Structure and evolution of the MFR and the current density before to after the X1.6 flare. Left column: sampled magnetic field lines shown with different colors for a better view of each field line. Two middle columns: Iso-surface of magnetic twist number T_w = 1 in the x − y plane and in 3D, the structure is false-colored by the value of height z in units of arcsecond (or 720 km). Right column: evolution of the current distribution which is calculated by integration of the current density along the z direction.