Evolution of the GOES soft X-ray flux during 16:00:00 UT to 18:00:00 UT (top panel) and observation of the X1.6 flare in 171 Å (a1–a6), 304 Å (b1–b6), and 1600 Å (c1–c6) bands. The labels T1 to T6 correspond to the time shown in the following panels. The overlaid contours are shown for B_z = 500 G (colored in cyan) and −500 G (pink) in panels a1, b1 and c1. Arrows in panels a1 and b1 indicate the location of the filament. Arrows in panels a2, b2 and c2 point to the circular ribbon of a C7.0 flare. Arrows in panels a3, b3 and c3 indicate the initiation of the X1.6 flare. Arrows in panel b4 show the rising filament with a helical shape. Arrows in panels a5 and b5 point to the eruption of the filament. An animation of this figure is provided online.