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

摘要

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