Evidence for a pre-eruptive twisted flux rope using the themis vector magnetograph

Although there is evidence that twisted structures form during large-scale eruptive events, it is not yet clear whether these exist in the pre-eruptive phase as twisted flux ropes (TFRs) in equilibrium. This question has become a major issue since several theoretical mechanisms can lead to the formation of TFRs. These models consider either the evolution of a coronal configuration driven by photospheric changes or the emergence of TFR from the convection zone. We consider as a target for addressing this issue the active region NOAA AR 10808 known at the origin of several large-scale eruptive phenomena, and associated with the emergence of a δ-spot. Using the THEMIS vector magnetogram as photospheric boundary conditions for our nonlinear forcefree reconstruction model of the low corona and without any other assumption, we show that the resulting preeruptive configuration exhibits a TFR above the neutral line of the emerging δ-spot. In addition, the free magnetic energy of this configuration could even be large enough to explain such resulting large-scale eruptive events.