Reconnection of a kinking flux rope triggering the ejection of a microwave and hard X-ray source. I. Observations and Interpretation

TL;DR

This paper presents observations of a solar flare where a kink instability in a twisted magnetic flux rope leads to reconnection, ejection of sources, and supports the plasmoid interpretation of observed radio and X-ray features.

Contribution

It provides observational evidence linking kink instability to flux rope reconnection and plasmoid formation during a solar flare.

Findings

Evidence of helical kink instability in the flux rope.

Propagation of compact sources at >1000 km/s.

Support for plasmoid interpretation of radio and X-ray sources.

Abstract

Imaging microwave observations of an eruptive, partially occulted solar flare on 18 April 2001 suggest that the global structure of the event can be described by the helical kink instability of a twisted magnetic flux rope. This model is suggested by the inverse gamma shape of the source exhibiting crossing legs of a rising flux loop and by evidence that the legs interact at or near the crossing point. The interaction is reflected by the location of peak brightness near the crossing point and by the formation of superimposed compact nonthermal sources most likely at or near the crossing point. These sources propagate upward along both legs, merge into a single, bright source at the top of the structure, and continue to rise at a velocity $>\!1000$~km\,s$^{-1}$. The compact sources trap accelerated electrons which radiate in the radio and hard X-ray ranges. This suggests that they are plasmoids, although their internal structure is not revealed by the data. They exhibit variations of the radio brightness temperature at a characteristic time scale of $\sim\!40$~s, anti-correlated to their area, which also support their interpretation as plasmoids. Their propagation path differs from the standard scenario of plasmoid formation and propagation in the flare current sheet, suggesting the helical current sheet formed by the instability instead.