Panels a)–d): sequence of AIA 131 Å images showing a flux rope proxy tracked by active material of a filament on 2013 December 31. Panels e)–g): corresponding AIA 304 Å and 171 Å images and HMI magnetorgram when the flux rope was well observed. Panels h1), h2): two expanded 131 Å images outlined by rectangles A and B in panel c). The arrows in panel d) mark the parts of the structure that are only visible in the 131 Å band, and the blue and red curves in panels h1) and h2) are contours of the corresponding positive and negative magnetic fields. An animation (movie1.mp4) of the 304 Å and 131 Å channels shown in this figure is available online.