What is the role of the kink instability in eruption of X-ray sigmoids?

Robert J. Leamon, Richard C. Canfield, Zachary Blehm and Alexei A. Pevtsov

Astrophysical Journal Letters, submitted (2002)

Abstract:

Observers see ample evidence of helical structures in erupting solar filaments, X-ray sigmoids and CMEs. It has been argued that the total amount of twist in a given loop is a factor in its MHD stability. A simple cylindrical force-free magnetic field with constant α= T/L, where L is the length of the tube and T is the total twist contained within it, is stable against the MHD kink instability for total twist below a critical value Tc ~ 2π. We determine the total twist of 191 X-ray sigmoids in the Yohkoh SXT data, and identify signatures of eruption, i.e., X-ray cusps and arcades. Independently, we determine the total twist in active regions from vector magnetograms. We find no relationship between the frequency of eruption and total twist. Furthermore, we find that sigmoids, many of which are in the early stages of eruption, have total twist much less than the critical value for the MHD kink instability.