), as well as the RHESSI hard X-ray image.   
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Revision as of 20:04, 12 March 2013

Authors: Henry Aurass and Gordon Holman

In solar eruptive events (SEE's, Holman 2012) 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 the flux-rope and overlying fields can occur. Such a breakout reconnection scenario, since Antiochos, DeVore & Klimchuk proposed it in 1999, has been included in many numerical simulations of SEEs, but observational support for it has so far been weak. Nevertheless, this reconnection should be observable, due to associated acceleration of electrons which produce radio emission.

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, Holman et al. 2013). Figure 1 shows the dynamic radio spectrum (AIP) and the RHESSI 150-300 keV flux curve. The onset of strong particle acceleration is indicated by a light-brown box in Figure 1, and the radio spectrum is enlarged and contrast-enhanced in Figure 2. It depicts the dynamic spectrum of a seemingly minute feature (the black arrow points to it) shown spatially resolved in Figure 3. Several radio sources appear, instead of a previous faint one, above the active region: we show the radio images at three frequencies (from the Nançay Multifrequency Radioheliograph, NRH, courtesy: The Radioheliograph Group), as well as the RHESSI hard X-ray image.

The solar eruptive event of November 03, 2003
Figure 1: The dynamic radio spectrum (AIP, top), and the RHESSI 150-300 keV light curve (bottom). The light-brown frame marks the time interval enlarged in Figure 2.
Figure 2: This feature (see the black arrow) is the first impulsive spectral signature of coronal radio emission in this flare, shown spatially resolved above the active region at heights of about 0.18 and 0.41 solar radii in Figure 3. The white lines mark two of the NRH observing frequencies.

The two observed coronal X-ray sources serve to locate the two jets above and below the indicated flare reconnection site. Radially above the active region and the X-ray sources (in projection on the plane of sky) two radio sources are located. The lower one is a counterpart of the upper X-ray source. The upper of these two sources indicates the breakout reconnection together with two other sources seen at lower frequencies (here shown at NRH 236.6 MHz): these flank the upper radially oriented radio sources as nicely seen in Figure 3.

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 source above the flaring active region remained stationary in space in the next minutes of the flare thus indicating the ongoing breakout reconnection process in that height level of the corona.

Figure 3: Evidence for breakout reconnection in the 2003 November 3 SEE from radio- (NRH) and X-ray (RHESSI) data. Contours show radio sources at 432 MHz (red), 327 MHz (cyan), and 236.6 MHz (dark green). The color insert shows the 15 – 20 keV sources (from Veronig et al. 2006). The two 236.6 MHz sources would then naturally be associated with the roughly horizontal jets from the breakout reconnection well above the flaring active region.

The configuration given by Figure 3 marks some progress in our understanding of X-ray and radio data during the very onset of eruptive energy release in SEEs: the excellent timing between the occurrence of the radially elongated radio source formation and the "above the HXR loop top source" (Sui et al. 2004) reveals that both sources belong to the same (the upper flare reconnection) hot and turbulent plasma jet. The observations described here for a near-limb event are reminiscent of the results about another SEE seen in projection on the disc where a radio source in a distance of about 0.3 solar radii from the flaring active region occurred simultaneously with the most energetic X-ray and Gamma-ray emission (see Aurass et al. 2011, 2006).

References:

Antiochos, S. K., DeVore, C. R., Klimchuk, J. A.: 1999, ApJ 510, 485

H. Aurass, G. Holman, S. Braune, G. Mann, P. Zlobec: 2013, A&A submitted

H. Aurass, G. Mann, P. Zlobec, M. Karlicky: 2011, ApJ 730, 57A

H. Aurass, G. Mann, G. Rausche, A. Warmuth: 2006, A&A 457, 681

Holman, G.D.: 2012, Physics Today 04, 56

Sui, L., Holman, G.D., Dennis, B.R.: 2004, ApJ 612, 546

Veronig, A. M., Karlický, M., Vršnak, B., Temmer, M., Magdalenić, J., Dennis, B. R., Otruba, W., Pötzi, W.: 2006, A&A 446, 675

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