XRT Picture of the Week (XPOW)

During the evening of December 17th, 2006 AR10930 produced a small B3.6 flare. Just at the end of this flare, when the solar flux was nearing the background level, a small spike in the x-ray intensity was seen in the GOES solar X-ray flux. That is when XRT observed a beautiful cusp on the western limb. A dark band can be seen between the higher cusp shape and the much smaller inner loops that surround a filament channel. As the movie progresses, the cusp gets dimmer while the dark band appears to grow. It looks as though the loops on the inner part of the cusp are getting pealed off and shrink toward the center of the cusp, kind of like a balloon deflating. The whole while, really bright small loops are popping off at the base of the cusp.

Of course, this can all be explained by magnetic reconnection. It is thought that magnetic reconnection occurs near the top of the cusp, making those loops brighter and the tip of the cusp is formed by outflowing material flowing away from the reconnection site. At the same time, some of the plasma begins to cool and condense, creating the dark band where there is no x-ray emission. This can explain why the cusp gets dimmer and the dark band expands outward. There is also a filament channel at the center of this system and when the cool plasma drains into that magnetic structure, it it again heated and we see the inner loops get bright. The prominence, sitting in a stable flux tube, doesn't react much, it just sits there while its neighborhood gets heated to 10 million degrees.